When temperatures plummet and the air becomes drier, the skin is put through its paces. Designed to act as a barrier, it must constantly adapt to changes in its environment. Winter imposes specific challenges: between the cold, wind, decreasing humidity and indoor heating that dries out the air, the skin's balance is compromised. The result: the skin's insensible water loss (IWL) increases, its surface becomes rougher and feelings of discomfort set in. When this dryness becomes very significant, it is referred to as xerosis. This phenomenon is based on several factors that impair the skin's ability to maintain its hydration.
One of the initial consequences of cold on the skin is the reduction in lipid production. To recap, the skin is composed of three layers: the epidermis, the dermis, and the hypodermis. The outermost layer, the epidermis, is itself subdivided into four layers, including the stratum corneum, located on the surface. Between the corneocytes, the cells of the stratum corneum, are lipids, such as ceramides, cholesterol, and free fatty acids, which seal the cells together and prevent the evaporation of water. This evaporation is also limited by the hydrolipidic film, a mixture of sweat and sebum that covers the skin.
Indeed, when temperatures drop, blood vessels tend to contract: this is known as vasoconstriction. To preserve the warmth of vital organs, such as the heart and lungs, the body reduces blood flow to the skin, which slows down the supply of oxygen and essential nutrients for the production of sebum and epidermal lipids. With fewer ceramides to ensure cellular cohesion and a weakened hydrolipidic film, the skin becomes more permeable and water evaporates more easily. This mechanism is amplified by the humidity of the outside air, which significantly decreases in winter. The water contained in the skin then escapes into the surrounding air. The drier the air, the faster this evaporation occurs, thus accelerating skin dehydration. Moreover, the wind, often strong in winter, exacerbates this process by sweeping away the hydrolipidic film.
Finally, beyond these biological phenomena, certain daily habits contribute to worsening winter xerosis. Hot showers and baths, although comforting during this season, tend to dissolve the lipids in the epidermis, further weakening the skin barrier. Similarly, heating systems significantly dry out the surrounding air, intensifying the skin's water loss.
Winter xerosis results from an increased loss of water through the skin, primarily caused by the cold, wind, and a decrease in ambient humidity.