Alpha Hydroxy Acids

Paula's Choice ResistAlpha Hydroxy Acids (AHAs) are a certain type of acid typically found in foods like sugar and citrus fruits. They are often used in chemical peel products and chemical exfoliants, as well as various other skincare products.

AHAs are purported to be effective products for skincare, claiming to reduce fine lines, brighten the skin, and improve skin tone, but are they legitimate or B.S.? Let’s take a look…

What Are the Different AHAs?

The two most common alpha hydroxy acids are glycolic acid (derived from cane sugar, think “glucose”) and lactic acid (derived from sour milk, think “lactose”). Although these are the most common AHAs, they aren’t the only ones.

Tartaric acid, mandelic acid, malic acid, citric acid, gluconic acid, and several synthetic variants are just some of the others you may encounter.

The main difference between these acids is the molecule size, hwhich affects how quickly they work, how deeply they penetrate the skin, and therefore the extent of the effects you can expect to achieve with them[1].

What Do Alpha Hydroxy Acids Do?

AHAs work by exfoliating the skin – in other words they strip off the uppermost layer of skin to reveal the fresher skin below. It is often said that the acids destroy the bonds (a lipid “glue”) holding dead skin cells together, allowing them to shed off at a faster rate than what would happen naturally if you didn’t use them. But further research has shown that it’s not quite so simple – as explained by

According to research published in the Journal of Biological Chemistry, AHAs work by interacting with a membrane protein in the skin cells. They tested glycolic acid and found that it enters into keratinocytes and generates free protons. The acidic conditions activates an ion channel in the cells membrane protein which leads to a flow of calcium ions into the cell which ultimately leads to cell death due to it becoming overloaded[2].

As mentioned, the main difference between the different acids is the molecule size, which determines how deeply and easily the product can penetrate the skin. The smaller the molecule size, the better the results, with a trade-off of more irritation.

What about anti-aging? There is good evidence to suggest that AHAs produce a good anti-aging effect by boosting collagen and dermal firmness[3], and increasing the rate of cell renewal to a level equivalent to a 30 year old[4].

As for acne, AHAs have been shown to be effective. But at the same time, salicylic acid (Beta Hydroxy Acid) of equal concentration has been shown to be not only more effective for this purpose, but cause less side effects too[5].

For general skin appearance, you will find that your pores appear to be minimized, and your skin will take on a better tone. Acids can also reduce hyperpigmentation (often referred to as “lightening”, although these products do NOT bleach your skin or make you whiter than your DNA determines you to be).

Here’s a summary of the different acids and what you can expect from them:

Glycolid Acid

Glycolic acid is perhaps the “main” alpha hydroxy acid and the one most people will be familiar with. It is also the most effective due to its small molecule size, which allows it to penetrate fairly deep and easily into the skin. This can be a blessing or a curse depending on the sensitivity of your skin. If your skin is not very sensitive, it stands to reason that glycolic would be the best choice to get the greatest effect.

Glycolic before and after
Here is a before and after I found on This result was achieved using 40% glycolic acid, which is high in strength. It’s important to note that there is a difference in lighting between the before and after – however, the improvement appears clear.

Lactic Acid

Lactic acid has a larger molecule size, which means that while it doesn’t penetrate into the skin as easily, it also isn’t as harsh. For those with sensitive skin, you could use lactic acid to get results and exfoliation without the irritation.

Despite being a larger molecule than glycolic acid, studies[3] have shown that lactic acid concentrations of 12% can increase the firmness and thickness of the skin (both the upper epidermal and lower dermal layer). Lower concentrations of 5% appear to produce no dermal effects but do work on the epidermis, which is your topmost layer of skin.

Lactic acid has also been shown to improve the skin’s barrier by increasing the production of ceramide[6], though as far as I am aware there are no studies into the effectiveness of other acids for this purpose (so they may all perform this function).

Other Acids

Other acids such as mandelic acid with even larger molecule sizes tend to be the least effective, but also the least irritating of the bunch. Mandelic acid is not suitable for people with nut allergies.


A lot of skincare products these days combine a number of different acids into one. The idea is to include superficial layer acids with deeper penetrating ones such as glycolic acid so the glycolic can penetrate easier.

