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Lactic Acid vs Glycolic Acid: The Battle of AHAs in Skincare

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It’s amazing to think that it took so long for people to start adding alpha-hydroxy acids (AHAs) to their skincare routine. These acids have a variety of benefits, including exfoliation, skin brightening properties, increased collagen production, and reduced wrinkles that we simply cannot overlook. That’s why today, AHAs’ popularity has skyrocketed, and they are rarely missing from skincare freaks’ routines. While there are many types of alpha-hydroxy acids with different strengths, above all stand glycolic and lactic acids — two AHAs you most likely heard about. 

Although both are structurally very similar and mostly do the same thing, like breaking down dead cells, lactic acid and glycolic acid work slightly differently. Besides, the exfoliating effect that both AHAs have in common, glycolic and lactic acids have their own properties that react individually with everyone’s unique complexion. So, which one is better? Lactic or glycolic acid? Well, there’s no general answer to this question. The right question should be which one is more suitable for me? Pretty much, it all depends on your skin type and what your expectations are.

So let me tell you how AHAs work, what glycolic and lactic acids have in common, and what makes them different from each other so you can figure out which one is best for you!


What are AHAs?

Have you ever had a chemical peel? It’s like a really intense facial that can leave your skin feeling tighter, smoother, and more youthful. AHAs are chemicals that act as exfoliants, being great peeling agents. They work by reducing the bonds between dead skin cells and those in your skin’s top layer, which makes them easier to shed away. This exfoliating effect may generate a slight burning sensation, so don’t go crazy when you feel your face on fire. According to many studies, AHAs’ effectiveness depends on pH, concentration, and exposure time. I’ll go into that later on.

AHAs are water-soluble acids found in sugarcane (glycolic acid), sour milk (lactic acid), and fruits (citric and malic). AHAs are considered anti-aging powerhouses thanks to their ability to remove old skin cells and encourage new ones to take their place, which helps diminish wrinkles and fine lines. This also helps new collagen fibers form and replace the old ones — you know how important collagen is to keep your skin firm and tightened, right? Besides, AHAs help brightens the skin and reduce dark spots.

Glycolic, citric, malic, tartaric, and lactic acids are AHAs commonly used in skincare, from which glycolic and lactic get the most attention. Here’s what you particularly need to know about these two acids.

Glycolic acid

Out of all AHAs, glycolic acid has the lowest molecular weight, allowing it to penetrate the deepest among others acids. This means glycolic may exfoliate more effectively, but it’s also the riskiest, as it can cause irritations, dryness, and increased UV sensitivity.

Apart from that, when used on a regular basis, glycolic acid can help minimize the appearance of fine lines and wrinkles while smoothing out rough patches on the surface of your skin that may be causing uneven texture. Glycolic acid is also effective in reducing acne, thanks to its antibacterial and anti-inflammatory properties.


Understanding the importance of AHA’s pH and concentrations

Like all AHAs, the effectiveness and safety of glycolic acid mostly depend on pH and concentration. In order to work, AHAs have to pass through the epidermis (outer layer of the skin), and they can only do that when they’re in their free acid form. pH is a measure of a substance’s acidity or alkalinity, and in the case of AHAs, it practically shows what percentage of AHA is in the free form.

When glycolic acid is formulated at lower pH means more of the acid is in the active form. For example, glycolic acid must be at a pH of 1.5 to be in 100% active form, while at a pH of 5, only 6% is free acid.

Basically, the pH dictates the amount of AHA in your product that’ll be absorbed into your skin — where lower pH means better absorption. If a product with 10% glycolic acid would be formulated at a pH of 1.5, your skin will absorb 10% of glycolic acid, while if it would be at a pH of 5, only 0.5% glycolic acid will pass through the epidermis.

That’s the tricky part about glycolic acid. It requires to be formulated at higher pH where the percentage of free acid is lower thus, you need a product with a larger concentration of glycolic acid in order to effectively penetrate the skin. Besides, too much free glycolic acid penetrating your skin at once may be dangerous and can disrupt your skin’s natural pH (which is around 5.6), and damage your protective skin barrier.

