Hydroxy acids: alpha hydroxy acids (AHAs), beta hydroxy acids (BHAs) and polyhydroxy acids (PHAs)

The depigmenting ingredients that best combat photoaging.

Ideal for: acne, oily skin, pimples, wrinkles, blemishes, rosacea and redness.

Objectives : luminosity, hydration, soften wrinkles and regulate sebum.



1. What are alpha hydroxy acids (AHAs), beta hydroxy acids (BHAs) and polyhydroxy acids (PHAs)?

AHAs are a group of natural acids that come from foods and are hydrophilic, that is, they are soluble in water. For example, citric acid comes from lemon or orange, malic acid from apples or tartaric acid from grapes. And the best known is glycolic, which comes from sugar cane .

Beta hydroxy acids (BHAs) and polyhydroxy acids (PHAs) are acidic derivatives. Salicylic acid (BHA), which comes from white willow, is fat-soluble—it is not soluble in water—and penetrates the skin better compared to AHAs or PHAs. And PHAs are next-generation acids, ideal for use on delicate, sensitive or rosacea skin. One of the most used is gluconolactone, which is obtained from the oxidation of glucose in corn.

2. What kind of ingredients are they?

They are used as active ingredients at variable concentrations and pH depending on the result sought. They are multifunctional ingredients, but they stand out above all for their exfoliating, moisturizing, anti-aging and antioxidant capacity. And they are found in many types of cosmetics, from cleansers, toners, creams, serums, masks, etc.

3. How do I identify them in the list of ingredients (INCI)?

Alphahydroxy acids (AHAs):

  • Glycolic acid (from sugar cane)
  • Citric acid (from lemon or orange)
  • Malic acid (from apple)
  • Mandelic acid (from bitter almonds)
  • Lactic acid (from milk)
  • Tartaric acid (from grapes)
  • Beta hydroxy acids (BHAs):

  • salicylic acid
  • Polyhydroxy acids (PHAs):

  • Gluconolactone
  • Lactobionic acid
  • Maltobionic acid

  • 4. What properties do AHAs, BHAs and PHAs have?

    The properties will depend on the type of hydroxy acid used, its pH and concentration.

    For example:

    • Glycolic acid (AHA) at a pH 4 and a concentration of 3% has a moisturizing function and increases the volume of the epidermis. And at a pH lower than 4 and a concentration higher than 5% it will have an exfoliating action, improving the appearance of skin with acne, wrinkles and blemishes.
    • Citric, malic and tartaric acids stand out above all for their antioxidant properties, they combat damage caused by excess free radicals, which improves skin tone, giving it extra luminosity.
    • Glycolic, lactic and citric acid also have a sebum-regulating function.
    • Salicylic acid (BHA) can only be used at a maximum concentration of 2% and has a keratolytic action, peeling off the upper layer of the stratum corneum and regulating sebum. Which means that it is very effective in reducing blackheads, comedones and even milliums.
    • PHAs such as lactobionic and maltobionic acids and gluconolactone are ideal for gently and delicately removing dead cells from the most delicate skin, in addition to hydrating, smoothing and providing luminosity.

    5. For what type of skin do we recommend these ingredients?

    • Sensitive, dry, rosacea or redness skin: PHAs. In particular, gluconolactone is ideal for reinforcing the skin barrier and hydrating the skin.
    • AHAs also do very well for dry skin. If it is well tolerated, glycolic acid, and if the skin is sensitive, malic acid is better.
    • Oily skin with pimples, blackheads or acne-prone skin: BHAs such as salicylic acid or glycolic and lactic acids that improve the texture of the skin, leaving it smoother and softer.
    • Wrinkles, lack of luminosity and/or photoaging: both AHAs and PHAs.
    • Stains: glycolic and lactic acids.


    • Do not use in children.
    • Do not use salicylic acid if you are allergic to acetylsalicylic acid.
    • Pregnancy: as a precaution, avoid exfoliants with very high concentrations, for example 30%, of glycolic or lactic acids. If, in addition to being pregnant, you have sensitive skin, you can use alternatives such as PHAs or much lower concentrations of AHAs (between 5% and 10%). In the case of salicylic acid, its use is suitable as long as it is not applied to more than 20% of the skin surface.


