Our skin contains natural ingredients that protect it and keep it hydrated. These substances form the outermost layer of the skin (the stratum corneum). When the functioning of this outer shell is disrupted, our skin loses water. Dry skin is a common problem that is tricky to resolve. But why does our skin become dry?
We wash too often, use highly alkaline soaps and expose ourselves to excessively dry air from heating and cooling devices. Often we lead a lifestyle that does not allow the skin to follow its natural regeneration cycles. We know that hydrated skin is essential for the epidermis, most especially its outer protective layer, to retain its structure and function properly. When its barrier function is altered, the skin loses water and shrivels like a leaf, which is when we notice discomfort and even itchiness. In short, the skin dries out.
The skin, a tissue in constant motion
Skin tissue is like a fabric that is constantly being woven and unravelled. The outermost layer, the epidermis, whose average thickness is only 0.5 mm, protects the skin from the external aggressions that often remove moisture. Necessary to regenerate the skin periodically are essential living cells in the epidermis called keratinocytes. These cells weave the threads of the stratum corneum.
This is how the process unfolds. The keratinocytes develop and multiply in the deepest layer of the epidermis (the basal layer). They then move up to a more superficial layer, called the stratum spinosum, where they mature and mix with fats packaged in little bags called lamellar granules, containing free fatty acids, ceramides and cholesterol. These granules occupy the space between the keratinocytes and bind them together. Held together in this way, the keratinocytes progress to the outermost layer of the epidermis (the stratum corneum).
Bricks and mortar
The skin that we see is, in fact, the keratinocytes at the end of their trip: when they reach the skin surface they die. Their skeletal remains form the bricks of the protective layer. These dead cells, which play a crucial role in keeping the skin hydrated, are continually shed by the skin.
The whole keratinocyte cycle, from birth to death, is known as the bricks-and-mortar cycle. The dead keratinocytes are the bricks and the lipids (fats) form the mortar. Between them they build the skin’s retaining wall: bricks without cement or cement without bricks alone are not enough.
This skin layer is regenerated every 30 days in young people and every 50 days (or more) in older people. The skin becomes dry when the keratinocytes fail to multiply or mature properly, when they do so too slowly or when the lipids (the mortar) fail to keep the bricks together.
Natural moisturizing factor (NMF)
Before they reach the outer layer, keratinocytes produce a molecule essential for skin hydration, called filaggrin, which binds to the keratin fibres containing keratinocytes and prevents moisture from seeping through the skin. When filaggrin has completed its task, it breaks down into the amino acids that make up its structure.
This degraded filaggrin forms part of natural moisturizing factor (NMF), a group of substances that binds to water molecules to keep the skin hydrated. This “physiological cosmetic” is also composed of lipids (fat) in emulsion, water from sweat, lactic acid, pyrrolidone carboxylic acid (PCA) and urocanic acid.
Water in the skin
The three elements that act as moisture retainers in the epidermis – moistening the skin and preventing the entry of harmful substances – are the dead keratinocytes, the lipids that hold them together and the natural moisturizing factor resulting from degraded filaggrin. When the skin’s barrier function fails, its equilibrium is lost; consequently it fails to retain water and the result is dryness and irritation.
Although some people may suffer from dry skin for genetic reasons or as a result of metabolic imbalances or environmental or chemical aggressions, keeping the skin healthy and hydrated is not difficult if these tips are followed:
- Shower in warm water using soaps or gels with a pH of less than 5.5.
- Gently dry the body and apply a moisturizer all over while the skin is still damp.
Our skin asks for gentleness, moderation and constant care. When it comes to hydration, its delicate balance hangs by a thread.