Alpha-Hydroxy Acids: The Anti-Aging, Anti-Acne Moisturizing Exfoliators

You’ve seen AHAs in everything. It’s about time we learn how they work.
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Publish date:
November 18, 2013
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anti-aging, exfoliation, acne, alpha-hydroxy acid, glycolic acid, serums, SkinCeuticals, vocab, vocabulary

Previously, we've talked about the grandmama of anti-aging products: a group of pharmaceuticals called retinoids that have been fighting sun damage, wrinkles, acne, and acne pigmentation for decades. Like many people, I love these guys and I credit them with saving me from adolescent acne and preserving my youth.

But as I mentioned then, retinoids are only the first of the Troika of Anti-Agers in the world of cosmetics.

Let's talk about the second member of that triumvirate: alpha-hydroxy acids, a group of ingredients used in cosmetics and professional cosmetic treatments. These acids are in everything nowadays, exfoliating and hydrating the skin of millions of people around the world. It’s about time we learned how they work.

What are Alpha-Hydroxy Acids?

Alpha-hydroxy acids, often abbreviated as AHAs, are a type of acid widely used in cosmetics. The most common cosmetic AHAs are glycolic acid, lactic acid, citric acid, and mandelic acid. They are used primarily as chemical exfoliators and secondarily as humectant moisturizers.

AHAs exfoliate the skin by promoting keratolysis. Keratolysis is the process of breaking down the “brick wall” of dead skin cells, called the stratum corneum, that make up the outer layer of the skin. This means a thinner layer of dead skin cells on the face, which gives a brighter, younger-looking appearance to the skin. The humectant quality comes from the hydroscopic properties of the AHAs, which attract water to the skin.

These qualities--exfoliation and hydration in one ingredient--make AHAs extraordinarily popular in commercial skincare. Since retinoids are available as pharmaceuticals, AHAs have emerged as the keratolysis alternative for over-the-counter cosmetic brands. Most cosmetic skincare products that advertise “skin renewal” or “night repair” are referring to the inclusion of an AHA ingredient.

Concentration, pH, and Bioavailability

The strength of an AHA product is more complex than simply its concentration. An AHA is more effective in an acidic product with a low pH. The higher the pH, the less effective it is. So the FDA rules on how much AHA a product can include involve both pH and concentration.

In order to be considered safe by the FDA, a commercial cosmetic product can use AHAs at concentrations of 10% or less and at a pH of 3.5 or greater. AHA products with concentrations up to 30% and a pH as low as 3 are considered safe if applied by trained professionals in a brief, discontinuous procedure like an in-office “chemical peel” treatment.

But the effectiveness of an AHA is also influenced by its bioavailability, or its ability to penetrate through the stratum corneum and do some biologic action. Basically, the tinier the size of the acid at the molecular level, the easier it can dive into the horny layer to dissolve the bonds between the dead skin cells so that they can fall off down the sink drain.

Why is Glycolic Acid the Most Popular?

The bioavailability of glycolic acid is the reason it is the most popular of the AHAs. It’s teeny-tiny and really good at going deeper than the rest of its siblings. It thus has the most promise for going beyond exfoliation of the stratum corneum for some deep cell action that could make an even bigger difference in the appearance of the skin.

In essence, as time goes by and people do more and more research on glycolic acid, it starts to seem like it acts more like retinoids than originally thought. There is evidence that it, too, can directly stimulate collagen production to keep the skin plump. It also can act like a retinoid in preventing free radicals from messing up the matrix structure of the deeper layers of the skin.

So like retinoids, it keeps the stratum corneum nice and thin, making the skin immediately look fresher and brighter. It can apparently also help reduce wrinkles, acne scarring, and hyperpigmentation. And on top of all that, it’s a moisture-loving humectant that helps moisturize the skin.

This makes cosmetic companies--and their customers--very happy.

Comparison to Retinoids

So this all sounds pretty cool, but despite popular belief, AHAs don’t work in exactly the same way as retinoids. There are some important differences in what they do and who can use them.

First of all, AHAs are classified by the FDA as cosmetics, requiring no prescription. Retinoids are prescription drugs and regulated as such. AHAs are shown to sort of work on acne, in the sense that they keep the pores nice and open, but retinoids have more solid evidence of efficacy against acne right now because they exfoliate and reset the misbehaving cells beneath the surface.

Retinoids are more irritating than AHAs, which makes them bad news for dry skin or rosacea, but AHAs have a nice humectant quality that makes them more appropriate to dry skin types. Retinoids also have way more evidence behind them when it comes to reversing sun damage to the skin.

How to Choose and Use an AHA Product

If you ever need an entertaining read, look up the reprimand letters that the US Food and Drug Administration sends to cosmetics companies that overdo it with their AHA claims. The poor FDA is apparently quite distraught at the downright magical claims some companies use to sell their glycolic acid serums.

And the FDA has a right to be perturbed. Cosmetic companies can go way over the top with promises of age-reversal with these products. Not only that, but they overcharge like crazy. Glycolic acid just really isn’t that expensive and shouldn’t be marketed as an ultra-luxury magical cure. AHAs aren’t going to actually turn a 70-year-old into a 20-year-old, and they aren’t usually as effective as retinoids.

If you are looking to use an AHA product, bear in mind that for the moment, research shows that more intense AHA treatments, such as chemical peels, seem to be more effective than daily use products. If you choose an AHA product intended for daily use, you can apply it in the daytime without fear of the AHA breaking down in sunlight.

AHAs seem to be less irritating than retinoids due to that nifty humectant quality. Yet they do cause some irritation, especially in the stronger formulations. However, a daily AHA serum could be a possible alternative for people who find it too difficult to tolerate the irritation of retinoids.

I am an anti-aging junkie with an aversion to facials, so I work AHAs into my daily skincare regimen. After washing my face and applying my vitamin C serum, I apply a SkinCeuticals Blemish & Age Defense. This serum combines the AHAs glycolic and citric acid for exfoliation, the BHA salicylic acid to kill off active acne, some LHA for exfoliation and as an anti-inflammatory agent, and dionic acid to reduce sebum production. I then finish with a mineral sunscreen before applying my makeup.

A Stern Note on Sun Protection

In a 2003 study, the FDA found that four weeks of an AHA at cosmetic levels lead to 18% more UV sensitivity. The reason for the increased sensitivity is probably the thinning of the stratum corneum from keratolysis.

AHAs aren’t the only things that do this; retinoids also thin out the stratum corneum, and so does mechanical exfoliation with a washcloth or grainy scrub. Because this outer layer of the skin becomes thinner, the deeper layers are closer to the surface and more likely to receive UV penetration.

There’s no point in trying to reduce the signs of aging if you’re just going to expose your skin to UV damage. So if you use anything that thins out your stratum corneum, you've got to sunscreen yourself. Often and copiously. You should be doing this anyway for your health, but vanity is a good motivator as well.

Who else enjoys the look of a thin horny layer? Would any chemists in the audience like to give us their DIY glycolic acid serum recipe?