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Hydroxy acids have many benefits including exfoliation, retexturizing, firming, and brightening, just to name a few. There are three groups of hydroxy acids, Alpha hydroxy acids (AHAs), Beta hydroxy acids (BHAs), polyhydroxy acids (PHAs). Different groups of hydroxy acids work on different layers of the skin thus providing various benefits. Choosing the “right” hydroxy acid depends on your skin type and the skin concern you want to target. Here is a quick guide of hydroxy acids to help you choose the right one.

Alpha Hydroxy Acids (AHA’s)

AHAs work on both the surface of the skin and the deep layer of the skin. On the outer surface, AHAs have an exfoliative effect, helping to shed off the dead skin cells to reveal a brighter, glowing complexion beneath. This also evens skin tone and texture. On the deeper layer AHA’s stimulate collage production which help reduce the appearance of fine lines.

Here are some common AHAs:

Glycolic Acid comes from sugarcane but can also be made in labs. It is considered to be the best AHA. Since it the smallest of the hydroxy acids it has the ability to penetrate through the superficial outer layer of the skin to reach the deeper layers. In doing so it provides exfoliation of the uppermost layers of built-up skin to reveal the better-looking skin hiding beneath. It also helps to hydrate skin by helping the skin retain its natural moisture. Lastly, glycolic acid also enhances skin’s firmness and resilience.

Lactic Acid can be derived from milk, but the synthetic form is used most often in skincare products. It does everything glycolic acid does, but slower because it’s a bit larger. Larger molecules absorb into skin slower thus it has a reduced ability to penetrate skin’s outermost layer when compared to glycolic acid. Lactic acid, just as glycolic acid, has the ability to hydrate skin and acts to exfoliate the skin.

Citric acid comes from various citrus fruits but also can be made synthetically. It can exfoliate skin and also works as an antioxidant. However, it can be irritating to the skin due to its low pH of 2.2. Thus, citric acid is used with other AHA’s as a pH adjuster.

Malic Acid can be derived from apples or produced synthetically. It is larger than glycolic and lactic acids, so its slower acting and provides exfoliation mostly to the outer skin layers. Malic acid also provides antioxidant benefits. It’s typically not used alone but used with the smaller glycolic acid and lactic acid to provide multi-level exfoliation.

Tartaric Acid occurs naturally in grapes but is also made synthetically. It is nearly twice as large as glycolic acid. Although tartaric acid can exfoliate skin it is best in helping to maintain the pH range that other AHAs need to work. It also helps provide more targeted exfoliation, as each size of AHA has its layer-by-layer benefits.

Mandelic Acid isn’t as widely used as other AHAs. It is the largest of the AHA, which means it is the slowest to penetrate into skin. Thus, it acts mostly on the superficial layers of the skin and is less irritating making it the better choice for sensitive skin. Mandelic acid can also prompt the skin to make more oil which can be helpful for those with dry skin.

Beta Hydroxy Acids (BHA’s)

Whilst AHAs are water soluble, BHAs are oil soluble, making them ideal for those with oily skin. BHAs can get below the oil that’s clogging the skin and can penetrate through to the pores to exfoliate inside the pores. They also have antibacterial and anti-inflammatory properties. BHAs are idea for people with acne, blackhead and whiteheads as they help to unclog pores, kill bacteria and reduce inflammation.

Salicylic acid is the most common and widely used BHA. Salicylic acid’s primarily benefit is as an exfoliant. It helps to shed away dead skin on the surface of the skin. It also has the ability to penetrate into the pore lining and exfoliate inside the pore as well. Thus, it is very effective in reducing breakouts, including blackheads and whiteheads. Salicylic acid also has soothing properties helping to calm aggravated and irritated skin. In addition, it can help minimize the appearance of an uneven skin tone and has hydrating abilities resulting in smoother skin. For these reasons salicylic acid is used as the active ingredient in many acne fighting skin products.

Poly-hydroxy Acid (PHA’s)

PHAs are larger in their molecular structure. They are too large to penetrate the skin, so they mostly work on the surface of the skin. They work in the same way as AHAs do to break down the 'glue' that binds dull, dead cells to the surface of the skin. Thus, they exfoliate the outer surface of the skin without disturbing the delicate deeper layers of the skin. Because PHAs provide exfoliation and skin renewal with minimal irritation, they are ideal for people with sensitive skin and those who find AHAs and BHAs too strong.

PHA’s Gluconolactone and lactobionic acid are similar to AHAs in their chemical structure and in their function. Thus, they provide the same benefits of exfoliation as well as improve skin texture and tone, provide hydration, and offer some antioxidant benefits. They also function as antioxidants. The difference is that gluconolactone and lactobionic acid have larger molecular structures, which limits their ability to penetrate the skin. Because of their decreased penetration they cause less side-effects without decreasing their effectiveness. Thus, they are just as effective as AHAs, but less sensitizing. This makes gluconolactone and lactobionic acid a good choice for those with sensitive skin or those who have never used hydroxy acids before.

When choosing between AHAs, BHAs, and PHAs it comes down to the way in which you want the products to work. If your goal is to exfoliate just the top layer of your skin, you should be using an AHA. If your issues are deeper, like cystic acne or just bad acne, you'll want to use either BHA or an AHA/BHA combination. For dry skin, however, you should focus on an AHA or AHA/BHA combo. And if you have sensitive skin, try using PHA’s which are much gentler.

Below are some skin care products which contain AHA’s, BHA’s, and/or PHA’s. Be sure to read all the ingredients to choose the right one for you.

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