After what period of time can we see the effects of retinol on the skin?

The retinol is one of the three synthetic isomers of vitamin A. Being fat-soluble, it belongs to the class of chemical compounds derived from vitamin A, commonly referred to as retinoids. Retinoic acid is the purest and most active form of vitamin A but also the most unstable, which is why it is only available on prescription.

In cosmetics, we utilise retinol, retinaldehyde, microencapsulated retinol or its esterified forms such as retinyl palmitate (INCI name: Retinyl Palmitate), retinyl acetate (INCI name: Retinyl Acetate), retinyl linoleate (INCI name: Retinyl Linoleate) or retinyl propionate (INCI name: Retinyl Propionate) which are gentler as they present a lower risk of skin irritation.

In the body, vitamin A performs numerous biological functions: it is involved in embryonic development, the maintenance of the immune system, vision, growth and cell differentiation, tissue renewal... In the skin, it regulates many processes and provides various benefits such as:

• Antioxidant: Retinol has antioxidant activity, meaning it protects the skin from ageing by preventing the action of free radicals (oxidative stress), which are compounds that damage skin cells and are responsible for the emergence of the first signs of ageing.

• Anti-wrinkle and firming: retinol aids in increasing and accelerating cellular renewal, thus having a similar effect to a exfoliating action, as it removes dead cells and generates new ones. It also holds this activity in its ability to restart the dermal synthesis of three matrix molecules, which contribute to the maintenance of the skin structure, by stimulating the fibroblasts for prolonged use: elastin, collagen, and glycosaminoglycans (hyaluronic acid) known for retaining a significant amount of water. Its action on collagen is twofold: in addition to stimulating its production, retinol also reduces the amount of collagen degraded by sun exposure. It thus helps to correct the damage that occurs during skin ageing: it restores firmness, flexibility and density to the face, and reduces wrinkles.

• Comedolytic : By reversing abnormal desquamation through the enhancement of skin cell regeneration and accelerating the removal of corneocytes, retinol then promotes an inhospitable aerobic environment for the Propionibacterium acnes, the main bacteria involved in acne. Similarly, its "exfoliating" function also helps to clarify the pores, minimise their size due to its cell communication abilities, and cause a regression of lesions. As a result, the skin texture is "smoothed", the pores appear less dilated and imperfections no longer form.

• Depigmenting: Supported by a modest evidence base, retinol also helps to reduce brown spots and thus even out the complexion, particularly by inhibiting the activation of matrix metalloproteinase, oxidative stress, reducing the transfer of melanosomes, and the regeneration of the extracellular matrix. Furthermore, retinol regulates the differentiation of keratinocytes, contributing to the acceleration of desquamation and consequently affecting the amount of melanin in the epidermis. Finally, the thinning of the corneal layer through the use of retinoids can increase permeability and thus the penetration of depigmenting products into the epidermis, increasing their bioavailability, thus promoting depigmentation.