The skin passes through two major stages in the life of an individual. From birth up to the age of 20 the skin matures. After 20 the skin embarks on a long period of ageing.
At birth, the skin of the newborn, though it seems like an adult one, does have differences. The horny layer is thin, the sebaceous gland secretions cease after the first six months of life, whereas they were very active during intra-uterine life. Because there is no lipidic film, the skin is very suseptible to dehydration. At puberty, the sebaceous glands regain activity triggered by the production of the sex hormones.
From the age of twenty, the skin begins to be subject to the consequences of chronological ageing, causing its appearance to slowly and imperceptibly change.

Ageing over time is the result of a slow, gradual, genetically programmed process, and the aggressions, our skin is subjet to, daily.
The first signs of ageing are seen in the skin of the face. All those funny faces, smiles, twitchings, screwing up the eyes, pursing of the lips finally leave their mark on the skin. These are the origin of the tiny expression lines causes by tension in the facial muscles which draw on the deepest parts of the dermis and over time form deep wrinkles.
The first areas affected are the eye corners where "crows' feet" develop. They start at the eye external angle, as fine cracks then spread out in a fan, deepening to form a network of wrinkles. This process evolves over years before becoming visible. A speeded-up simulation shows this phenomenon clearly. crow feet formation: low bandwidth crow feet formation: high bandwidth
The wrinkles spread little by little over the whole face (the forehead, lips, from the base of the nose to the corners of the lips), the neck, then to all the other parts of the body.
The loss of elasticity of the dermis is not only seen in the appearance of wrinkles. Looseness of the skin is a phenomenon which is also visible on the arms, where the skin frequently