A Complete Guide to Acids in Skincare & Chemical Exfoliation

08 July 2022


So many acids, so little time.


Acids in skincare may be considered old-school by some beauty fans, but these evidence based, tried and tested active ingredients are making a comeback. One of the top active ingredients for healthier is to use acids for chemical exfoliation to get healthier skin. But before you get started on acids, here’s a guide to understanding the different types of acids (AHAs, BHAs and PHAs); how they work, how to use them safely and the best skincare pairings.


Here’s everything you need to know about acids in skincare.

What is an acid?


Back in chemistry class, we might have been taught that an acid is a substance with a pH below 7. In skincare products, acids refer mainly to alpha-hydroxy acids (AHAs) and beta-hydroxy acids (BHAs). In this sense, “acids” like hyaluronic and tranexamic acid are not the kind of acids that will be discussed in this review.


*These active ingredients have already been discussed in Everything You Need to Know About Hyaluronic Acid and Tranexamic Acid for Hyperpigmentation Explained.


A misconception among many is that acids in skincare are too harsh on the skin; or they can thin the skin. So here’s a beginner’s guide to understanding the different types of acids in skincare and how to use them safely.

Benefits of chemical exfoliation with acids in skincare and chemical peels


What are the benefits of using acids in skincare?


When applied to the skin, acids dissolve the connections that bind the top layers of skin cells together. By loosening these connections, the top most layer of dead skin; excess oil and dirt trapped in the skin fall away. This process is called chemical exfoliation.


Chemical exfoliation also allows for skin renewal; as newer and smoother skin emerges from underneath.


Some of the benefits of using acids in skincare are reduced hyperpigmentation, smoother skin texture and more even skin tone. If you have oily or acne, using acids in skincare allows for microexfoliation to reduce pimples and comedones.


Related blogposts:

Acne: Types, Causes, Treatments & Tips for Prevention 

Maskne: How to Avoid Acne from Wearing Surgical Face Masks


A simple guide to understanding acids in skincare


What are the different types of acids in skincare?


Acids differ in their depth of penetration of the skin and their strength. Broadly speaking, there are 2 main groups of acids: alpha-hydroxy acids (AHAs) and beta-hydroxy acids (BHAs).


Alpha-hydroxy acids (AHAs)

Of all the acids in skincare and chemical peels, AHAs are the most commonly used. There are different types of AHAs- and they differ in their molecular size and pharmacokinetic properties on the skin. Some examples of AHAs are: Lactic acid, mandelic acid, glycolic acid.


AHAs are water soluble, so AHAs work better on the surface of the skin. Conditions at the surface of the skin, such as hyperpigmentation and dull skin are best treated with AHAs. This exfoliating effect of AHA also evens out skin tone and smooths rough skin.


Related blogposts:

How to Lighten Hyperpigmentation and Dark Spots with Skincare

Hyperpigmentation Disorders: Types, Causes & Treatments


AHAs have humectant benefits; so they are less drying on the skin than their BHA counterparts. Also, AHAs are naturally occuring in nature- lactic acid is found in sour milk; glycolic acid is from sugar cane; and citric and malic acid are found in fruits. Because of this association, AHAs are sometimes referred to as fruit acids.


Beta-hydroxy acid (BHA)

The other main group of acid used commonly in chemical peels and skincare is beta hydroxy acid. Unlike AHAs, there is only one type of BHA: salicylic acid.


BHA is oil soluble so BHA binds to sebum in the pores and penetrates deeper into the skin than AHA. BHA also also anti-inflammatory benefits, if you struggle with  comedones (clogged pores) and acne, BHA can be beneficial. Salicylic acid can be absorbed through the skin; so be mindful not to use it in large amounts.


BHA use during pregnancy is also controversial and expectant mothers should consult their doctors before using salicylic acid.


Related blogpost:

Pregnancy Skincare Guide: What’s Safe and What to Avoid?



Poly-hydroxy acids (PHAs)

A relatively new addition (but not quite) to the acid scene in cosmetic products is polyhydroxy acids. Although PHAs may seem like a new entity of acids; PHAs are actually a type of AHAs. Some skincare brands also refer to PHAs as “second generation AHAs”. Some examples of PHAs are lactobionic acid, gluconolactone and galactose.


How PHAs differ from AHAs is in their molecular size. PHAs have larger molecular sizes than traditional AHAs, so PHAs are unable to reach deeper into the skin. The exfoliation and skin renewal effect with PHAs is less than conventional AHAs. However, the risk of side effects such as irritation or hypersensitivity is less with PHAs. Hence, users who have conditions where they are unable to tolerate AHAs or BHAs (e.g. eczema and rosacea) may benefit from using PHAs.



 L’oreal Paris is one brand that carries a comprehensive range of glycolic acid products from facial wash, serum, day and night creams and face masks.



How do I use acids in skincare?


With so many permutations of acids, combinations, concentrations and types of products, here’s a doctor’s guide to using choosing acids in skincare:


Type of acid in skincare

If you have oily skin or acne, BHA (salicylic acid) will be a better choice to get rid of the excess sebum and clogged pores. For dull skin and hyperpigmentation, AHAs are a better option. Lactic acid and malic acid are gentler on the skin, so they’re a safe starting point for beginners.


If you have sensitive or dry skin or conditions such as rosacea and eczema, PHAs are the gentler choice.


Concentration of acid in skincare

The effectiveness of an acid is partly determined by the concentration of acid. In most over the counter formulations in Singapore, the concentration of acid in the product is usually under 1 to 15%. The effectiveness of the acid improves as its concentration increases. However, higher concentrations of acid come with increased risks of side effects such as burns.


