Retinoids and Acne.

Retinoids include vitamin A, its metabolites and derivatives (both natural and synthetic). Retinol, retinoic acid and retinal are the three available forms of vitamin A. These molecules belong to the family of first generation retinoids. Their history can be traced back to ancient Egypt, where beef liver compresses (containing retinol) were used to treat blindness, hence their names which derive from the "retina" of the eye.

It was in 1931 that the retinol molecule was isolated for the first time by the Swiss chemist Paul KARRER, from mackerel liver oil. The first study using tretinoin (or all-trans retinoic acid) to treat acne was published in 1943.

Some retinoids are only available by prescription and belong to the family of drugs. These are the retinoic acids, which come in three forms:

• Tretinoin, usually concentrated at 0.025% to 0.05%, alone or combined with erythromycin (a local antibiotic)

• Isotretinoin, alone or in combination with erythromycin

• Adapalene, alone or in combination with benzoyl peroxide (local antiseptic)

When applied to the skin, these compounds will help remove blackheads and soothe inflammation. They also stimulate skin cell renewal and act directly on blackheads and microcysts. They fight bacteria accumulated in pimples, such as P. Acnes.

They are used in the treatment of mild to severe acne, alone or in combination (with local treatments based on benzoyl peroxide for example).

The use of topical retinoids to treat acne usually lasts three months. Applying retinoids to the skin to treat acne can cause side effects such as irritation, redness and allergies. They can also make the skin dry and more sensitive to sunlight. It is therefore recommended that you always apply a moisturizer and sunscreen during treatment.

Three retinoids are available on the cosmetic market and do not require a prescription. They can limit acne that is just beginning and/or not very intense. They are the following compounds :

• Retinol

The most popular retinoid in skin care, it is considered one of the most effective compounds to fight against the signs of aging and sagging skin. Generally recommended for mature skin, it is also recommended for oily and/or acne-prone skin. Its keratolytic properties allows it to eliminate the dead cells present on the surface of the epidermis. The pores are cleansed, and the skin texture is refined, thus preventing the appearance of blackheads and/or comedones.

• Retinal

Chemically, retinal is an intermediate metabolite between retinol and retinoic acid. In other words, when applied to the skin, retinol is oxidized into retinal and then metabolized into retinoic acid, its active form capable of fighting acne effectively but prohibited in cosmetics because it is too irritating.

• Retinoid esters

These compounds are generally used because of their greater chemical stability compared to retinol or retinal, but also because they are the most gentle retinoids for the skin. The most common are retinyl acetate (INCI: Retinyl acetate), retinyl propionate (INCI: Retinyl propionate), retinyl palmitate (INCI: Retinyl palmitate) and retinyl linoleate (INCI: Retinyl linoleate). They are easily identified with the suffixes "ate". Nevertheless, retinol esters are less effective on acne than retinol or retinal because they have to undergo more transformation in the skin before taking the form of retinoic acid. Esters are relevant if you have sensitive skin but still want to start incorporating retinoids into your beauty routine.