Despite the prevalence of acids found in a large number of makeup and skincare products today, the idea of putting acid onto your skin may still seem like an odd or worrying concept.
Alternatively, you may have read multiple marketing materials promoting hyaluronic acid as the ‘must-have’ skincare ingredient, or seen toners advertised with varying percentage levels of glycolic acid.
Either way, if you’re putting acids on your face, it’s important to know what benefits they bring, and if there’s anything to look out for or avoid so we’ve listed the most common acids – as well as detailed a couple of other important ingredients – in our guide below to demystify some of the current skincare trends.
You can also check out our Ingredient Spotlight series to learn more in-depth detail about the science behind many of these ingredients.
The majority of acids that have become commonplace in makeup and skincare fall within two main groups of compounds: Alpha hydroxy acids, known as AHAs, and Beta hydroxy acids (BHAs).
What are they? Alpha hydroxy acids come from a group of compounds that each contain one hydroxyl part (hydrogen next to oxygen) and a carboxyl acid part. In alpha hydroxy acids, these two parts are separated by one carbon atom. There are many types of AHAs used in skincare, and most are extracted from plants or animals.
Types of AHAs: AHAs include citric acid, glycolic acid, hydroxycaproic acid, hydroxycaprylic acid, lactic acid, malic acid and tartaric acid.
What are AHAs good for? AHAs are, for the most part, used for chemical exfoliation and reducing wrinkles. There has been more extensive research into the effects of glycolic and lactic acid compared to the others, which is why you’ll find them in more products compared to the others.
It should be noted that all AHAs can increase some people’s sensitivity to sunlight, so if you start to use AHAs in your skincare routine, make sure to use a product with SPF 30 or higher on your face. Read more in our What is SPF? guide.
Below we’ll explain a bit more what the most common AHAs do:
Glycolic acid is the smallest of all the AHA molecules with the chemical formula C2H4O3, and it is found in sugar plants. Because it’s small, it is easily absorbed into the skin, hence its popularity in skincare. It is used as an exfoliator because it works to remove dead cells, sebum, and protein that are clogging pores, making skin look brighter or more glowing. See our best toner article for more information.
Lactic acid is similar to glycolic acid, but slightly bigger, with the chemical formula C3H6O3. It is found in milk and is also produced in our muscles while exercising. If you’ve ever felt burning muscles during exercise, this is caused by an excess of lactic acid the body can’t get rid of quick enough. On top of having the same benefits as glycolic acid, such as exfoliation and evening skin tones, lactic acid is more moisturising than other AHAs.
FURTHER READING: Lactic acid for skin: What is lactic acid and what does it do?
What are they? In a beta hydroxy acid, the hydroxyl group is separated from the carboxyl by two carbon atoms instead of one. This means the molecular structure is slightly more complicated than an alpha hydroxy acid.
Types of BHAs: Salicylic Acid
What are BHAs good for? The structure of BHAs means they’re more soluble in oil, as opposed to water. This means they dissolve into the oils and sebum found in your skin, which allows them to go deeper into the skin. This also means BHAs exfoliate the underneath layers of your skin, while AHAs work on the top layers only.
There is only one kind of beta hydroxy acid that’s popular in skincare, compared to the many alpha-hydroxy acids (AHAs), and that’s salicylic acid. Once the acid has penetrated into your skin, it works by dissolving the bonds between skin cells and can help to treat acne, blackheads, and whiteheads.
You can read more about this in our salicylic acid guide, in which we also recommend a range of products that include the spot-fighting ingredient.
Of course, AHAs and BHAs are not the only types of acids found in skincare products, there are plenty of others but the two you may have heard about are hyaluronic acid and retinoids.
Hyaluronic acid is produced naturally in our bodies, and its function is to retain moisture.
There is a large amount of hyaluronic acid found in our eyes and connective tissues. As a result, hyaluronic acid is marketed as an ingredient to treat dry skin, helping the skin hold more moisture and look plumper.
Hyaluronic acid can be combined with many other acids, except glycolic acid which has a low pH level and could stop the hyaluronic acid from working. As always, be careful when combining different acids in your skincare routine, particularly if you have sensitive skin. You can read more in our in-depth What is hyaluronic acid guide, as well as our science of moisturiser article.
Any ingredient you see with the word retinol, retinoid or retinoic acid is a derivative of Vitamin A. Retinoids were first developed in the 1970s as treatments for skin problems and they have a number of science-based benefits.
READ NEXT: Best anti-ageing cream
Firstly, retinoids have been proven to unclog pores, for example, which can help make other products more effective. Retinoids are often said to be great treatments for signs of ageing, but just like AHAs they can make your face more sensitive to sunlight.
When starting to use any new acid, it is best to start with a lower concentration and build up. It’s easy to buy any of these products for reasonable prices. For example, The Ordinary sells retinoids from concentrations of 0.2% up to 2%.
FURTHER READING: What is retinol and what does retinol do for your skin?
You may have seen the words ascorbic acid written on the back of skincare and other products, but this is just the official name for the water-soluble version of Vitamin C.
When many of us think of Vitamin C, we tend to think of oranges and how good they are for our immune system. Yet Vitamin C has just as many benefits when it comes to our skin. It protects from UV damage, boosts your complexion, promotes a healthy natural glow, and reduces fine lines. You can read more about this in our skin food guide.
If you have dark circles or pigmentation, specifically, you’ll benefit from using Vitamin C on a regular basis. You’ll see ascorbic acid/Vitamin C in many dark spot correctors, for instance.
The chemical does breakdown quite quickly though, so we recommend you store any skincare that contains ascorbic acid/Vitamin C in the fridge. Check out our best skincare fridge list for recommendations to suit all budgets.
You can read more in our guide to the best Vitamin C serums.
Abigail is a leading science journalist writing about space, sustainability, technology and culture. She is author of The Art of Urban Astronomy, a must-have guide to the night sky that guides you through the seasons and learn about the brightest stars and constellations, the myths and legends of astronomy and how to identify star clusters and galaxies.