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guide to alpha hydroxy acid


Alpha hydroxy acids (AHAs for short) are a group of naturally occurring organic acids found in plants (especially fruits) or produced as a by-product of milk or vegetable fermentation. Although originally purified from such sources, the AHAs used in dermatologic and cosmetic skin care products today are usually synthetically produced.

AHAs have a long history of use as skin care ingredients, dating all the way back to ancient Egypt when sour milk was used to improve the skin's appearance. Although those Egyptians knew it worked, they didn't understand why - but we now know that lactic acid, an AHA, was the active compound in the sour milk.

In more recent times, the extensive study of glycolic acid during the 20th century revealed its potential as a chemical exfoliator, and its wide adoption for use in glycolic acid peels in the late 1980s helped bring AHAs into the mainstream skincare industry. Alpha hydroxy acids are now found in a range of cosmetic products including cleansers, toners, serums, and moisturisers, and are also employed at varying concentrations in professional treatments like chemical peels and hydrafacials.

Types of alpha hydroxy acid

There are multiple members of the alpha hydroxy acid family. Their varying properties offer subtly different chemical exfoliant benefits to suit different skin types and concerns. Below are some of the AHAs most commonly used in skin care products:

glycolic acid


Glycolic acid is found naturally in numerous plants and fruits including sugar cane, beetroot, grapes, green apples, and other fruit. Whilst all chemical exfoliants disrupt the bonds between cells and increase skin cellular turnover, glycolic acid has the smallest size molecule of all AHAs and is considered to have the greatest rate and degree of skin penetration. Shown to increase skin hydration in addition to providing exfoliation, skincare professionals often recommend this acid for concerns such as visible signs of ageing and sun damage. Studies also suggest topical glycolic acid can stimulate production of collagen.

lactic acid


Naturally occurring in sour milk, lactic acid offers gentle benefits that are generally tolerated by sensitive skin due to its larger molecule size limiting skin penetration. Lactic acid is also a component of the skin’s natural moisturising factor (NMF), supporting the benefit of lactic acid for skin hydration. Studies have also shown the value of using lactic acid for skin discolouration.


Present in citrus fruits like oranges and grapefruit, the exfoliating benefits of citric acid include promotion of skin cell turnover to smooth skin. Citric acid can also be used as a non-toxic preservative to protect the stability of skincare products and help balance their pH, or level of acidity.


Derived from apples and cherries or synthetically produced, malic acid has a larger molecule size than most other exfoliating alpha hydroxy acids. It therefore doesn't penetrate as deeply and is less likely to cause irritation in individuals with a sensitive skin type.


In addition to AHAs there's another group of naturally occurring organic acids called beta hydroxy acids (BHAs).

A key difference between AHAs and BHAs from a skin care point of view is that AHAs are water soluble acids and BHAs are oil soluble. This attribute enables a beta hydroxy acid to improve skin texture, dissolve sebum (oil) to help decongest pores, and target blackheads and whiteheads. BHAs are therefore especially beneficial for individuals with oily or blemish-prone skin and are appropriate for all skin tones as well as those with sensitive skin.

Like AHAs, beta hydroxy acids help improve the appearance of visible signs of ageing, including fine lines, wrinkles, dullness, and uneven skin tone, and can be found in cleansers, toners, serums, and moisturisers, as well as office-based chemical peels.

Beta hydroxy acids include salicylic acid and lipo-hydroxy acid (LHA) that provide cell-by-cell exfoliation and help promote skin cell turnover.

How do AHAs work?

In skin care terms, AHAs act as chemical exfoliants to help remove dead skin cells. They do this by weakening the bonds that hold dead cells to the skin's surface, making it easier for them to slough off. AHAs are also gentle enough to remove rough or flaky skin without causing discomfort.

Using AHAs can help improve texture by eliminating the build up of dead cells and bringing healthy, new skin cells to the surface. They can help improve rough, dry skin and keratosis pilaris (aka “chicken skin”), and reduce discolouration and blemishes. They also assist with smoothing fine lines and wrinkles.



AHAs can be a good alternative to physical methods of exfoliation, such as using abrasive brushes, scrubs, or face cloths. These methods of mechanical exfoliation can be harsh and cause discomfort, especially for individuals with dry or sensitive skin. In such cases exfoliation with a low strength AHA may be more suitable.


