Tomatoes, Lemon, Olive Oil, and More: Are They Food, Skin Care Ingredients, or Both?

Nutrition, Skin Care
Ingredients that are good for eating and skin

Is healthy food skin care? In a word, no. Not always.

However, thanks largely to the organic and natural product movement, there are a lot of well-intentioned people out there who say things like:

Let thy food be thy skin care.

If my eighth-grader can’t pronounce it, I won’t eat it or use it on my face.

If I can’t eat it, I won’t use it on my face.

Unfortunately, there are anatomical and physiological differences between the skin and the digestive tract that make them react differently with varied types of ingredients, both synthetic and natural. These differences include:


Though it is somewhat debatable, there is a generalized belief in the nutrition world that an alkaline/basic, or high-pH, diet is best for your health. This is because the hydrochloric acid in your stomach has a pH of approximately 2, neutralizing and ultimately breaking down high pH food residues much better than acidic food residues. It doesn’t hurt that the vast majority of healthy fruits and vegetables are either alkaline (like leafy greens) or leave an alkaline ash in your system (like lemon and other citrus fruits).

On the other hand, the exact opposite is true with your skin: Acidic or neutral pH products are best for your skin. This is because your skin has a natural barrier that is significantly disrupted by agents with a pH higher than 7.0 (Skin Pharmacology and Physiology, 2006). Your skin becomes more exfoliated with products that are highly acidic, with a pH of less than 5.5. (Hence why glycolic acid peels are so popular!) And your skin’s healthy physiology, containing microflora and healthy bacteria, is maintained at a neutral pH (Acta Dermato-venereologica, 1990).



Stomach vs Skin Absorption

The skin evolved to protect your internal organs from potential harm. On the other hand, the digestive tract evolved to absorb as many key nutrients as possible.

Obviously, there are key differences in absorption and penetration here. For instance, the 500 Dalton rule dictates that any ingredient greater than 500 Daltons in size cannot penetrate the skin (read more), but trace amounts of molecules much smaller than 500 Daltons are regularly absorbed — and have systemic effects — when ingested. But smaller amounts of substances like arsenic can be very harmful when ingested.

This is one reason why I am so opposed to studies that show an ingredient is harmful when ingested, and then other well-meaning persons without a scientific background spread the rumor that this ingredient must be harmful to the skin. They’re completely different organs, with different functions and absorption rates.

Enzymatic Breakdown

Part of the reason why the skin and digestive tract act differently towards different ingredients has to do with the degree of enzymatic breakdown in the digestive tract.

Let’s look at this with an example. Take oatmeal, for instance. When ingested, oatmeal is an excellent source of fiber, manganese, molybdenum, and phosphorus, amongst other nutrients (source). But when topically applied to the skin, it is not the fiber or the trace minerals that benefit your skin. In fact, the thick nature of the oatmeal doesn’t allow significant breakdown so your skin can even access many of the trace minerals, much less absorb them. Instead, on the skin, oatmeal helps out the skin with including 60-64% polysaccharides, lipids, enzymes, saponins, prostaglandin synthetic inhibitors, vitamins, and flavonoids (Cosmetic Dermatology, 2008). It’s been shown to penetrate the skin deeply enough to help reduce wrinkles and fine lines over time (International Journal of Cosmetic Science) — but it’s not the fiber, manganese, molybdenum, and phosphorus that are so beneficial for your digestive tract!

Here are some examples of how pH, absorption, and enzymes can make a huge difference between how a food reacts with your digestive tract and with your skin:

Foods that are Great to Eat, but Bad to Apply to the Skin

Foods that are great to eat but bad to apply


  • Tomatoes – increase sun sensitivity
  • Lemon – increase sun sensitivity
  • Milk – may enhance breakouts if not hormone-free
  • Algae extract – highly irritating
  • Turmeric – turns skin orange unless tetrahydrocurcumin is extracted
  • Earl of bergamot tea — can cause severe irritation

Tomatoes are great sources of vitamin C and lycopene when ingested. Yet extra lycopene or beta-carotene could subject your skin to harm.  Matrix metalloproteinases are enzymes that degrade collagen.  At least one study shows applying lycopene or beta-carotene increases matrix metalloproteinase formation 1.5 to 2 times after UVA light exposure! (Free Radical Biology and Medicine, 2002).

Lemon is also a great source of vitamin C, and it forms an alkaline ash when ingested (American Journal of Clinical Nutrition, 1968). But when used on the skin, lemon is associated with increasing the skin’s susceptibility to sun damage to the extent that too much lemon can cause blistering (Photoimmunology, Photodermatology, and Photomedicine, 2005). I have also been sent emails from readers who have used lemon on their skin and had really bad reactions to it. I recommend using lemon only with a broad-spectrum UVA/UVB sunscreen, or better yet, not at all.

