The Skincare Series:
3. AHAs, BHA and Other Acids

Now that you have the acid basics down, let's discuss specific acids. We will cover specific characteristics of several of the AHAs plus BHA, Alezaic acid, Ascorbic acid (vitamin C), and Hyaluronic acid. Information about how to actually apply these to your skin will be in Part 5.

Remember that most of these acids are also skin irritants and may increase your skin's sensitivity to sunlight. If you missed the Skin Threshold and Sunscreen discussions in Part 1 of this series, I encourage you to read those now.

I favor The Ordinary's products because of their high quality and low price. Still, you can find the ingredients below in products from many different manufacturers. When available, I provide links to The Ordinary's website for specific products.

The AHAs

AHA's (alpha-hydroxy acids) are actually a group of acids with useful skin properties. Here's how a chemist would think of them (these are called 'skeletal' diagrams):

Skeletal diagrams of AHAs

We won't be talking about all of these! All of the AHA's are exfoliants. Also, depending on the particular AHA you are using, you can get the following benefits:

  • Increased collagen
  • Increased production of new cells
  • Reduce fine lines and wrinkles
  • Prevent acne
  • Fade hperpigmentation
  • Increase skin thickness
  • Even out skin tone and texture

They also help to keep the skin moisturized. Let's talk about a few in detail.

Glycolic Acid

This is the most popular of the AHAs and can be found in multiple products. As you can see from the chemical drawings, it is also the smallest of all the AHA molecules. This allows it to penetrate more deeply into your skin, but this also increases the risks of side effects such as skin irritation. It is also used (often with other AHA acids) in high concentrations as a peel or mask. It is by far the most studied of all the AHAs.

Best for:
Exfoliation, fading pigmented skin
Harshest of all the AHAs
Available from The Ordinary:
Glycolic acid 7% Solution, 240 ml, $8.70

Lactic Acid

This is the second most researched AHA after Glycolic Acid. It is known for being gentler, more hydrating, and more effective at treating sun-damaged skin. It also increases the ceramides in your skin. Ceramides are one of the three oil lipids that are important in keeping your skin waterproof, so lactic acid can help keep your skin hydrated.

People sometimes recommend yogurt masks because yogurt contains lactic acid. Unfortunately, the concentration of lactic acid in yogurt (1% or less) is too low to make this practice truly useful.

Best for:
exfoliation, fading pigment, moisturizing
The Ordinary sells two different concentrations of Lactic acid:
5% Lactic Acid, 3o ml, $6.50
10% Latic Acid, 30 ml, $6.80

Mandelic Acid

Mandelic acid has only been studied for its use in peels. If you take a look at the skeletal drawing above, you can see it's a much larger molecule and therefore much less penetrating and therefore gentler. It is very often recommended for people with bronze-ebony skin who find they are susceptible to rebound pigmentation (which is when an irritating treatment makes your skin more pigmented).

Best for:
exfoliation in darker skin
Availble from The Ordinary:
10% Mandelic acid solution, 30 ml for $6.80

Other Acids


There is only one BHA, and that is Salicylic acid. This is a widespread ingredient and is structurally related to aspirin, with whom it shares anti-inflammatory properties. Like the AHAs, it is an exfoliant. It is also found in wart and corn removers and very, very common in skin cleansers.

It is a big molecule and quite oily. Perhaps because of this, salicylic acid's effects seem less influenced by pH. Typical concentrations are 0.5-2%.

You can buy Salicylic acid masque's from The Ordinary, but I prefer to use it in a cleanser (see Part 1 ) and in combination with multiple AHAs as a peel (see, for example, my personal skincare routine described in Part 5.)

Azelaic Acid

This is a crucial ingredient in lots of prescription-only acne creams. It's very often prescribed for pregnant and nursing women as it's very safe. And pregnancy-associated acne is real. It's usually found at concentrations of 15-20%. Side effects are unusual unless you have very sensitive skin. If you do, you may experience redness, peeling, and stinging.

You can use azelaic acid to treat post-inflammatory hyperpigmentation (PIH). These are the dark spots that are left after a skin injury, such as acne. PIH is very common in darker skin. Hydroquinone is a kind of bleach that is often used to treat PIH, but there have been some recent concerns about its safety. If you are worried about hydroquinone, Azelaic acid, combined with retinoic acid, is almost as effective and perhaps safer. Azelaic acid has anti-inflammatory properties that have been known to improve rosacea. Rosacea can come in multiple forms. Azelaic acid does not work for inflamed vessels, but it will work for lumps and bumps.

Best for:
treating acne, including pregnancy-associated acne, fading pigmented areas. Helps with rosacea.
Mild. Safe for pregnant and lactating women.
Available from The Ordinary:
10% Azelaic acid suspension. 30 ml for $7.90

Ascorbic Acid

The most common and most studied water-soluble form of vitamin C. It has multiple benefits: treating pigmentation, increasing collagen. It's an anti-oxidant, so it protects against damaging free radicals that come from UV radiation and pollution. Free radicals are leading causes of skin aging.

The biggest problem with ascorbic acid is that it breaks down in water very quickly. This can be slowed by combining it with things like Vitamin E and ferulic acid, but these ingredients add a lot to the cost of the product.

My sweetie Dr. Davey recommends adding this last (if at all) to your skincare routine. The reason for this is that it is quite acidic (pH of 2-2.5) and at the same time less effective than things like Retinol and the AHAs. Sweetie Dr. Davey also believes Ascorbic acid is less effective for PIH than Hydroquinone.

Best For:
treating pigmentation, increasing collagen, fighting free radicals that cause aging.
Recommended Use:
Try other acids first.

Hyaluronic Acid

Hyaluronic acid is a very hyped ingredient. I am writing about it here primarily for that reason. It occurs naturally in your body. It is a primary ingredient in many dermal fillers, which are used to increase the size of your lips, cheeks, or other areas of your face.

Its acidic properties have nothing to do with its use in skincare formulations. It is too large a molecule to penetrate very far into your skin and is not an exfoliant. However, it is a remarkable humectant (hydrator) of skin. One gram of hyaluronic acid can hold onto six-liters of water! There are plenty of other suitable humectants (such as vaseline), but they may not feel as nice. They also lack the hype factor.

There is no reason to avoid products containing hyaluronic acid. But it is also no reason to purchase one. If a product containing hyaluronic acid is interesting to you for some other reason, by all means, buy it.

That's it for now. In Part 4, we will talk about the gold standard of skin care acids! Don't miss it! Meanwhile, if you have comments or questions, please send the nice ones to me! To do that, you can