How to Exfoliate 2: All About Chemical Exfoliants

aha-exfoliants

Here’s Part 2 of this skincare series on exfoliation. Part 1 was on physical exfoliating tools and scrubs, this time we’re tackling the more complex chemical exfoliants, before moving onto picking the right exfoliation routine for your skin in Part 3. For a simpler overview, you can head to this exfoliation basics post, and for a more user-friendly version check out my free exfoliation guide.

What’s exfoliation again?

Your skin is covered in a thin protective layer of dead cells (the stratum corneum) which naturally shed over time in a process called desquamation. Sometimes this layer gets too thick, resulting in dull, rough skin. Exfoliants help the shedding along, resulting in more even, “glowier” skin.

What’s chemical exfoliation?

Chemical exfoliants help cells shed in a more indirect way than physical exfoliation, which works using friction between the tool or scrub and the skin. The mechanism of how chemical exfoliants work aren’t always obvious, but the most common theories and methods of how they work are:

  • by normalising cell turnover – that is, how quickly cells in the epidermis die and migrate to the stratum corneum, pushing old cells out. Exfoliants do this by travelling to living cells under the dead layer and telling them to change how they behave – in more technical terms, they act on receptors to upregulate cell division. (Technically, any ingredient that does this is a drug, but regulations around these “cosmeceuticals” is pretty iffy.)
  • by unsticking the cellular glue (desmosomes) holding dead cells together in the stratum corneum.

Chemical exfoliation is touted to be gentler than physical exfoliation, mostly because it’s less prone to user error. However, how well it works depends largely on the formulation of the product. A poorly formulated product might not work, or it might work so well that it irritates your skin and causes uneven pigmentation and chemical burns.

Product categories

Click on each heading to jump to that section.

Leave-on Hydroxy Acid Products

Hydroxy acids are the most common ingredients in chemical exfoliants. There are two main types:

  • Alpha hydroxy acids (AHAs), which includes ingredients like glycolic acid, lactic acid, malic acid and mandelic acid. Glycolic and lactic acids are most common in skincare, and the vast majority of scientific studies on AHAs are based on the action of glycolic acid.
  • Beta hydroxy acids (BHAs), of which salicylic acid is the only one commonly used in skincare (I’ll be using the terms “BHA” and “salicylic acid” interchangeably).

A few ingredients are technically both alpha and beta hydroxy acids such as citric acid, which acts more like an AHA.

It’s not 100% clear how AHAs and BHAs work to exfoliate the skin – it’s likely to be a combination of the two actions described at the beginning: increasing cell turnover at the epidermis and unsticking stratum corneum cells. As well as just removing build-up of skin, they can also improve hyperpigmentation and reduce the appearance of wrinkles.

There are a few key differences between AHAs and BHA/salicylic acid:

  • Solubility: The commonly used AHAs (glycolic acid, lactic acid) are water soluble, while salicylic acid is oil soluble. Theoretically this means salicylic acid is better for treating oily skin and clogged pores because they can penetrate through sebum and sebum plugs, but there’s a lot of variation between people’s experiences. You’ll generally find AHAs in products for dry, ageing skin, and BHA in products for oily, acne-prone skin.
  • Sun sensitivity: Glycolic acid is documented to cause sun sensitivity for a while even after you finish using it, while salicylic acid isn’t. Salicylic acid has a UV protective effect while on the skin, due to the benzene ring in its structure which lets it act as a chemical sunscreen. You need to wear sunscreen while you use alpha hydroxy acids, and for at least a week after you finish – otherwise, you can actually cause more wrinkles and uneven pigmentation and sagginess than you started off with! And you should use sunscreen with salicylic acid anyway.
  • Other effects: Salicylic acid can have some anti-inflammatory action, depending on whether enough gets through the skin – it’s actually one of the active forms of aspirin. Glycolic and lactic acids are humectants that act to slow down the evaporation of water from the skin.

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How to Get Started on At-Home Chemical Peels

peels

peels

If you’re like me and you love chemical exfoliants but want to take it to the next level, then you might be interested in trying out some chemical peels. Dermatologists and some beauty salons perform all manner of peels, but you can easily and safely do light chemical peels at home.

What is a chemical peel?

A chemical peel involves applying a chemical on your face for a short period of time, which will kill the outer layers of skin. Once these layers slough off, you’re left with fresh skin. They can good for treating a smorgasbord of skin problems, like hyperpigmentation, wrinkles and acne.

Peels are usually classified by how much skin is affected – how deep does the peel go? We’ll be talking only about the most superficial peels here, because the deeper peels are dangerous to do at home. For more on the finer differences between different peel depths, see my earlier post on chemical peels.

Why do we need to exercise caution?

Chemical peels are controlled chemical burns. We’re talking about burning off your skin here – the chemicals we’ll be using can potentially blind you if they get into your eyes, or scar you permanently if you leave them on too long. Going too quick is particularly bad for people with darker skin – you can end up with post-inflammatory hyperpigmentation (PIH), which is where your skin gets dark patches after damage (if your knuckles are darker than the rest of your skin, you’re probably susceptible to this). Don’t let these warnings put you off though – with sensible safety precautions, you’ll be right as rain.

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