Milk is one of those ingredients that even some dermatologists recommend to patients; I’ve even read a few well-esteemed dermatologists advise to put milk on a cotton ball and swipe it all over your face. But this is a bad, bad idea with most forms of milk, which may enhance DHT (androgen) production in the skin, leading to breakouts (Journal of the American Academy of Dermatology, 2008), whether topically applied or ingested.

Algae extract is applauded by two of my favorite nutritionists and authors, Candice Kumai (food editor at SHAPE) and Kimberly Snyder (author of The Beauty Detox Diet). And why not? When ingested, algae extract is replete with tons of nutrients, including phytonutrients, iron, manganese, copper, zinc, and omega-3 fatty acids ( But when topically applied, algae and seaweed of all kinds can be a nightmare for the skin if they are not properly purified, associated with irritation and atopic dermatitis (British Journal of Dermatology, 2006). Some skin care companies still claim that seaweed may have anti-tumor and anti-carcinogenic effects when used topically, but these studies typically feature only a beneficial portion of the seaweed plant, and they are always, always purified (Experimental Dermatology, 2009).

Turmeric has been proven to have potent anti-carcinogenic activity when it is used as a food additive. But when applied to the skin, turmeric is still a double-edged sword. On the one hand, turmeric has potent antioxidant activity, as has been shown in the Journal of Ethnopharmacology, amongst numerous other sources.  It has also been suggested by Dr. Nicholas Perricone, M.D., amongst others, that turmeric may boost the skin’s sun protection when applied under sunscreen, but this suggestion has not (to the best of my knowledge) yet been substantiated in any published, peer-reviewed research as of yet. What is known about using turmeric topically is that it will dye the skin orange, unless a compound known as tetrahydrocurcumin is removed from it (read more), but tetrahydrocurcumin is potent (Molecular Nutrition and Food Research, 2011). For now, I avoid it.

Earl of bergamot tea also has significant anticarcinogenic properties (Archives of Dermatology), but it also contains limonene, which has been shown in patch tests to cause irritation that can last for up to 24 hours (Journal of Agricultural and Food ChemistryInternational Programme on Chemical Safety). Plus, limonene will increase your skin’s sensitivity to the sun, which is less-than-ideal for your already sun-damaged skin (JAADContact Dermatitis).

Let’s look at the case of a 33-year-old woman admitted to a hospital burn unit in the United Kingdom with 70% superficial partial thickness burns. After using six drops of bergamot oil and six drops of geranium oil in an aromatherapeutic bath, she then went into a tanning bed, after which she saw increased redness and blistering for 48 hours. Doctors determined that the sole cause was a compound called 5-methoxypsoralen, which is found bergamot oil (British Journal of Dermatology). Terrible. Again, food is not always skin care, and vice versa.

Foods that are Great to Eat and Great to Apply to the Skin

Ingredients that are good for eating and skin

Vitamins A, B3, B5, C, D, E, and K are all necessary nutrients to ingest, and are beneficial to the skin.

  • To summarize the skin benefits, vitamin A compounds are retinoids, that are wrinkle-fighting, skin-firming, and exfoliating (read more).
  • Vitamin B3 is niacinamide, which is hydrating and helps with skin sallowing (read more), whereas vitamin B5 is the hydrating and wound-healing pantothenic acid (European Surgical Research, 1995).
  • Vitamin C is available in multiple forms, including L-ascorbic acid, tetrahexyldecyl ascorbate, ascorbyl palmitate, and sodium ascorbyl phosphate. While more acidic forms are more exfoliating and newer forms are more stable, the same truth remains for all: they have been shown to increase skin firmness, fight sunspots, and grant skin a “glow.” (read more)
  • Vitamin D has more limited benefits in the skin, but has been associated with antimicrobial activity in the skin (Science, 2006).
  • Vitamin E strengthens the action of vitamin C and is quite hydrating (read more).
  • And lastly, vitamin K has been shown to fight dark circles around the eyes when used in conjunction with a retinoid and vitamin C (Journal of Cosmetic Dermatology, 2004).

Most monounsaturated cooking oils like coconut oil, olive oil, and avocado oil are great for use for the skin, so long as you are careful with what you use in conjunction with them, as these thick oils can trap moisture (and other ingredients!) into your skin.

  • Coconut oil has been shown to have hydrating potential more significant than mineral oil (Dermatitis, 2004). Even though a lot of the other claims I hear in natural and organic product circles regarding the skin-friendly benefits of coconut oil when topically applied to the skin are largely unfounded, it is still unlikely to do any harm when applied topically with the right ingredients.
  • Olive oil has substantial anti-carcinogenic, antioxidant, and hydrating effects (read more).
  • Avocado oil can be skin-softening, antioxidant, and have potent hydrating effects (read more).

