Hydroxy Acids Part II: The Differences between Glycolic Acid, Salicyclic Acid, Lipohydroxy Acid, and Gluconolactone

Personal/Inspirational, Skin Care

The Dr. Dennis Gross Alpha Beta Face Peel contains Alpha Hydroxy Acids (glycolic acid, malic acid, lactic acid) as well as Beta (salicyclic acid).

About the author:  FutureDerm.com is proud to introduce John Su on our staff as a Contributing Writer.  John is an established skin care expert and aspiring dermatologist.   He also runs a blog, The Triple Helix Liaison, dedicated to providing unbiased, meaningful, and insightful information about skin care. For his full bio, please visit our About page.

Last week, in Hydroxy Acids Part I:  What are Hydroxy Acids?, we differentiated the various types of hydroxy acids (HAs) that one can encounter in the cosmetic and medical industries. I proceeded to enumerate 10+ examples of compounds that fall under the umbrella definition given for HAs. Fortunately for the readers, or those of you who are bored by pages of scientific jargon, only a few of the examples have been widely used to treat skin conditions. The FOUR that will be covered today include the following:

  • (1x) Alpha Hydroxy Acid (AHA): Glycolic Acid (GA).
  • (2x) Salicylic Acid Family (SAF): Salicylic Acid (SA), and Lipohydroxy Acid (LHA).
  • (1x) Polyhydroxy Acid (PHA): Gluconolactone (GUL).

Glycolic Acid

IQ Naturals Glycolic Acid Peel ($24.95) is 30% – very strong for at-home use!

As the most well-known and studied HA, you always hear that GA is great for “exfoliating” the skin. But how does it exfoliate the skin? Several studies suggest that GA exfoliates the skin by manipulating the calcium ion concentrations present in the epidermis (1). Calcium ions play crucial roles in the adhesion of skin cells, specifically in structures like the desmosomes and adheren junctions (2). Now, because AHAs like GA can chelate metal ions (3), its presence once applied topically, will result in an overall loss of the epidermal concentration of calcium ions, which in turn will disrupt the adhesion of skin cells, ultimately leading to “forced” exfoliation.

*Note that because GA is extremely hydrophilic, it will tend to stay away from, and therefore not exfoliate areas that are lipid-rich, like the lining of hair follicles (pores).

What about GA’s alleged claims of helping with anti-aging and hyperpigmentation? Fortunately, GA is a powerhouse when it comes to these issues as well; it addresses them via multiple pathways.

  1. In vitro and ex vivo studies indicate that high-strength GA directly accelerates collagen synthesis in fibroblasts by modulating activation (4).
  2. Furthermore, GA inhibits matrix degradation by stimulating the production of the cytokine, interleukin-1 alpha (IL-1a) (5). Because IL-1a also plays significant roles in other biological interactions including prostaglandin release (compounds related to inflammatory reactions), that may attribute to GA’s irritation potential, overly aggressive and chronic use of GA is not recommended.
  3. GA can also increase epidermal thickness, epidermal and dermal levels of hyaluronic acid (the other HA!), and increased type I collagen gene expression measured by the levels of mRNA (6). The results are positive changes in appearance, texture, and function.
  4. Finally, GA is known to be effective in treating forms of hyperpigmentation such as melasma and solar lentigos. However, in the past it was just assumed that this mechanism of action was due to accelerated remodeling and exfoliation, which will result in faster pigment dispersion. However, some studies have shown that part of GA’s ability to reduce hyperpigmentation is independent from its acidic characteristic. In fact, GA was shown to directly inhibit the tyrosinase enzyme (7). While several compounds such as hydroquinone already operate via this mechanism, why not use GA if it has so many other benefits?

Salicylic Acid

Neutrogena OIl-Free Acne Wash is a reader favorite. Its secret? You guessed it: Salicyclic acid.

