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Like having the appetizer and the dessert, or maxxing out your credit card with the Chanel and the Fendi, sometimes you really can have too much of a good thing. And while you may not think it, there are some combinations of beneficial skin care ingredients that lose effectiveness when they are used in conjunction together. Here are some of the surprising combinations of ingredients you may wish to avoid:
1. Niacinamide and Sirtuins
In this 2005 study conducted at Johns Hopkins University, it was found that free nicotinamide (i.e., niacinamide) inhibits sirtuin activity in a mechanism mediated by niacinamide binding in a conserved pocket that participates in NAD(+) binding and catalysis. In plain English, this means that your attempts to prolong the life of your collagen-producing fibroblasts by turning off unnecessary gene expression with sirtuins will most likely be negated by niacinamide. Which makes sense, really: when your body wants to turn off the action of sirtuins, it naturally produces additional quantities of related compound nicotinamide adenine dinucleotide (NAD).
So what are you to do if you want both the skin-friendly benefits of niacinamide (reduction in hyperpigmentation, red spots, sallowness, and the appearance of fine lines and wrinkles) and sirtuins (proposed prolonged collagen production)? Two options come to mind: One, use the ingredients in alternating skin care regimens. By using sirtuins without niacinamide periodically for weeks at a time, the theorized turnoff of fibroblast gene expression could take place. However, it is unknown what would occur when you stop using products containing sirtuins and the fibroblasts are turned back on. It is possible that it is more stressful to turn fibroblast gene expression on and off, but then again, it is also possible that fibroblast life is like a bank: take a little out here, stop for a while without penalty, take a little more out until there is no life left. At this point, it is hard to say, and I cannot find research to support either theory. (Please let me know if you are aware of such information!)
The other option is to use products with niacinamide and preserving your skin’s collagen production levels with other proven methods, which include UV ray avoidance, use of retinoids and antioxidants, and stimulation via certain dermatological treatments (CO2 laser, microdermabrasion, and even Botox, according to some reports). As always, talk to your dermatologist to customize your optimal skin care regimen.
2. Retinoids and AHAs/BHAs
According to Dr. Leslie Baumann, M.D., Chief of the Department of Cosmetic Dermatology and Professor of Dermatology at the University of Miami, retinoids should not be mixed with BHA (salicylic acid) or AHA (glycolic acid) because the BHA and AHAs can inactivate the retinoid. Instead, Dr. Baumann recommends using BHAs in the morning under sunscreen and retinoids or AHAs at night, as BHAs may thin the skin and sensitize the sun, but this has not yet been proven, whereas retinoids and AHAs have been proven to sensitize the skin to the sun.
So why should retinoids and AHAs and BHAs not be used together? One answer is that the optimal pH environment for each ingredient differs. For instance, in Dr. Baumann’s Cosmetic Dermatology textbook, it is noted that the optimal pKa of AHAs is approximately 3.83, whereas for BHAs it is 2.97. (When the pH is greater than the pKa, the inactive “salt” form of these acidic ingredients predominates). Given that the the pH optimal for retinol esterification (which may be thought of simply as activation) is reported in the Journal of Investigative Dermatology to be between 5.5-6.0, it would be virtually impossible to achieve a pH in which the activity of all three ingredients would be optimized (i.e., pH < pKa for AHAs/BHAs) and in which all the ingredients are included in effective concentrations within the same solution, or when applied to the skin synchronously.
Another reason why you may not wish to use AHAs, BHAs, and retinoids together is because all may work, at least in part, by thinning the stratum corneum (the outermost layer of skin). While it has been proven in Dermatologic Surgery (amongst others) that the overall thickness of the skin is increased with AHA use, it has also been established that both AHAs and retinoids thin the stratum corneum. Furthermore, while it has been well-documented that retinoids increase photosensitivity, some studies show that AHAs increase photosensitivity and other studies show that AHAs actually have a photoprotective effect (according to the textbook Cosmetic Dermatology by Dr. Murad Alam et. al.). With that said, until the verdict is officially out, I think I personally will avoid using AHAs and retinoids together, and I will certainly restrict retinoid use to nighttime. As for what is best for you – I’ve said it once, I’ll say it again – always talk to your dermatologist.
3. Vitamin A and Vitamin C (mostly as L-Ascorbic acid)
Now, before I start this, I just want to affirm that there are many, many great formulations with vitamin A (i.e., retinoids, retinol, retinyl palmitate, etc.) and C that are out there. However, to achieve the full-fledged benefits of each ingredient, you may just want to apply them separately (i.e., products containing vitamin C in the morning, products containing vitamin A in the evening). The reason? Again, a matter of optimal pH: it has been reported in the Journal of Dermatological Surgery that vitamin C and its derivatives should be formulated at a pH under 3.5 in order to allow the vitamin C to enter the skin (at this pH level, the molecule is protonated and thus can penetrate the skin). Unfortunately, the pH optimal for retinol esterification, as mentioned before from the Journal of Investigative Dermatology, is between 5.5-6.0. This doesn’t mean that products containing vitamin A and C don’t work – many products I love contain both! – but it does indicate that using them separately may be a bit more beneficial. (For even more benefit, I like using vitamin C, which is a proven network antioxidant, instead in conjunction with other network antioxidants [vitamin E, coenzyme Q10, glutathione, lipoic acid] for increased antioxidant power).
One further note: the form of vitamin A and vitamin C does matter when it comes to pH considerations. Although vitamin C as L-ascorbic acid has the highest natural antioxidant concentration in the skin and the most researched benefits to date, other less acidic (higher pH) forms do exist. According to a 1997 study in the Journal of Pharmaceutical and Biomedical Analysis, magnesium ascorbyl palmitate has greater stability than both L-ascorbic acid and ascorbyl palmitate. Magnesium ascorbyl palmitate also has an optimal pH of 7.0-8.5. Therefore, it is definitely possible to make a formulation with a beneficial pH environment using vitamin A (optimal pH 5.5-6.0) and quite a small amount of vitamin C derivatives like magnesium ascorbyl palmitate. However, given that it is unclear what effect combining L-ascorbic acid with moisturizing vehicles may have on its action and what concentrations of many vitamin C derivatives are required for full benefits, I may stick to my separate use of vitamin A and vitamin C, at least for the most part.
While using niacinamide + sirtuins, vitamin A + AHAs, or vitamin A + vitamin C together is very unlikely to be harmful, it seems that using certain ingredients separately may get you the most benefit, or the biggest bang for your buck, if you will. With that said, I personally love vitamin C and other antioxidants, niacinamide or nicotinic acid, and sunscreen galore in the morning, while I save retinoids and peptides and non-vitamin C antioxidants for night. As always, you can find a dermatologist to help optimize skin care for you through the American Academy of Dermatology website here.