Acids in skincare 101

Acids in skincare 101

Some of you may wonder, why would some brands put acids in skincare? Don’t acids burn the face like those accidents you see in the news?

That's because those mentioned in the news often involve the use of extremely strong acids that are too damaging to the skin. But that doesn’t mean not all acids are bad.

There are generally two types of acids, strong and weak acids. Strong acids like sulphuric acid and hydrochloric acid are usually regulated for use in industrial applications, which means you’ll never find them in consumer markets like skincare.

On the other hand, weak acids such as glycolic acid and salicylic acid are beneficial to skin in the right amounts since our skin is slightly acidic. Basically, the skin takes a really long time to shed dead layers of cells at the surface to give space for the new layers of cells beneath. Using such acids speed up this process by gently exfoliating to improve facial complexion and revealing healthy-looking skin. There are many types of weak acids but we will focus only on the weak acids used in skincare here.

In personal care, we categorise these weak acids into three more types based on their chemical structure. These are:

  1. alpha-hydroxy acids
  2. beta-hydroxy acids
  3. poly-hydroxy acids

Alpha-hydroxy acids (AHAs)

Most acids you find in skincare products often belong to this category except salicylic acid which is a beta-hydroxy acid (we'll cover this later). Example of AHAs include glycolic acid, lactic acid as well as other fruit acids such as citric, tartaric and malic acid.

Although they come in slightly different forms, they all generally have one common function — to exfoliate and hydrate the skin. We'll briefly talk about glycolic acid since it is the most studied and assessed by researchers based on effectiveness.

Glycolic acid

Being the smallest in the AHA family in terms of molecular size, glycolic acid is the most potent AHAs found in skincare. This is because the smaller the molecular size, the more likely it can penetrate the skin. Although most sources say that glycolic acid is recommended for dry skin, we strongly believe that glycolic acid is suitable for most skin types including oily skin based on our personal experiences. Because healthy skin needs some form of exfoliating and hydrating elements.

One should only be concerned if they already have extremely irritated skin before trying out glycolic acid, due to it being the most potent AHA.

Beta-hydroxy acids (BHAs)

There's only one that is commonly used in skincare which is salicylic acid. Unlike AHAs, BHAs are oil soluble which means that technically, it can dissolve in the oily sebum in our skin to exfoliate inside the pores. But this also means that it won't dissolve simply into most skincare formulas as they are often water-based, which is why it is added with a penetration enhancer like alcohol or propylene glycol.

Adding these enhancers not only helps the acid to dissolve into the formula but also penetrate and exfoliate deeper into the skin. In some cases however, these may cause irritation for those with very sensitive skin.

Salicylic acid

Found in most skincare targeted towards acne, it is effective against breakouts and blemishes such as acne, blackheads and whiteheads. It also has anti-inflammatory properties to soothe skin irritation which often occurs in acne-prone skin.

Poly-hydroxy acids (PHAs)

These are a group relatively new acids in the market such as gluconolactone and lactobionic acid. They tend to be less irritating and are claimed to be effective against wrinkles and hyperpigmentation. However, there is not much scientific evidence available compared to the others mentioned above. Also, some are patented which means that only a selected number of brands produce it and sell at a higher price point.

Which exfoliating acid is suitable for me?

There are a few things to consider when figuring out which exfoliating acid is suitable for you. One is pH— the lower the pH the more free acid available to be absorbed by the skin. As a rule of thumb, look for formulas that are in the 3.5-4.5 pH range.

Another is the percentage added into these formulas. Generally speaking, the higher the percentage, the more potent the formula. There are some exceptions however. For example, a 5% lactic acid may be more potent than a 1% glycolic acid although glycolic acid is the more potent AHA.

Also, it is possible for 5% glycolic acid to be more potent than its 10% percent counterpart if its pH is considerably lower. 

Therefore, you would need to put such factors (molecular size, concentration and pH) into consideration when judging the potency of the formula.

What you need to know (tl;dr)

AHAs, BHAs and PHAs are commonly used acids in skincare. All of them exfoliate the skin at various degrees. Consider molecular size, concentration and pH.

Glycolic, lactic and salicylic acid are probably the most potent acids in this list. They also have the most scientific evidence available amongst the rest which means that they are most studied and assessed by researchers based on effectiveness and safety.

Other acids are less potent but that also means that they are less likely to cause skin irritation.

Most importantly, what matters is always the percentage/concentration and pH. The higher the percentage AND the lower the pH, the higher the potency and chance of effective results but also higher chance of irritation.