Some blends will also mix AHAs with BHAs (Beta Hydroxy Acids). A well known commercial example of this would be the Obagi Blue Peel Radiance, which is mainly BHA-based (20% salicylic acid), but also contains a small concentration of glycolic and lactic acid. The concentration of the AHAs is very small at only 2%, but that’s just one example.

As another example, MakeUpArtistsChoice sell a combination product of 15% mandelic acid with 15% salicylic.

Effects by Concentration

Sometimes it is said that lower concentrations of acid (under 8%) don’t offer any benefits[6]. However, you can still see an improvement in the appearance of your skin, since lower concentrations of 5% lactic acid have been found to positively affect the epidermis[3].

Medium concentrations such as 12% lactic acid can provide deeper effects, improving the firmness of the dermis.

Higher strength peels can be risky to use at home if you do not research how to use them safely and responsibly. MakeUpArtistsChoice provide good instructions along with their peel products. Higher strength acids absolutely must be washed off, and not only this, but an alkaline solution should be applied on top once the treatment is complete. Alkaline liquids neutralize acids and prevent them from working.

A Note on “Peeling”…

If you’ve only heard a little here and there about peeling, you may assume that peeling involves looking like a zombie for a week, with horrible patches of skin, scabbing, and so on. This is a misconception caused by the effects of very powerful acids such as TCA or acids in very high concentrations (or high concentrations left on for too long). With most peel products which contain acids in reasonable strengths, you can expect none of that. Most of the time you will just see flaking (to varying degrees), or even nothing at all.

Just because you do not visibly peel or flake, it DOES NOT MEAN that the product isn’t working.

What’s the Evidence?

As well as a wide range of anecdotal reports from happy users of AHAs on skincare communities across the web, many scientific studies have been carried out into the effectiveness of alpha hydroxy acids. These studies looked into several important factors including changes in dermal thickness, cell turnover, and collagen production.

What You Need to Know…

  1. Check the pH of the products you buy. The lower (more acidic) the pH of a product is, the stronger it will be in comparison to higher pH products.
  2. For best results, the smaller the molecule size the better, so try to use glycolic acid if you can. Irritation might occur, but the results will be much better if you can handle it. Acids which don’t penetrate as deep aren’t likely to give you the changes we all ideally desire, but could still improve the “glow” of your skin.
  3. Not all concentrations are good to use every day. As an example, for glycolic acid, 10% would be considered the highest strength for daily use. You want to give your skin time to rest and repair instead of keeping it in a constant state of inflammation.

    If you want something you can use every day there are milder options like Nip+Fab’s glycolic fix extreme night pads (5% glycolic) which I currently use myself. I find them very convenient to use and for me, the positive change in skin tone is extremely obvious.
  4. Layering products of different concentrations does not have an additive effect. 5% on top of 10% does not equal 15%, but rather averages out to 7.5%. This is because concentration is based on the amount of acid present in a given amount of liquid.
  5. Do not use products which are derived from sources you are allergic to. For example, avoid lactic acid if you are lactose intolerant.
  6. While retinoids work to thicken up the skin, they may also thin the top layer. Using chemical exfoliants and peels with retinoids may lead to overexfoliation if you are prone.



Alpha Hydroxy Acids really work, and aside from plenty of anecdotal evidence and before and after pictures taken at professional clinics, there are a lot of studies to back up their effectiveness. Are they going to make you look 10 years younger by themselves – well, no. But you can expect a definite improvement in your appearance with responsible regular use (assuming the acid concentration and pH level is ideal) so they should absolutely be a part of your arsenal.

Keep in mind that while lines and wrinkles may be the most obvious signs of “bad” skin when we look in the mirror, you would be very surprised at how much difference to your appearance a more even and healthy skin tone makes, and AHAs are worth it for just that property alone.

In my opinion AHAs are up there with Retin-A and vitamin C in terms of topical products that we know make a difference.

