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A beginner’s guide to direct acids

What are direct acids and what & they used for?

Skin cells are held together by epidermal lipids (oil soluble compounds) and special bonds. Exfoliation is a natural process by which specialised skin enzymes break down those bonds, shedding dead skin cells from the outermost layer of the skin. However, this process may not occur at an ideal speed, leading to an accumulation of dead skin cells on the surface of the skin – giving it a lacklustre appearance, causing congestion and leading to texture irregularities.

Chemical exfoliation helps to slough off dead skin cells through the use of hydroxy acids. They do so by softening, separating and promoting the natural shedding of dead skin cells. There are two types – alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs). AHAs are water soluble and gentle, as they mostly facilitate exfoliation at the surface level. BHAs are oil soluble and thus able to exfoliate deeper within the walls of pores to reveal visibly clearer looking skin.

How to choose the best acid exfoliant

When it comes to AHAs, the most popular ingredients used in skincare are glycolic, lactic and mandelic acids. These have a similar mode of action, but differ in molecular sizes, providing distinct levels of exfoliation.

Glycolic Acid 7% Toning Solution

The smallest of the AHAs, Glycolic Acid provides a great exfoliating effect at surface level for radiant, smoother skin. Additionally, studies comparing AHAs in order to improve the appearance of uneven skin tone and pigmentation have shown that glycolic acid performs best.

Lactic Acid 5% + HA 2%

This mild acid has a great ability to bind onto water and can also be found within the skin as part of the Natural Moisturising Factors (NMF), a mixture of compounds responsible for maintaining skin
hydration. For this reason, and besides being able to improve the appearance of pigmentation, age spots, and other factors that contribute to a dull and uneven complexion, lactic acid also supports skin hydration.

Mandelic Acid 10% + HA

This is the AHA with the largest molecular size provided by The Ordinary, allowing it to penetrate the skin at a slower rate, which in turn makes it very gentle and suitable for all skin types. The mildness associated with mandelic acid does not compromise its great exfoliating power, as well as its ability to effectively target uneven skin tone and dullness.

Salicylic Acid 2% Masque

In skincare, BHA will mostly refer to salicylic acid, an oil soluble compound that has the ability to penetrate the skin’s epidermal lipids, thus delivering exfoliating benefits within pores that may be congested. This ingredient is ideal for those with a visible excess of sebum production and blemishes.

How and when to use

Different products containing AHAs/BHAs should not be used in the same routine. Building up tolerance is advised for first time users, as well as patch testing prior to use. Some exfoliating products may be used daily (The Ordinary’s Glycolic Acid 7% Toning Solution, Lactic Acid 5% + HA and 10% + HA and Mandelic Acid 10% + HA), both AM or PM, but first-timers/those with sensitive skin might want to introduce acids to their routine a few times a week to start with, preferably at night. The Ordinary’s AHA 30% + BHA 2% Peeling Solution and Salicylic Acid 2% Masque should be used no more than twice a week and ideally in the PM; apply for the recommended time and rinse-off, following with a skincare routine that contains no other exfoliating acids.

Azelaic Acid Suspension 10%

Azelaic Acid is not an AHA or BHA. Instead, it is a naturally occurring dicarboxylic acid found in grains. Its exfoliating effect is much milder than that of hydroxy acids, but it has been shown to brighten the skin tone and reduce the look of pigmentation, while visibly improving the evenness of skin texture and reducing the appearance of congestion. It has also been successfully used to reduce the look of redness.

Azelaic acid can be used twice daily, AM/PM, after water-based products and before oils and creams. Please avoid peptides/EUK 134 0.1% and ensure daily application of SPF.

Taking care of your skin

Sun protection

As exfoliating acids are known photo-sensitisers, direct sun exposure should be avoided and sun protection must be applied every morning, even when limiting the acid’s application to night time only.


Due to their acidic pH, direct acids should also not be combined with products containing peptides (The Ordinary’s “Buffet”, for example), as these may be compromised in an acidic environment; the same applies to The Ordinary’s EUK 134 0.1%


Finally, it might be a good idea to separate direct acids from other activities that require the user to build up tolerance to the ingredient, such as retinoids and strong vitamin c (ex. Our 23 and 30% suspensions). Using them in different routines is a great option for first time users/sensitive skin types.

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