Another very well-known HA, SA is known for its ability to treat acne. It does so in a similar fashion as that of GA. However, with the hydroxyl and carboxyl groups attached directly the benzene ring, SA is much more lipophilic than GA. Therefore, it can exfoliate the areas (like in the pores), that GA can’t. However, it does have distinct properties that separate it from GA.

  1. SA is antibacterial, which has the potential to neutralize any P. Acnes that’s present in acne papules and pustules. SA’s antibacterial nature comes from its ability to inhibit the production of various aspects necessary for binary fission (bacterial reproduction), such as fibrinogen, fibronectin, and alpha-hemolysis (8).
  2. SA is also anti-inflammatory, which again is great for treating acne conditions, as any additional inflammation will worsen the breakouts. SA’s anti-inflammatory nature comes from its ability to truncate the arachidonic acid (AA) cascade. This in part, allows SA to suppress the expression of inflammation-inducing genes by the inhibition of transcription activators such as (nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), activation protein-1 (AP-1), and CCAAT/enhancer-binding protein B (C/EBPB) (9), in case you were curious…

Lipohydroxy Acid

La Roche Posay Effaclar Micro-Exfoliant Astringent Lotion is one of the few products on the market in 2012 to contain lipohydroxy acid.

A newcomer and relative to SA, lipohydroxy acid (LHA) is structurally characterized as an SA molecule that has an eight-carbon fatty chain connected to the aromatic benzene ring. This “attachment” allows for LHA to be more lipophilic than SA, while penetrating less deeply, which may partially account for its lower irritation potential (10). Due to this structural modification, LHA appears to modulate trans-membrane glycoproteins and not affect the corneocyte membrane, unlike SA and others (11), which allows LHA to induce desquamation of individual desmosomes, resulting in cleaner and more even exfoliation.

With exfoliation covered, what else can this newcomer do? Besides being anti-bacterial and anti-inflammatory like its parent molecule SA, LHA’s other important characteristic is that it exhibits similar effects as those of tretinoin, albeit less potent ones. LHA has been shown to stimulate renewal of epidermal cells and of the extracellular matrix (12).

While a relatively new compound, LHA is an exciting ingredient that I would personally love to see further researched and elucidated. Its low irritation potential (by being less penetrating and the ability to operate at a pH of 5.5) combined with its (weak) tretinoin-like effects, would be a Godsend for those who have very sensitive skin (like people with rosacea) and cannot use, but still desire the benefits of LHA’s more traditional and irritating counterparts.

*Note that most if not all of the studies cited for LHA are done by L’Oreal Corp, or some affiliated party. L’Oreal owns the sole brand that uses LHA, La Roche-Posay. And while the studies are well-designed and the conclusions are logical, this conflict of interest and source of bias cannot be overlooked. Guess we can only wait until more independent research arises.


Like lipohydroxy acid, gluconolactone can be hard to find in products. Exuviance Evening Restorative Complex contains it.

As stated last week, polyhydroxy acids (PHAs) are AHAs with multiple hydroxyl groups. Even newer than LHA, PHAs represent a new generation (though not necessarily a better one) of HAs because they give similar results as AHAs, without the irritation that usually comes hand-in-hand (13).

Furthermore, PHAs like gluconolactone (GUL) provide additional hydration due to the additional hydroxyl groups, which can attract more water as humectants. GUL has also been shown to work well with other proven ingredients such as tretinoin and hydroquinone (14).

I also find it exciting that gluconolactone has been shown to be just as effective as benzoyl peroxide (BP) at reducing acne lesions (15), without the irritation! That’s great because if you can avoid BP, which operates by generating ROS and ages the skin prematurely, you can deal with acne without hurting your skin. Once again, I’m eager to see more well-designed studies done to examine and analyze the currently unknown mechanism of action and any other potential dermatologic applications.

Phew! While that wasn’t very long, it admittedly was quite technical. Stay tuned for Part 3 (misconceptions of HAs) and Part 4 (product recommendations)! Please let me know your opinions down below in the comments section or better yet, on my blog! And make sure to enter my awesome brush giveaway, which is closing in less than two weeks!