If you are new to acids, start with a lower concentration of acids in your product- perhaps 1 to 5%. By beginning with a lower concentration, you’ll be able to gauge your skin’s response to acids without incurring dryness, overt peeling and burns. If your skin tolerates this well, you can escalate the concentration of the acids in your product.


How often should I be using acids in my skincare routine?

How frequent you should be using acids will depend on your skin’s tolerance of acids. If you are new to acids, start using it once a day or once every 2 days with gentler acids (e.g. lactic acid, mandelic acid, PHAs) and increase the frequency of use if your skin tolerates well.


Choice of skincare product

You’ll find acids in all forms of skincare products- facial washes, toners, serums, moisturisers and even face masks! You can start by introducing acids into one of these product choices, say, a serum or toner. Pair this with a moisturiser to reduce dryness and irritation. Continue reading for recommended skincare pairings with aids!


If you’re afraid of leaving acids on your skin overnight or for an extended period of time, use acids where you can wash them off shortly. Facial washes and masks that contain acids are safer and gentler on the skin for this reason. I share my product reviews and recommendations in Review of Face Acids in Skincare.


dry skin


What are the risks of using acids in skincare?


Some of the side effects or complications of using acids on the skin include:

• Burns

• Dermatitis or rash

• Swelling

• Blisters

• Hyperpigmentation

• Irritation, itching, tenderness

• Increased sensitivity to sun exposure


The side effects of acids on the skin are affected by the type of acids used, concentrations of acids and duration of acids on the skin. Hence, if in doubt, start with gentler acids at lower concentrations and for short duration.


Find out the 4 reasons your skincare is not working here! Follow me on Instagram @drrachelho for more bite sized educational content.


What if I don’t see results from using acids in skincare? Alternatives to acids in skincare


If you’re not seeing the results from your skincare after being consistent with using it; you can consider escalating the acids if your skin tolerates well! You can progress to using stronger acid choices; higher concentrations and increasing the frequency of use.


If also, despite changing the acids you’ve used and results are lacklustre, you might want to consider seeing your doctor for a chemical peel. A chemical peel is a medical treatment that uses even stronger acids and at higher concentrations.


Related blogpost:

The Truth about Chemical Peels


For conditions such as acne and hyperpigmentation; additional treatments may be required on top more than acids in skincare and chemical peels alone for optimal results. In these instances, additional skincare and treatments such as Q-switched lasers may be recommended by your doctor


Related blogpost:

10 things to Know Before Getting Lasers for Hyperpigmentation


A chemical peel being performed in my clinic in Singapore.


How does using acids in skincare compare with chemical peels in a clinic?


In Singapore, chemical peels are medical treatments performed by a doctor. The choice of acids is tailored for the patient’s concerns and conditions; and the concentration of acids can range from 20% to 50%- absolutely not child’s play.


The results of a chemical peel performed by a doctor can be more obvious than at home chemical peel with skincare acids. However, the risks of side effects of burns with a chemical peel are also higher. In a clinic, the chemical exfoliation is much more controlled and the doctor can monitor the reactions of your skin before terminating the chemical peel.


Best skincare pairings with acids?


To combat any irritation from the acids in skincare- add actives that calm the skin and reduce inflammation. Examples of such active ingredients are niacinamide and cica.


Dryness is another common concern among many who use acid. Pairing acid serums or toners with moisturiser can help to ameliorate dryness. Hyaluronic acid is an effective and affordable ingredient that keeps the skin plump and moist; ceramide is another ingredient that strengthens the skin barrier.


Related blogposts:

Niacinamide: A Versatile Ingredient Your Skin Will Thank You For

Cica in Skincare: Centella Asiatica Explained

Everything You Need to Know About Hyaluronic Acid

5 Cult Favourite Hyaluronic Acid Serums Reviewed

Ceramides in Skincare: A Relief for Dry & Sensitive Skin



Using acids on the skin can also cause transient hypersensitivity to UV rays from the sun. This increases the risks of UV damage from the skin including sunburns and signs of premature aging in the skin such as hyperpigmentation. Sunscreen use (choose a broad spectrum one with at least SPF 30 coverage) is highly recommended if you use acids. More educational sunscreen posts can be found here:

Sunscreen Reviews 2021

Sunscreen Reviews 2019

Can Asian Sunscreens Be Trusted? The Purito-gate Controversy Explained

How to Prevent Sunscreen from Pilling


Lastly, one wonder antioxidant that pairs very well with acids in skincare is vitamin C! Vitamin C in its active form, L-ascorbic acid, functions best in an acidic environment. With acids on the skin, the skin’s pH dips to improve the efficacy of topical vitamin C. This only holds for activated vitamin C (L-ascorbic acid); and not for the inactive forms of vitamin C. You can learn more about topical vitamin C’s benefits and how to choose a serum in Topical Vitamin C: One of the Best Ways to Protect Your Skin.


Who shouldn’t use acids in skincare?


Ending off this blogpost with a word of caution for using acids in skincare. Using acids in skincare is a great way to get healthier and smoother skin; as well as reduce acne and hyperpigmentation. However, if you are experiencing any infection, sunburns or inflammation of your skin- hold off the acids until your condition recovers! If you’re using actives like retinoids; you might experience increased irritation, dryness and peeling if you use them with acids together. If in doubt about how to use your actives, it’s best to check in with your doctor.


Related blogposts:

The Beginner’s Guide to Retinoids

5 Affordable & Popular Retinoid Serums Reviewed 



1. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Kornhauser et al. Clin Cosmet Investig Dermatol. 2010; 3: 135–142.

2. Dual Effects of Alpha-Hydroxy Acids on the Skin. Tang and Yang. Molecules. 2018 Apr; 23(4): 863.

3. Clinical and cosmeceutical uses of hydroxyacids. Green et al. Clin Dermatol. Sep-Oct 2009;27(5):495-501.



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