Green, white, and red teas are shown to fight skin cancer when ingested (yes, you read that right) and to have anti-wrinkle, antioxidant, and soothing properties when applied topically (read more about green tea).

Cucumbers have been used in ethnic medicine when ingested as a diuretic, treatment for hypertension, and to reduce swelling and inflammation (Mosby’s Handbook of Herbs and Natural Supplements). Their water content, low calories, and decent level of fiber are greatly touted, but they contain relatively few vitamins and nutrients compared with other veggies on their own (Cambridge World History of Food). By concentrating them, products can make the most of their vitamin C content, which works as an antioxidant, increases collagen, and reduce wrinkle formation. In one study, a concentrate was shown to be good for skin brightening and anti-acne purposes (African Journal of Biotechnology, 2011). Future studies will need to determine how well cucumber extract works for fighting wrinkles, dry skin, and psoriasis. However, without concentrating cucumbers in pre-made products, I’m afraid individual cucumber slices used at home aren’t going to do all that much.

Oatmeal extract has been shown in studies to relieve pain and itching by inhibiting prostaglandin synthesis. Also, studies published in the Journal of Drugs in Dermatology  suggest using colloidal oatmeal as a first-line treatment to alleviate the symptoms of psoriasis, eczema, and atopic dermatitis.  It is suggested that use of colloidal oatmeal to treat these conditions may allow for reduced need of topical drugs like corticosteroids or calcineurin inhibitors, which have more known potential side effects than colloidal oatmeal.

Grape seed extract is another ingredient that is great for you inside and out. Grape seed extract is excellent antioxidant because it contains procyanidins, which inhibit lipid peroxidation, the process in which pesky free radicals steal neighboring electrons from lipids in cell membranes to cause cell damage, a sign of microscopic aging (Phytotherapy Research). Topical application of grape seed oil has also been found to provide protection against UVB radiation, promote wound healing, reduce vascular engorgement, and even inhibit Streptococcus bacteria.

Foods that are Bad to Eat, but Great to Apply to the Skin

  • Sugar (when used as a scrub on the skin)
  • Caffeine

Sugar is like death to your insides when you overeat it; excess sugars tend to induce glycation, which can cause hardening of the arteries, clogging of the kidneys, and, yes, aging of the skin. But when you apply it to your skin as a scrub, sugar is genius. It has a round, small shape that exfoliates the skin well. Mix it with a little olive oil and rinse thoroughly for smooth, smooth skin.

Caffeine is a drug. An approved-by-the-FDA-in-reasonable-amounts drug, but a drug nonetheless, and one that can cause chest pain, arrhythmias, trouble breathing, hallucinations, and convulsions (amongst other symptoms) when overdosed (Healthline, 2014). On the other hand, topical application of caffeine or caffeine sodium benzoate have been shown by Lu et. al earlier this year to have a sunscreen effect, enhance UVB-induced apoptosis, and inhibit UVB-induced skin carcinogenesis when applied to the skin of mice. The exact mechanism by which caffeine achieves these aims is not yet known, but it may be related to the fact that the caffeic acid found in caffeine has been found to have some antioxidant activity. Topical application of caffeine additionally dehydrates skin cells, making the skin temporarily appear smoother. a diuretic (making the skin temporarily appear smoother).

Lastly, caffeine is a vasoconstrictor, and its topical application may reduce the appearance of under-eye puffiness and dark circles, although only those caused by vasodilation. Dark circles may also be caused by excess production of melanin, in which cause caffeine would not most likely help.

So while I wouldn’t recommend too much caffeine or sugar for your diet, prudent use of it in your skin care can be a beautiful thing.

Foods that are Bad to Eat and Bad to Apply to the Skin

  • Dairy products

Dairy and Sugar and Acne

If you are looking for specific studies, you’ve also come to the right place.  When it comes to linking milk consumption and acne, there is arguably no better source than F. William Danby at the Harvard School of Public Health. Danby and his team studied more than 47,000 women, asked to complete questionnaires relating to their diet as teenagers and to say whether they had ever been diagnosed with severe acne. The study found no link between food such as chocolate and chips and acne, but found one between women who had acne and those who had drunk a lot of milk.  Danby proposes this is due to the DHT (androgens) in the milk, which increase oil production (Journal of the American Academy of Dermatology, 2008).

Bottom Line

Food is not skin care, as beautiful as that concept would be. The skin and the digestive tract have vast differences in pH, absorption/solubility, and enzymatic breakdown/lack thereof that make different ingredients have varied — and sometimes drastically different — effects on the skin and inside the body.

Use our handy guide here, and be careful when natural or organic companies are trying to sell you “food” as skin care. Similarly, be cautious of anyone who tells you all natural or organic ingredients are hokey as well. Science doesn’t discriminate — there is good in natural and good in synthetic, you just have to do the research and study it well to determine what is truly good for you and what is not.

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