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35 thoughts on “Hydroxy Acids Part II: The Differences between Glycolic Acid, Salicyclic Acid, Lipohydroxy Acid, and Gluconolactone

  1. Patricia says:

    John, thanks very much for answering me on your post “The 5 Most Common Skin Care Mistakes Even Experts Make”. There you mentioned that there are milder versions of retinoids, if it’s possible, I’d appreciate if you could make a post from the mildest to the toughest versions. Fourteen years ago, when I was 17, I took Roacutan for about six months and later I eventually used isotretionin topically (I really liked!). Lately, I’ve noticed tiny spider veins on my chins and I’ve been running away from vitamin A products so far. My skin swings from oily to combination type, I don’t have severe acne anymore, but I’ve experiencing breakouts, and I think that has a lot to do with the fact I stopped taking my birth control pills two years ago (!)and a good dose of stress….
    Do you think that “C E Ferulic” could be a good option as a anti-age and anti-acne treatment?
    Thanks again!

  2. John says:


    You’re welcome. and for future reference I will respond 99% of the time. :) I can quickly tell you, but I’m pretty sure there are articles on FutureDerm that address your retinol question.

    But a quick explanation can be summarized by this pathway:

    Retinyl esters (such as acetate, palmitate) > retinol > retinal (retinaldehyde) > tretinoin. The further away from tretinoin a compound is, the weaker and therefore less irritating it will be.

    Other forms of retinoids (which are not involved in the above pathway) like isotretinoin, adalalene, and tazorac can be less irritating, depending on the user. If I don’t do a post on this topic for FutureDerm, I know for sure that this information will be included as an “Ingredient Profile” on my blog. I already planned everything out, I just have to write them xD.

    I’m sure you don’t have to ask me if the CE Ferulic is “anti-aging”, because Nicki swears by it! She has multiple product reviews and comparisons for this product. I think if you can afford it, go for it! There is excellent documenation behind the product itself, as well as the various ingredients present. It maybe not be great for acne, since the low pH and high % of vitamin C result in quite a lot of potential irriation. I’d say give it a try, just be careful.

    I hope that helped. :)

  3. Rachel says:

    I love these educational articles. I learn so much that guides my next product choices and may illuminate why some products work for me and some do not. However, I’m still wondering why I break out terribly when I use salicylic acid. Since it’s supposed to be anti-bacterial and anti-inflammatory, I am continually tempted to use products with it. But each time, it sends my skin into fits. I end up with multiple spots and even if I stick it out for weeks, it never gets better. Why is this wonderful product impossible for me to use? (I’ve tried Neutrogena, La Roche Posay, etc – all with the same results)

  4. NeenaJ says:

    Thanks for pointing out if the acid “plays nice” with other ingredients. For example, that gluconolactone gets on well with tretinoin and hydroquinone. When I think about adding a new element to my routine, I have to be certain it won’t disrupt the effectiveness of my primary actives (and hopefully enhances it).

  5. John says:


    You’re welcome! I actually didn’t address all the things that can or can’t be used with these ingredients. I planned to do that in Part 4 when I make product recommendations. But yeah, I’m glad you could learn something from all this.

    Thanks for commenting!

  6. BooBooNinja says:

    This is off topic, but your mention of benzoyl peroxide jogged a question. I am allergic to BP — could you recommend an effective alternative? My skin generally stays clear with Paula’s Choice BHA (most mornings and nights) and AHA (some evenings instead of BHAs) chemical exfoliants. However, I my trouble area is around my nose, where I get hormonal (I think) break-outs. The BHA and AHA doesn’t seem to keep these at bay. I’m open to your suggestions!