Removing the top layer of dead cells reveals fresh new skin which is brighter and more radiant. Skin care products formulated with alpha hydroxy acids also help promote skin cell renewal by increasing the rate of cellular turnover.


With long-term use, AHAs may also promote collagen and elastin production in the skin.

Collagen is a fibre-like protein that gives the skin much of its structure, and elastin is a coiled protein that (yes, the clue's in the name) gives skin its elasticity. Together they help keep your skin plump and smooth-looking. Production of these naturally decreases with age, and sun damage may also accelerate collagen destruction, resulting in sallow, sagging skin.

AHAs may help promote collagen production by breaking down old collagen fibres to make way for new ones. By using AHAs regularly, people may notice their skin looks plumper.


As we age, and with exposure to sun, the turnover of new skin cells slows down. This can increase the appearance of fine lines and wrinkles. By increasing the production of collagen and elastin, surface lines and wrinkles are smoothed.


The likelihood of skin discolouration also increases with age and sun exposure. Because new skin cells are evenly pigmented, encouraging the turnover of old, discoloured cells through regular use of AHA products may help to reduce the appearance of hyperpigmentation or dark marks on the skin, such as:

● age spots (the flat brown spots that tend to develop on hands and face)

● sun spots

● post-blemish marks

Dermatologists often use AHA peels for these purposes, as they can work on deeper layers of the skin than over the counter (OTC) products.

It's important to note that in darker skin, AHAs can cause dark spots and changes in skin tone.

AHA products in the SkinCeuticals range

Simply Clean Makeup Removal Cleanser: ideal for normal, combination, and oily skin, this gel-based cleanser contains an AHA blend for gentle exfoliation of dead skin cells to reveal softer, smoother skin—and it effectively removes long-wear and waterproof makeup.

Blemish and Age Cleansing Gel is a targeted exfoliating cleanser suitable for ageing, combination and oily skin types, featuring a blend of both AHAs and BHAs (lipo-hydroxy acid, glycolic acid, and salicylic acid). Formulated for ageing, mild acne-prone skin, this deep cleansing gel gently refines the appearance of congested pores and helps to reduce blemishes without drying the skin.

Blemish and Age Toner: a targeted clarifying toner ideal for combination or oily skin. Formulated with the same triple combination of exfoliating agents as the cleansing gel; the AHAs glycolic and lipo-hydroxy acids, plus BHA salicylic acid, it helps clear clogged pores and remove dead skin cells from the surface. Designed for ageing, acne prone skin, this clarifying toner has a low pH to efficiently exfoliate skin cells, revealing more even, refined, and brighter skin.

Glycolic Renewal Foaming Facial Cleanser: a high-concentration cleanser formulated with 8% glycolic acid combined with 1% phytic acid, aloe leaf juice and glycerin as other active ingredients. This cleanser helps exfoliate rough skin to deliver a smoother and brighter complexion while removing excess oil, dirt, debris, and long-wear makeup without stripping the skin of moisture.

Glycolic 10 Renew Overnight Cream: a glycolic acid exfoliating cream for night time. Stimulates skin cellular turnover to improve the appearance of skin texture and tone for a brighter complexion and radiant skin. This scientifically developed cream with 10% glycolic acid is synergistically blended with 2% phytic acid and a triple action comforting complex to help support the skin barrier.

Blemish + Age Defence Serum is an oil-free face serum for ageing, mild acne-prone skin prone to blemishes. This acid blend combines 2% dioic acid to reduce excess sebum production, plus a combination of salicylic acid, citric, glycolic, and lipo-hydroxy acids to reduce blemish formation and decongest clogged pores, while improving the appearance of fine lines and wrinkles, blotchiness, blemishes, and uneven skin tone.

The importance of sun protection when using AHAs

Alpha hydroxy acids help minimise the build-up of dead skin cells on the skin's surface to reveal radiant, healthy-looking skin—but this exfoliation can leave the skin more vulnerable to UV damage from sun exposure. Likewise, BHAs also cause increased sun sensitivity.

Applying a broad-spectrum sunscreen should always be the final step in any skin care routine, but it’s especially important to use sun protection daily when using a chemical exfoliant.

Frequently Asked Questions

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