Retinol and skin ageing.

Retinol belongs to the family of retinoids, which are derivatives of vitamin A, such as retinoic acid and retinal. The retinol molecule was first isolated in 1931 by 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. The effectiveness of this organic compound on signs of ageing was demonstrated in the 1980s by American dermatologist Albert KLIGMAN. However, tretinoin is one of the substances banned in cosmetic products according to the European Regulation due to its irritating potential. This active ingredient is only available on prescription to treat severe acne. Studies have shown better skin tolerance for retinol, compared to tretinoin. The European Cosmetic Regulation thus authorises it at a level of 0.3% in a non-rinse product. Applied to the skin, retinol is oxidised into retinal and then metabolised into retinoic acid, its active form capable of effectively combating photo-ageing of the skin and thus smoothing the skin texture.

Retinol operates on several levels to prevent wrinkles or reduce those already present on the skin's surface. Many of its tissue effects are mediated by its interaction with cellular receptors, such as the cellular retinoic acid-binding protein (CRABP) of types I and II and the cellular retinol-binding protein. Retinol and retinoids in general will act on several levels.

• Increasing the thickness of the epidermis.

  With age, the epidermis thins and both cellular renewal and keratinocyte proliferation slow down. This loss of skin tissue promotes the appearance of wrinkles on the skin's surface. Retinol acts by stimulating the proliferation of keratinocytes.

• Limiting the degradation of collagen and elastin.

  These two proteins are key components of the connective tissue that makes up the dermis. They strengthen the skin and increase its elasticity and firmness. Unfortunately, over time, they are degraded by enzymes known asmatrix metalloproteinases (MMP), and more specifically collagenase and elastase. Topical application of retinol inhibits the activity of these enzymes, preventing them from causing harm. Moreover, it stimulates the synthesis of collagen type 1 in the dermis.

• Blocking the damage caused by free radicals.

  Free radicals are highly reactive, unstable molecules that degrade healthy cells and proteins in the body, accelerating its ageing process. They are generated by a variety of factors, the most common being pollution, UV rays, and cigarette smoke. Retinol neutralises these molecules, thereby blocking their harmful effects on the skin.

• Combatting pigmentation spots.

  The appearance of brown spots is linked to the ageing of the skin and/or exposure to external aggressions such as pollution and UV rays. To recall, hyperpigmentation is defined as a disruption in the pigmentation process : the melanin, pigment responsible for the natural colouring of the skin, is overproduced in certain areas which leads to the appearance of brown, red or pink spots that can sometimes be unsightly. Retinol regulates melanocytes and reduces the intensity of pigmented spots on the skin surface.