  7. John says:


    Hey, we’ll I’d like to give you better suggestions by having you submit a routine review request. We’ve discussed this already, so you know that! I’m not sure why else I can tell you, without having more information, since BHAs and AHAs are some of my go-to recommendations. Perhaps a retinoid too, but I can’t know unless you give me more info. :)

  8. John says:


    You may be breaking out because your skin is allergic to SA, which does happen. But it could be a number of things. Stay tuned for Part 4 of this series where I give product recommendations. Perhaps something that I recommend with LHA or gluconolactone is available to you!

    Or if you’d like, I can give you a super detailed review of your entire routine. I’ve done 5 on my blog so far. You can check those completed ones to see if you’d like that. I’ll provide the link for you and anyone else interested about the questionnaire that must first be completed before a routine review can be done.


  9. Alyzze says:

    Where does Mandelic Acid fit in here? I’m hoping to learn more about it, it seems (based on brief readings) to be a great effective and potent choice for those that suffer from PIH .. thoughts?

  10. John says:


    Wow I did not see this comment. I’m not even sure you will see my response lol! But anyways, I’ll answer your question in the hope that you’ll see this.

    Mandelic acid is an alpha hydroxy acid and has some research suggesting that it functions similarly as glycolic acid, with less chances of irritation. However, the sole study (http://www.ncbi.nlm.nih.gov/pubmed/19076192) suggesting this was when MA was used in conjuntion with SA, which of course is anti-inflammatory, so the SA effects could have masked any irritation seen by the MA. Not to mention that 35% of GA was used, versus 10% MA.

    Just to note, it’s pKa suggests that a slightly lower pH (than that required for GA) is required for adequate exfoliation.

    Finally, I’m not really sure what PIH is, except pregnancy-induced hypertension, which is not directly relevant to topical products.

  11. Alyzze says:

    Ok I’m even later than you just revisitng these posts. Thanks for answering.

    I was referring to Post Inflammatory Hyperpigmentation – prevelant in ethnic skin types. I use hydroxy acids/ tretinoin to treat it however depending on the frequency and strength of the treatments and if I have a concurrent breakout, even after I can still develop P.I.H. :-/

  12. John Su says:


    Oh, duh! I completely forgot about that. You need to be careful with PIH since the hyperpigmentation is caused by irritation, rather than say sun exposure. So yes, hydroxy acids and tretinoin can treat hyperpigmentation itself. However, they both tend to be quite irritating, esepcially glycolic acid. However, if you aren’t experiencing any irritationg, than those can still be used.

    Now, because salicylic acid also has anti-inflammatory properties, you may want to use that and other non-irritating skin lighteners. Niacinamide would be very helpful since it is also anti-inflammatory and possesses a host of other beneficial properties including repairing the epidermal barrier. It’s absolutely a multi-purpose superstar. I did a post on niacinamide here: https://www.futurederm.com/2012/09/27/spotlight-on-vitamin-b3-niacinamide-and-nicotinic-acid/


  13. alyzze says:


    Awesome! thanks for the heads up. I was actually considering trying a new product vs cycling Hydroquinone on and off ( my Derm makes a very potent mix w/ 6% for serious scarring which mimics a Tri Luma like combination of a retinoic acid, hydroquinone and L ascorbic acid… but i cant use it for longer than 4 months at a time and even in that frame its too strong for regular maintenance use)

    I know this ingredient has been available in Olay products for some time but had no idea it had barrier repair functionality too, this seems like a great product to use in conjunction wit superficial chemical peels.

    Thanks again!


  14. nelson says:

    hello again! (i thought about this after seeing your review with the perricone md product and thought it would be better if i enquire here!) would the combination of gluconolactone and SA yield better results for acne-prone skin compared to GA and SA? what about your own experience, have you tried using gluconolactone and SA together?

  15. John Su says:


    I have not tried gluconolactone and SA together as my purpose of using the Perricone MD Blue Plasma is not for dealing with acne; rather for gentle and non-irritating exfoliation, and some minor oil-control.

