hydroxy acids

Hydroxy Acids Explained

What you want is smooth, even and dewy skin, but what you see in your mirror after a long winter is dull and lacklustre reflection. With summer just a few warm breezes away, help is at hand. Meet hydroxy acids. By Vivienne Parry
10 Aug 2020

What are hydroxy acids?

There are several types of hydroxy acids which you’ll know better as the active ingredients of skin peels.  AHAs (alpha hydroxy acids) are found throughout nature and their names tell you their origin.  So-called fruit acids include citric acid from citrus fruits, malic acid from apples and tartaric acid from grapes. Glycolic acid comes from sugar cane whilst lactic acid is from milk.  

BHAs (beta hydroxy acids) are a different, stronger form of hydroxy acids.  Salicylic acid derived from willow bark is the classic example.  At the other end of the spectrum are PHAs (poly hydroxy acids), which are the gentlest.

All have different uses and properties and can come in prescription and cosmetic grades of varying concentration.


Top tips

It’s better to use one product (whether containing a single hydroxy acid or a combo of them) rather than several types of products each containing AHAs (e.g. a wash plus a cream). Your skin will get the most from acids in your 20s and 30s, minimising fine lines, evening tone and repairing sun damage. After 40, retinoids are more appropriate.


How do hydroxy acids work?

New skin cells are constantly being formed in the epidermis and pushed upwards towards the surface where they are shed as dead cells. Removing the top layer of cells reveals new cells – a bit like removing dirt from a window makes glass gleam.  Whilst exfoliation with scrubs does the job, it’s the equivalent of cleaning a window with a fierce pan scourer causing scratches and damage. Dermatologist Dr Anjali Mahto is clear. ‘If you over exfoliate, you risk soreness.  This is especially the case for those with dry skin or skin conditions like rosacea.’ 

Scrubs are brute force removal. Hydroxy acids essentially dissolve the ‘glue’ that keeps the dead cells attached to the living layer below.  This seems to trigger skin cell renewal providing long term benefits in skin firmness, elasticity and reduction of lines as well as increased collagen production resulting in plumper skin.  They can also have an anti-inflammatory effect.  Finally, some are humectants, which means that they are water magnets, attracting water to the skin from the atmosphere.


How to choose your AHA?

Concentration and exposure time are the two key points to consider.  Over the counter AHAs contain concentrations between 4 – 18%, whilst professional clinic versions contain between 20-70%. ‘There’s some truth in higher concentrations being more effective’ says Dr Mahto.  But the insider knowledge here is that pH is all.  Too much free acid causes redness and flakiness, whilst too little does nothing. Formulators effectively use pH to control free acid values. pH should be between 3 and 4, although packaging won’t always tell you this.

If you use a product containing AHAs that you wash off within a few minutes, it’s unlikely to have much of an effect as AHAs take time to penetrate. But if you leave on AHAs too long, you can cause serious damage, which is why strong acids are prescription only, with rigorous control of application.

Hydroxy acids can be used in combinations, but choose carefully, ideally something where that combo has been clinically tested.

Peeling increases the sensitivity of skin to light.  We hope you’re using a daily sunscreen anyway, but if using an AHA peel, you MUST, MUST, MUST use a high factor sunscreen during the day to reduce the risk of skin damage.

Glycolic acid

Glycolic is a great choice for a peel. Why? Because its molecule is the smallest of all the AHAs and therefore penetrates the skin easier than any other AHA.

‘Glycolic acid suits most skin types’ says Dr Mahto ‘but I would caution its use for those with skin conditions such as rosacea or psoriasis as well as for those with very mature or dry skins’.


  • 10% concentration
  • low pH formulation
  • Ideally products for night use   

Salicylic acid

‘Salicylic acid is better for those with oily, acne prone or blemished skins, where breakouts, enlarged pores or blackheads are your focus.’ says Dr Anjali Mahto. BHAs actually penetrate pores, so they are very effective for these conditions.  They can be a cause of dryness, but don’t have the same photosensitivity problems of AHAs – but you should still be rigorous about sunscreens during the day because there is increasing evidence of UV interactions with pollution causing increased acne outbreaks.


  • 1-2% concentration
  • Ideally for night use
  • Don’t forget to moisturise

Dr Mahto again provides a note of caution ‘The skincare routine here (with cosmetic skincare products) is fine, but if you’ve still got problems with your skin which are not improving, you need more targeted advice’.


This article is intended as general information only. You should seek advice from a professional before starting any new regimen or course of conduct.

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