    6. Recommendations

    - If you have very sensitive, delicate skin or with some pathology and you are looking for an exfoliating action and to reduce wrinkles or spots, we recommend using PHAs. You can also use a cosmetic with glycolic acid at a maximum concentration of 10% because if it is higher it could be irritating. Or instead of glycolic, use lactic, citrus, malic or mandelic, which are softer and more effective. You can use the latter in a concentration between 5-10%.

    - If you have oily, acne-prone skin, an ideal combination to combat comedones and pimples is to use a serum, roll-on or cream that contains salicylic acid, tea tree and zinc PCA.


    7. Frequently asked questions about AHAs, BHAs and PHAs

    Can I use hydroxy acids during the day?

    Be especially careful with AHAs with exfoliating action (more than 5% concentration and pH less than 4) in this case, it is better to use them at night, especially if your skin is delicate, sensitive or very fine. Because the use of AHAs with exfoliating action leaves the skin more exposed, thinner and more sensitive to contact with solar radiation.

    In concentrations greater than 10%, always use them at night. And if you apply a cream with glycolic acid with a moisturizing function, that is, at a low concentration (below 5% and a pH greater than 4%) you can use it without problem during the day always followed by the application of SPF 30 sunscreen or 50.

    With PHAs and BHAs you have no problem. If you use them during the day, finish your routine with sunscreen.

    Can I use them in summer?

    Yes, but keep in mind that if the product is an exfoliant, your skin will be more unprotected and you can burn much more easily with sun exposure. It is best to stop treatment during this time and resume it in the fall.

    Can I use them with Vitamin C or niacinamide?

    Better if they are formulated in the same product. And separately, vitamin C during the day and hydroxy acids at night are better.

    Can I combine them with retinol or derivatives in the same routine?

    If they come in the same formula, yes, but if not, it is better to avoid it because it could be irritating.

    How can I start using hydroxy acids in my routine and do it properly without irritating my skin?

    Start with low concentrations:

    • AHAs between 5 and 10% on alternate days and only at night. Then, as your skin builds tolerance, you can use them daily, in the morning or at night.
    • Salicylic acid: first formulas with a concentration of 1%, then you can try 2%.
    • PHAs are suitable for the most delicate skin, so you won't have a problem with the concentrations.

    If I have very sensitive skin, which hydroxy acid is best for me?

    • PHAs: lactobionic acid, maltobionic acid and gluconolactone.
    • Of the AHAs, mandelic acid, to exfoliate at a concentration between 5 and 10%, and to hydrate at below 5%.
    • Avoid glycolic and lactic acids because, being smaller in size compared to other AHAs, they penetrate the skin more easily.

    If I have very oily, acne-prone skin, which one is ideal?

    • Salicylic acid (BHA) at a 1% concentration in sensitive skin or as long as tolerance is not generated, then you can go to 2%. Keep in mind that during the first applications it is common for you to feel a slight itch.
    • Of the AHAs, glycolic and lactic acids at a concentration of 8-10%.
    • Gluconolactone (PHA) is ideal for pimples or acne-prone skin.

    What if I have stains?

    • Of the AHAs, glycolic and lactic are the ones that have the most evidence in terms of improving spots. Keep in mind that there are many types of spots and that is why we recommend that you go to the dermatologist to diagnose the type of spot and guide the most appropriate global treatment for your case.

    Is it normal for glycolic acid to sting?

    In the first applications it is normal that you feel a slight sting. However, if you have been using it for several days and it irritates your skin, you should stop using it. The ideal, at the beginning of a treatment with AHAs, is to do it every other day and when the skin has created tolerance to this active ingredient, include it every day.

    Bibliography and references

    - Cosmetics applied to Aesthetics and Wellbeing, Aesthetics & Wellness.

    - Beauty with Science, Raquel Marcos Esteban.

    - The definitive guide to skin care, Gema Herrerías.

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