    As gluconolactone is basically a less irritating and less effective version of GA, the former will therefore be less effective than the latter. So I think you will have to try using the different combinations and see which one works bests for you.

    Sorry I coulddn’t be of more help, and I hope that all makes sense.

  16. Kelly says:

    I’m curious as to how you might be able to estimate the salicylic or glycolic % of certain products. I’m looking into switching products and am just wondering. Currently I’m using Olay Skin Smoothing cleaner, which has salicylic acid only to Neutrogena Pore refining cleaner which has both. I’m also hearing alot about Paulas Choice products and thinking about trying those, which seem more science based. any idea the % for those 2 products?? Thanks!!

  17. John Su says:


    Well, I usually state the % of hydroxy acid only if the manufacturer states it on the packaging or on their website, AND if the ingredient placement corroborates and suppots that claim; or, if another reliable source divulges a plausible estimation. But really, there’s no way to pinpoint how much of an ingredient is present in any given fomulation.

    As for the % in the Olay product, I’d guess it’s somewhere between 0.5-1.0%. Similar amounts of GA and SA are likely pesent in the Neutrogena product as well, which are not very high. More importantly however, is that the pH of these scrubs is most likely not sufficently low to allow for exfoliation. Furthermore, since you’re going to be emulsifying them with water, which has a pH of 7, even if the pH were sufficiently low, the introduction of water will raise the pH and reduce or even eliminate efficacy. Finally, the scrub is on your face for likely less than a minute, which is not adequate time for the hydroxy acids to penetate and function, which keep in mind only occurs when all other conditions are met (low pH, adequate concentration).

    All in all, what’s exfoliating you face is the little plastic particles in these scrubs. You’re manually exfoliating the skin, rather than chemically, which is okay. Chemical exfoliation generally provides better results, but it’s up to you on how to exfoliate.

    Does that all make sense?

  18. Simona says:

    Hi John,

    Question for you: there is a claim that Paula’s Choice BHA9 is better than Bravura London’s 10% BHA peeling, because …. Paula’s does not need to be neutralized (?!) and that is specially designed to be a leave in product (?!)

    from my perspective, the only things that differentiates the 2 of them as leave in treatments are:
    1. 9% BHA instead of 10% BHA
    2. BHA9 has some antiiritants and conditioning agents in the formula, when Bravura’s peeling has none.
    3. the price : approx 35 USD paula’s vs approx 12 GBP Bravura’s.
    4. Bravura has discontinued her salicylic acid peelings until they reformulate the products (lucky me- I have a bottle of each !!)

    So, what’s the thing about “neutralizing” salicylic? I have never heard such a thing – the only thing that I know requires neutralization is a glycolic acid peeling. I have used Bravura’s treatments as leave in overnight and noticed the exact same results as when using paula’s BHA 9 treatment. I did apply them after my entire routine finished (so a bunch of antioxydants and antiirritants and skin identical and cell communicating are already on my skin) and I have noticed excellent results, no side efects.

    Also, what makes a BHA product leave in or not? Isn’t this a “marketing” trick to fool customers? I see that they both use PG as primary solvent, so what’s the catch? Paula claims that “The technology behind BHA 9 is indeed unique, allowing for a controlled, sustained release of salicylic acid without diminishing any of its effectiveness.” . OK, so Salicylic Acid (beta hydroxy acid/time-released exfoliant, 9% ?! I have never heard that the plain SA can be “time-released” and to me this sounds really like PURE marketing!

    Below are the INCIs for the 2 products. Personally, I prefer the BHA10 from Bravura, as I live in the EU and I do not have access to paula’s version. As a leave in spot treatment. If I want to use a thin layer on my face once a week after my skin care routine completed, I can always use BHA 5% from Bravura. Below are all ingredients.

    any thoughts? :)

    Paula’s Choice RESIST BHA9: Product Ingredients:

    Propylene Glycol (solvent/penetration enhancer), PEG-75, PEG-8 (thickeners), Water, Salicylic Acid (beta hydroxy acid/time-released exfoliant, 9%), Glycerin (skin-repairing ingredient), Avena Sativa (Oat) Kernel Extract (anti-irritant), Butylene Glycol (slip agent), Boerhavia Diffusa Root Extract (antioxidant plant extract), Sea Whip Extract (soothing plant extract), Arginine (amino acid/skin-conditioning agent), Polysorbate 20 (stabilizer), Disodium EDTA (chelating agent).