What to Look for in a Product

Buyer beware, not all AHA products are legitimate. Some are not ideal, or downright useless in a worst case scenario. So what should we look for to ensure the products we choose aren’t B.S.? The following is a good place to start:

  1. Look for products with a pH of 3.0 or below, and no higher than 4.5, as the acid is essentially neutralized at that point. A lower pH = a stronger product, so 10% glycolic at pH 2.0 is stronger than 10% glycolic at pH 4.0.
  2. Make sure the product you are choosing contains a suitable concentration to achieve the results you want. Higher concentrations will give a more dramatic result at the cost of more signs of irritation and possibly actual peeling of the skin.
  3. Be wary of AHA products which also contain vitamin A or any form of retinoid. The pH at which these two ingredients work conflict.

Here are some of the best-rated AHA products out there, sourced from recommendations on popular online skincare communities like Reddit’s SkinCareAddiction and the SkinCareTalk message board:


Cosrx AHA 7 Whitehead Power Liquid – This product contains 7% glycolic acid. I’ve seen it recommended frequently on SkinCareAddiction.

Paula’s Choice Skin Perfecting 8% AHA Gel – This product contains a slightly higher concentration of glycolic acid at 8%. This is another product I’ve heard a lot of users recommend on SkinCareAddiction.

Because some sources claim 8% is the minimum level to use[6], I would recommend this product over lower concentrations to be on the safe side. However, my skin is very tolerant, and for those with more sensitive skin you may find higher concentrations irritating with daily use.


The Ordinary Lactic Acid 5% + HA 2% – Here’s a mild peel that will work on the superficial layer of skin only. You should not experience visible peeling, but will see an improvement in the top layer of skin.

AmLactin 12% Moisturizing Lotion – If you remember that study referenced a few times throughout this article[3], 12% lactic acid was sufficient to cause changes in the lower dermal layer of skin. Essentially this product will give you a more “real” effect than superficial 5% LA peels, and can be used daily if your skin tolerates that frequency. Although I’ve seen this product recommended on both SkinCareTalk and SkinCareAddiction, the pH is too high for exfoliating effects. You can try it based on the testimonials of other users, but I would say you might not get the “full” AHA effect.

Unfortunately I am unable to find any 12% products with a suitable pH, and anything above this is not recommended for daily use.

Make Up Artist’s Choice 40% Lactic Acid Peel * – A strong peel produced by the highly-regarded MUAC company. Once weekly is what they recommend, and customers love its effects.


Stratia Soft Touch AHA – This product contains 10% mandelic acid, which means it is a good choice for very sensitive skin.

Make Up Artist’s Choice 25% Mandelic Acid Peel * – Despite being a mild acid, this is a high concentration product. Use with care – About once or twice a week at just 5 minutes per session is adequate.


I personally recommend using blends for regular use. Even though my skin is not blemished, I’ve still seen excellent changes from BHA such as the Obagi Blue Peel Radiance (although this is 20% salicylic acid). Blends containing both AHA and BHA can conveniently give you the positive effects of both types of acid.

Make Up Artist’s Choice Alpha Hydroxy Beta Hydroxy Cleanser – This product contains glycolic acid at 8% and salicylic acid at 3%. A great combination at great strengths. I recommend this product.

Nip+Fab Glycolic Fix Night Pads Extreme – I use these pads every night with a noticeable improvement in my skin. I can’t be certain if this is mostly because of the glycolic and lactic acid component, or because of the salicylic acid (a BHA) which works especially well on me despite having no acne – but either way I like this product and its effects. The pads are also super convenient to use.

The product contains 5% glycolic acid, 1% salicylic acid, and an undisclosed concentration of lactic acid (though we can assume it is below 5%). Based on studies where low acid concentrations were used[3], this should work on the epidermal layer of skin but have no effect on the dermal layer.

Because you can’t use highly concentrated acids daily, one idea would be to use a higher concentration occasionally for the deeper effects on the dermis, and use milder products such as this one daily. You would skip use for 24 hours before and after the stronger acid product to avoid overexfoliation. You could also opt to use the MUAC Alpha Hydroxy Beta Hydroxy Cleanser daily instead.

Transparency Notice: Some of the above links are affiliate links, meaning this website receives a commission when you purchase the products. However, these are legitimate recommendations sourced from skincare communities, and not all of the products use affiliate links.

* With these stronger products, be sure to wash off the solution after use and follow it up with an alkaline product to neutralize any remnants of acid.



Add a Comment

Your email address will not be published. Required fields are marked *