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Acids have become the protagonists in our cosmetics for one reason: their deep penetration into the skin. This guide brings together the most frequently used acids in cosmetics.

Glycolic acid

It is an acid of the AHA (alpha hydroxy acid) family. It is one of the best known and most widely used in cosmetics. It has exfoliating and moisturising properties, and also promotes the production of collagen in the skin.

Indications: for normal to dry skin, with blemishes or marks, dull. Combination or oily skin can also use it and it can help with acne.

Usage tips: it is photosensitising (potentiates sun damage to the skin). As with all exfoliating products, it should be used with sunscreen (minimum SPF30). It is a “potent” acid and can irritate the skin. It is best to start with low concentrations and gradually add it to your routine.

Contraindications: It should not be used in combination with other exfoliants (retinol, ascorbic acid…), as it may be too much for the skin. Sensitive skin should be used with caution. In the case of formulations that include several acids, there is no problem if we follow the manufacturer’s instructions.

Salicylic acid

Salicylic acid is a lipid-soluble BHA (beta hydroxy acid). It is another of the best known acids, it is also an acid that exfoliates the skin and helps skin renewal. It penetrates deep into the pores of the skin and helps to cleanse them. It is therefore an ideal ingredient if you are looking to cleanse the skin and remove blackheads. It is also antibacterial and anti-inflammatory.

Indications: ideal for oily, combination, acne-prone skin and blackheads.

Tips for use: it can be used day and night as it is not photosensitising, although as it is exfoliating it is advisable to use sun protection during the day.

Contraindications: In very sensitive skins it can irritate, it is better to use formulas with soothing ingredients. Do not use together with retinol.

Hyaluronic acid

This acid has the ability to retain a large amount of water, thus preventing the skin from dehydrating. It provides a juicy and plump appearance to the skin. It is one of the skin care acids that does not exfoliate and is not aggressive to the skin. You can find it in the form of sodium hyaluronate, which penetrates the skin better.

Indications: A must for dry skin, but can be used by all skin types. Helps to retain moisture in the skin.

Suggested use: can be used day and night and in combination with any ingredient.

Contraindications: none, it is suitable for all skin types, even sensitive skin.

Ascorbic acid

Ascorbic acid is the most effective form of vitamin C. It is also the most unstable. It is also the most unstable. Vitamin C is a powerful antioxidant that protects against external factors, such as the sun’s rays. It therefore prevents skin ageing. It also helps the skin recover from external aggressions, brightens and treats blemishes and promotes collagen production.

Indications: For skin with signs of ageing or that wants to prevent them, dull, with blemishes.

Usage tips: It has exfoliating properties, so it is best used at night. Works very well in combination with Vitamin E or alpha lipoic acid products.

Contraindications: It is not recommended to use it together with niacinamide, because it loses effectiveness, although this is a controversial issue and there are different opinions (here one and here another). It is also not recommended for use with retinol.

Lactic acid

Lactic acid is another skin care acid (specifically AHA) with exfoliating capacity. The molecule is larger than glycolic acid, so the exfoliation is more superficial, but also less aggressive. It smoothes skin texture and brightens skin tone, and is more suitable for sensitive skin than glycolic. It also has moisturising properties.

Indications: for dry, sensitive skin, looking to exfoliate and moisturise the skin.

Recommendations for use: like all AHAs, it should be used with sun protection, but as it is less aggressive than glycolic, it is safer to use during the day.

Contraindications: Like other AHAs, it is not recommended for use in the same routine as retinol.

Azelaic acid

Azelaic acid brightens skin tone and diminishes the appearance of imperfections. This ingredient also helps to treat acne and rosacea. It can be used on sensitive skin. It has exfoliating ability, but not as much as other acids.

Indications: for acne-prone, dull or blemished skin.

Recommendations for use: it can be used both day and night, during the day always applying sun protection. If a greater exfoliating efficacy is desired, it can be combined with other products with AHA or BHA.

Contraindications: It is less aggressive than other acids, but should still be used with caution if combined with other exfoliants on sensitive skin.

Mandelic acid

Mandelic acid is another AHA that can be considered “mild”. It gently exfoliates the skin, making it ideal for sensitive skin. People who tolerate acids better may prefer to use glycolic as an exfoliant. In high concentrations, it has antioxidant properties.

Indications: for sensitive skin, with dull skin tone, blemishes or uneven texture.

Suggested use: can be used both day and night, always applying sunscreen during the day. If greater exfoliating efficacy is desired, it can be combined with other products with AHA or BHA.

Contraindications: it is less aggressive than other acids, but should still be used with caution if combined with other exfoliants on sensitive skin.

Alpha lipoic acid

Alpha lipoic acid is not an exfoliant, but a powerful antioxidant. It improves the appearance of the skin, improves skin texture and evens skin tone. Alpha lipoic acid is both water and oil soluble, so it is easily absorbed into the skin. It helps fight free radicals and treats skin ageing.

Indications: for dull skin or skin showing signs of ageing.

Suggested use: sun-sensitive ingredient, unless otherwise stated by the manufacturer, it is best used only at night. Enhances the effects of ascorbic acid when used together.

Contraindications: high concentrations (more than 5%) may cause skin irritation.

New beauty treatment: hyaluronic acid for hair.