    Bravura London 5% BHA peeling (similar to 10% peeling) : Distilled water, Salicylic Acid, Propylene Glycol, Hexylene glycol, Sodium Hydroxide.


  19. John Su says:


    Well, your initial instincts are pretty much correct. Neither product is “better” than the other, because what is “better” for someone may be “better” for another. However, if you define “better” as “the stronger or more potent salicylic acid product” then the 10% Bravura would be the winner.

    In terms of “neutralizing” SA, you are correct that it does NOT need to be neutralized. Even 20-30% SA peels don’t need to be neutralized due to the lipophilic nature and crystallization tendencies of SA. Therefore, all SA skin care products can be considered “leave-on” products,. Although… you may not want to leave SA peels on your face, since there will white crystals scattered all over your face. Lol!

    As for the “time-release” claim, that doesn’t actually refer to the SA molecule itself. An SA molecule is an SA molecule. Instead, it refers to the vehicle and how it releases SA over time. But that doesn’t mean it’s better, more effective, or even a complicated process.

    In terms of the PC product, the “time-release” claim is used just because the SA is suspended in a thicker vehicle, which means that it takes more time for the SA to come into contact with the skin, since the SA molecules have to slowly descend through the more viscous vehicle (via gravity) in order to reach the skin. Notice how PG, and two other PEG-based thickeners are present BEFORE the water content for the PC product? Then look at how water is instead the first ingredient in the Bravura product. It just means that all of the SA content in the Bravura product will reach that skin at approximately the same time. With the PC product, the SA content will slowly be delivered over time.

    Keep in mind that the thickness of the PC product’s vehicle likely prevents complete absorption of the SA content, since some (or many) of the SA molecules are bound to get stuck in the sticky (viscous) vehicle and/or the diffusion rate is very slow. In this scenario therefore, I personally don’t think that the “slow” characteristic is a good thing for a product that’s supposed to be geared towards people who have very problematic skin and need something more potent.

    Does that make sense?

  20. Simona says:

    Hi John :-)

    It makes perfect sense , actually. After writing the comment I thought a bit about the difference in viscosity, but I could not say for sure that this would actually help with the “time delivery”.

    Indeed, the effectiveness of the 10% Bravura London peeling vs the BHA 9 from Paula’s Choice was a bit higher, and your note that not all SA in PC’s product may reach the skin makes sense.

    Anyway, as I am expecting to have some SA soon in my hand, as well as some HEC, I am eager to make my own BHA 9 (or 10?) in a gel, packed with some other goodies to help my acne episodes triggered by god knows what :)

    About the 10% (or 5%) peel over my face and the SA crystals – it makes sense to think that , once the water/ PG are no longer there, the SA can re-crystallize on top of the skin – but due to the lower viscosity, isn’t it more likely that the SA will be delivered where it is supposed to be (in a more aggressive way perhaps?) and that there will be little residue likely to crystallize on the skin? I have not noticed any fine white powder in the morning or one hour after applying the peeling on the problematic skin areas, but then I would not expect to see such a thing with my eyes, maybe under the microscope :). But what would be the danger in this?

    Anyways, thanks for the most wonderful articles that you are writing, and for taking your time to get back to each of the comments, science is cool even when not in my area of expertise :)))))


  21. John Su says:


    Glad to hear it makes sense!

    I apologize for the lack of clarity. What I meant by the crystals forming–I was only referring to the high strength (20-30%) peels that I mentioned in my original response to you, not the specific (and relatively weaker) peels that you are using. :) And there’s no danger from this at all. It’s just a cosmetic issue.

