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The Truth About Acids

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July 25, 2016 Reviewed by Marta 4 Comments

Dropping acid recently came up in a team discussion at the Truth In Aging office — I’m a girl of the seventies after all. Seriously though, we were discussing the cosmetic kind and it dawned on me that there are many active acids that bear the name yet have very different effects on the skin.

When I talk about acids, I’m typically referring to alpha hydroxy acids and beta hydroxyl acids, both of which are plant-derived ingredients that exfoliate in various ways. Other common ones, such as ferulic or hyaluronic acid, don’t belong in these groups nor in the exfoliating category at all — although they do other important things for our skin.

As a consumer, it can be very confusing. How do you know what’s best for you? Let’s take an acid trip and sort them all out.


Alpha hydroxy acids

Alpha hydroxy acids (AHA) are clinically proven to loosen the glue-like substances that hold skin cells together, thus shedding the top layer of dull and damaged skin. The AHA family includes glycolic acid from sugar cane, lactic acid from sour milk, citric acid from citrus fruits, malic acid from apples, mandelic acid from bitter almonds, and tartaric acid from grapes and tamarinds.

Glycolic is probably the most commonly used in skin care, as it’s the AHA with the smallest molecule and the greatest penetration. Glycolic acid deeply exfoliates to remove skin that is dry, coarse or dead. Mandelic acid’s relatively large molecular size makes it one of the least irritating AHAs; it still does a good job of exfoliating and is said to help prevent dark spots.

Beta hydroxy acids

Unlike alpha hydroxy acids, which are water-soluble, beta hydroxy acids (BHA) and BHA-esters are lipid (or oil) soluble. This means that they not only exfoliate the upper layer of skin, but also penetrate deep through the epidermis to rid the dead skin cells and excess oil built up in the pores.

The key BHAs are salicylic acid, willow bark (a natural source of SA) and caproyl salicylic acid, the ester that is sometimes referred to as LHA. While many other exfoliants (i.e. AHAs) often irritate the skin, salicylic acid does the opposite by reducing inflammation. This is due to the fact that it shares a similar chemical composition as aspirin, a well-known analgesic and anti-inflammatory. Salicylic acid usually works best at a concentration of 1-2 percent and pH level of 3 to 4.

What they are good for

When our skin cells turnover, they migrate to the skin surface where they die. However, a dead cell is like a poltergeist that can hang around causing trouble and that’s why exfoliation is so important.

Alpha hydroxyl acids exfoliate the surface of the skin, accelerate cell turnover and some, such as lactic acid, act as humectants. They tend to be best for dull, dry or sun-damaged skin. Beta hydroxyl acids go deeper and actually rid the dead cells that hang around in the skin’s pores, leading to inflammation and breakouts. BHAs are choice for oily or acne-prone skin types.

Potential side effects

Caution when dropping acid: Both groups of hydroxy acids increase the skin’s sensitivity to the sun. I have read that beta hydroxy acids can do so by 50 percent. Therefore, it is prudent to use these products at night or follow up with a broad-spectrum sunscreen with SPF 30 or higher.

Irritation is very much a personal thing. I used to be very nervous around this family of ingredients, but have since discovered that a balanced mix of acids is well tolerated, whereas a hefty dose of glycolic acid will be too much for my skin.

Reproductive and developmental toxicity have been associated with exposures to salicylic acid and beta hydroxyl acids, so they are typically contraindicated for pregnant women.

The faux acids

Confusingly, you’ll see other acids in your skin care products. For example, Dr. Dennis Gross, who is well-known for his hydroxy acid peels, frequently makes ferulic acid a star ingredient in his anti-agers. When you see this you could be forgiven for thinking that ferulic is an exfoliating acid similar to an AHA or BHA — but it’s actually not. Ferulic acid is a very important antioxidant, helping to prevent free radicals from damaging your skin. It is a hydroxycinnamic acid that’s found in tea, coffee and red wine.

Other acids that you should be dropping — but not confusing with our AHA and BHA friends — are hyper-hydrating hyaluronic acid and skin-strengthening amino acids (like arginine and glutamine).

There are also fatty acids that cause additional confusion by appearing as types of alcohol, such as cetearyl alcohol, when they are not alcohols at all. Another kind of fatty acid is isostearic acid, used as a binder or surfactant in beauty products.


  • July 31, 2016

    by Marta

    That's a great question Aubrey. I think Kojic Acid qualifies as a bone fide. It isn't an AHA or a BHA, but it comes from fungi and has skin lightening properties (as AHAs do). More on it here:

  • July 30, 2016

    by Aubrey

    Is kojic acid also one of the faux acids?

  • July 27, 2016

    by Marta

    Hi John, your skin becomes more sensitive to sun and, therefore, potentially prone to burn. Secondly, there's irritation in an of itself. I recently tried a product with a high dose of glycolic acid and it stung my skin on application. People with sensitive skin can find strong AHA and/or BHA formulas irritating to their skin.

  • July 26, 2016

    by john

    Excellent and informative reading....Question: What happens to skin that has been treated with hydroxy acids and exposed to the sun? I didn't realize this and it appears my skin looks like a faint sunburn? Would this be the kind of irritation you mean? Thanks!

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