According to the FDA, the AHA concentration in a product should be 10% or less at a pH of 3.5 or greater to be considered safe and effective, although it’s common to use higher concentrations (up to 30%) for chemical peels. For glycolic acid, studies found that the optimal pH ranges from 3 to 4.5, where it effectively kills acne bacteria, reduces wrinkles, and fades hyperpigmentation.

If your skin barrier is damaged, you should avoid high concentrations of glycolic acid. You’ll know it’s damaged if your skin is dry, dull, and sensitive. In this case, you should give lactic acid a try. Here’s why.

Lactic acid

Lactic acid is structurally similar to glycolic acid but is gentle and draws moisture to the skin. It acts as a humectant, meaning it attracts water and binds it to the skin. Some studies also point that lactic acid may promote ceramide synthesis within the skin, which helps strengthen the skin barrier and lock moisturizer. There’s not much data about lactic acid’s optimal pH, but it’s believed to be between 3-4, where’s unlikely to cause irritations. That makes it more suitable for sensitive skin types.


Lactic acid vs. glycolic acid

The differences between glycolic acid and lactic acid can get confusing, but here’s what they have in common: they act as peeling agents by removing old skin cells and promoting new collagen fibers. This makes both glycolic and lactic acids capable of reducing aging signs, breakouts, and hyperpigmentation. However, glycolic has higher exfoliating power than lactic acid, plus antibacterial proprieties, thus it’s believed to work better at clearing up breakouts and scarring caused by acne.

Lactic vs Glycolic
Lactic acid vs. glycolic acid

Since it has the smallest molecule size among AHAs, glycolic can penetrate the deepest and is rated as the strongest one. But for some people, especially those with dry or sensitive skin, glycolic acid might feel too harsh and cause irritations.

Lactic acid, on the other hand, mimics the skin’s own natural moisturizing systems, and studies confirmed it to be less irritating than glycolic acid. Lactic acid, which is gentler than glycolic, is considered to be an excellent moisturizer and is more appropriate for people with dry skin. Besides, lactic has a lower pH than glycolic acid, thus it can work effectively at lower concentrations, making it suitable for sensitive skin. 

Which one should I use?

No matter how much we love AHAs, their improper use may damage the skin barrier function, leading to dryness (thanks to the increased transepidermal water loss), irritations, and sensitivity. It’s deadly important to know which acid to use and how to use it. If your skin is oily or you have acne, you should use glycolic acid because it has antibacterial properties and regulates oil production more effectively. Plus, oily skin is less likely to get irritated, but it always helps to do a patch test before. 

On the flip side, it’s best to go with lactic acid if you have dry skin because it’s hydrating and less irritating — that also makes it a better choice for sensitive skin. Besides, sensitive or dry skin might be a sign of a disrupted skin barrier, and lactic acid helps to strengthen it. For wrinkles and dark spots, both AHAs can help you, but if I were you, I’d put my money on glycolic acid if your skin can handle it. 

Can I use them together?

Why would you do it? They’re both peeling agents, and using them together, you only risk over-exfoliating and destroying your skin barrier. You should also not mix any AHA with other exfoliator agents such as retinol because of the same reason. 

How to use AHAs?

How to use your AHA product mostly depend on the product at hand. If it’s a cleanser or toner, it can be used daily. Moisturizers and serums with higher concentrations of AHAs (above 10%) are usually used two or three times weekly. You don’t need to exfoliate too often anyway.

If it’s your first time with AHAs, start with low concentrations until your skin builds tolerance. Increase the concentration slowly and safely. By teaching your skin this way, you may go to even stronger AHA products. In case your skin is super dry or irritated after exfoliating, make sure to apply a moisturizer and stop the AHA for a while. Last but not least, don’t forget your sunscreen. AHAs, especially glycolic acid, increase the skin sensitivity to UV rays, your first enemy. 

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