    Also, you are correct that due to the lower viscosity, the SA in the Bravura product is being delivered to your skin rather quickly and pretty much all at once.

  22. Sinead says:

    I’m so happy you are doing this series!! My Paula’s Choice 1% BHA is one of my favourite products in my routine and has made such a difference to my skin.

    My question is this: I have heard and read on other blogs that Hydroxy Acids “thin” the skin and therefore shouldn’t be used too much. And that they shouldn’t be used around the eye area which already has very thin skin. This freaks me out as I already have thin skin! I read conflicting things…. Is it true that this “thinning” is actually the layers becoming more dense and therefore healthier? You mention that GA increases thickness and stimulates collagen synthesis. Is this true for SA or only for GA?

    Thanks again for your well written and informative article!

  23. John Su says:


    You’re welcome, and thanks for reading!

    Well HAs do thin the skin. But specifically the stratum corneum (SC), which is the very top layer of “dead” cells. But that may be a good thing since a thick SC manifests as dull skin. By thinning it, you’ll have that “glow” that many people seek. It can also take care of some forms of flaky skin, depending on the cause of course. Just make sure to moisturize afterwards because the SC is what’s responsible for retaining your skin’s moisture (water) levels. But don’t worry, HA products don’t thin the living parts of the skin: epidermis and dermis.

    And it’s true that the general rule is that you want to avoid the eye area, because the skin is delicate there. However, that doesn’t mean you CAN’T use HA products around the eyes. Just use an appropriately low strength one if you have say, milia. But it’s really up to you. For example, I used the PC 2% SA Liquid to rid mine years ago, and the skin around my eye area is perfectly fine. :)

    As for making the layers of skin more dense, that may be true depending on the original condition of your skin. But retinoids are more known to do that than HAs.

    Finally, as for GA increasing the thickness (of the epidermis and the dermis), that is more relevant when it comes to high-strength GA peels and treatments where the concentration is at least around 15-20% at an appropriately low pH. While some may occur at lower strengths (say 5-10%), the GA is mostly just exfoliating and acting as a humectant for the stratum corneum and the upper epidermis in this situations. There’s not much (if any) collagen synthesis occurring. And yes, this only applies to GA not SA. SA does not penetrate past the SC, so no collagen stimulation is possible.

    Does that all make sense?

  24. Sinead says:


    Yes, that all makes sense. Thank you SO MUCH for your detailed reply! I have been trying to get to the bottom of those issues for ages, and I really appreciate you explaining it all.

    The claim on my PC 1% BHA lotion is that it “increases collagen production”. But, since SA doesn’t penetrate that deep, I guess that is not true.

    Thank you again for your great post and replies!

  25. Mary says:

    Hi John — do you think skin can develop a tolerance/resistance to ahas and retin-a when used for years. I’ve used retin-a for 20years and my skin is the better for it for sure. But now even at 1%, retinol doesn’t do much for me and neither does a strong glycolic like MD Forte 20% (I think — it’s one of the strongest anyway.)
    But also: I had a bad experience with IPL and I wonder if you could comment because I’ve heard that after IPL the skin doesn’t benefit anymore from retinoids. My experience is that my face was very hot afterwards and for much of the time even weeks afterward. One mos after I had grooves under my eyes and now my pores are orange-peely– just completely different from the way it was before. I do think glycolic has helped a bit and I found a great (expensive La Prairie) eye gel that helps a lot. Can you tell me anything about IPL and if you think it makes sense to heat up the underlayers of skin in order to cause the collagen to Re-Grow??I feel like the opposite happened. It lightens spots yes but it also seemed to dull my skin color- sort of sucked life out of it. I know this is depressing. Just wonder if you have any thoughts– thank you

  26. John Su says:


    You’re welcome! I’m so glad to lay those issues to rest for you.

    As for the collagen product claim… well, it’s really overreaching.

