Skin School: Every type of skincare acid, explained

Know your lactic acid from your salicylic? Check out our definitive guide to the different types of skincare acids and how they can transform your skin...

Acids are hard-working skincare ingredients that are often used for exfoliation and hydration. They can be categorised into two groups: alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs). Both dissolve the glue-like substance that binds dead skin cells onto the surface of the skin, allowing them to wash away, which leaves you with a smoother, brighter complexion. 

Some exfoliating acids have the ability to clear ‘cellular debris’ within the pore, so they work right into the deepest layers of the skin too and have an anti-bacterial effect, while others are known to increase hydration, collagen production and improve hyper-pigmentation. Here’s a breakdown of the acids you need to know…

Alpha Hydroxy Acids (AHAs)


Glycolic acid is derived from sugar cane and is the most well known and widely used alpha hydroxy acid. It is a favourite at Kate Kerr London as it targets both the skin’s texture and tone. The sugar acids dissolve the bonds that hold the dead skin cells onto the surface of the skin revealing younger, plumper cells. Exposing these healthy cells ensures that light is reflected rather than absorbed for a brighter complexion. 

Glycolic acid is also known for helping reverse sun damage and pigmentation and is thought to stimulate the growth of collagen and elastin. The downside of glycolic acid is that it can be particularly irritating so begin with caution and slowly increase your application frequency to find your skin’s tolerance.  


Citric acid, derived from oranges and lemons, is often used in skincare to help make a product more acidic for optimum function. Citric acid provides a thin film on the surface of the skin, which helps to prevent moisture evaporation, therefore enhancing skin hydration. It’s best to avoid citric acids in high strengths as they can cause undetected, low-grade inflammation in the dermis leading to the breakdown of healthy collagen and premature ageing.


Derived from apples, malic acid is a gentle alternative to glycolic acid and has multiple benefits. It’s not only beneficial to the skin for its exfoliating and brightening purposes, it’s also an effective antioxidant that fights free radical damage. For those who suffer from hyper-pigmentation, it can be a safer option as it’s less likely to cause inflammation, which can exacerbate the problem by causing post-inflammatory pigmentation.  

Malic acid is also a great acne treatment because it effectively clears out the opening of the pore to encourage the flow of sebum. This prevents the formation of comedones (those small flesh-colored acne papules), which can cause the skin to break out. 


Lactic acid, sourced from sour milk, is becoming increasingly popular and is another gentle alternative to glycolic acid. It shares a lot of the same benefits as glycolic acid and has actually been shown to be more effective at treating hyper-pigmentation. It’s much more easily tolerated and can even be used on pregnant women with permission from a doctor.

Beta Hydroxy Acids (BHAs)


Salicylic acid is extremely effective at treating both acne and ageing, whilst providing an anti-inflammatory action. With adult acne becoming more of a problem, having this dual action of targeting both acne and ageing is extremely beneficial. Acne has four contributing factors – an over-production of oil, a build-up of dead skin cells, an invasion of the acne bacteria and inflammation. Salicylic acid targets all of these factors, which is why it is a key component in my anti-acne treatment programmes.  

Not only does salicylic acid exfoliate the surface of the skin, it also has the ability to exfoliate within the pore itself to help prevent comedone formation.  This BHA is also known to stimulate collagen production and improve barrier function, protecting the skin and preventing water loss to help maintain skin hydration. Unfortunately salicylic acid can’t be used during pregnancy or breastfeeding. 


Hyaluronic acid is an absolute must in everyone’s skincare regime.  Holding 1000 times its own weight in water, it’s a natural humectant, meaning it attracts and binds water to provide a hydrating and plumping effect to the skin. The best thing about a hyaluronic acid serum is that it doesn’t upset your skin’s natural moisturising factors and therefore won’t make your skin sluggish and dry like many moisturisers can. It is great for all skin types and doesn’t cause any problems for oily or acne-prone skin.  

At home or professional strength: which is best for you?

Both at-home acid products and professional-strength peels can give great results – as long as you choose the right one for you. The main difference between the two is their level of intensity. At-home peels usually have about 10 percent (or less) AHA or BHA, while professional formulas can contain up to 70 percent.

The higher concentration allows facial clinicians to reverse more significant sun damage and fine lines. The longer the duration that the peel is left on the skin and the stronger the concentration, the deeper the peel penetrates. A series of three or four professional peels can lighten dark spots and soften roughness with minimal downtime. Check out our Advanced Skin Peel treatment to find out more.

Best acid for…

Dry skin? Lactic acid

Acne-prone skin? Salicylic acid

Ageing skin? Lactic acid; Glycolic acid

Dull skin? All

Sensitive skin? Lactic acid; Salicylic acid; Malic acid

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