    The claim stems from the idea that the anti-inflammatory characteristic of salicylic acid (SA) (again at very high concentrations) is able to affect the prostaglandin pathway by inhibiting various cyclooxygenase (COX) enzymes. These COX enzymes play a part in activating the synthesis of several inflammatory cytokines like interleukin-1 alpha, which can inhibit collagen production. Therefore, salicylic acid can inhibit the inhibition of collagen production… thereby, increasing collagen production. Talk about a double negative!

    But as you can see, SA doesn’t actually stimulate collagen production. It just may inhibit or reduce the inhibition of collagen production induced by inflammatory cytokines–a scenario that you will encounter from excess sun exposure and other sources of inflammation like cuts and bruises.

    But if you take care of your skin already, you definitely will NOT see any collagen production with SA, especially not at 1.0%! Like I said, the claim is HIGHLY overreaching.

    I think it’s best to not really pay much attention to claims anymore on skin care products, regardless of who is saying them. I know I don’t. :)

  27. Sinead says:


    Great information! Now I see how those claims are made and how overreaching they are. As I mentioned, I’ve been trying to research this topic for a long time and haven’t had any substantial information until now!

    Yes, I totally agree with you about not believing skin care claims. That’s why I’m really trying to educate myself so I can make wise decisions. And your articles are a big part of that, so again – thank you!!!


  28. John Su says:


    Hm, there’s a distinction between your skin getting used to a product to the point where it is no longer effective (which rarely every happens), versus your skin building tolerance to a product’s initial irritation potential (which happens quite often).

    But in your case, it’s likely that after 20 years, your skin is simply no longer as easily affected by skin care ingredients as it was before. This could be due to a variety of reasons such as sun exposure, lifestyle, etc… You have to ask yourself: Do I wear sunscreen religiously and do I apply enough? Which sunscreens have I used? Are they any good? Do I smoke, etc…?

    Another issue could be that the products that you’re referring to may appear to be very potent based on the concentration of a specific ingredient (i.e. retinol or glycolic acid), but in fact are not. Case in point: all MD Forte poducts, while boasting very high %s of glycolic acid, have relatively high pH ranges (somewhere around your skin’s pH of about 5.0). This means that very little free acid is present in solution, which means that most of their products actually aren’t very potent (Free acids are what’s responsible for any exfoliation). As for the 1% retinol product, the product may not be very effective, depending on the formulation itself. You may want to consider switching to prescription retinoids if you think retinol is not effective enough for you, just to eliminate the conversion process.

    And you have to remember that even the best skin care ingredients can only do so much. We’re all going to age, so you can’t expect the same products to work equally well after 20 years. I’m not saying your skin is bad; I’m just trying to point out some issues that may be relevant in your situation.

    As for IPL making your skin nonresponsive to retinoids, that’s completely untrue. Studies have shown that retinoids greatly enhance the effects of IPL treatments. :) As for the effects of the IPL, well to be honest, I’m not quite as versed in the various laser treatments as I am with topical skin care. However, from what I know, IPLs tend to not be very effective because they don’t provoke a massive healing response, due to reduced damage. So in your case, that’s a good and bad thing. It’s good that the worst case scenario shouldn’t be too bad. But it’s bad that the best case scenario isn’t very good either. But I saw your other comment and I think you may want to check if you actually got an IPL treatment, because Syneron is a company, not a specific type of laser treatment. Fraxel on the other hand, is a specific type of laser treatment.

    I mean, if the person who operated on you didn’t know this… well, I don’t want to make you nervous but perhaps he/she didn’t really know what he/she was doing. I’d recommend getting a consultation with a qualified board-certified dermatologist in your area.

    Okay phew, that was a lot of information jumbled together. Does that all make sense to you? Feel free to ask me follow up questions if anything is unclear.

  29. Pingback: Alternatives to AHA: Discussing Other Chemical Exfoliation Methods | thehoneyseed

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