Module 4: Skin Physiology - Skin And Light

SKIN AND LIGHT:

Radiation striking the surface of the skin can be affected in several ways.

The longer wavelengths of light (UVA especially) penetrate the skin easily reaching the dermis where damage to fibroblasts, elastin and collagen results in the characteristic pattern of accelerated ageing.

At the surface of the skin, light can either be reflected or scattered on impact and thus does no harm.

Once light penetrates the skin a variety of chromophores absorb the radiation depending on the absorption spectrum of the chromophores.

Melanin is the most important of these chromophores. Melanocytes (A) synthesise a variety of melanins (red/yellow pheomelanins; brown/black eumelanins) dependent on the skin colour of the individual.

These are packaged into colour specific melanosomes and transported to keratinocytes where they are distributed over the nucleus of the epidermal cell absorbing the harmful radiation and reducing damage to the DNA.

Although the pigmentary system is essentially for protection against radiation, an understanding of the basic science of pigmentation is essential for anyone managing skin disease, as abnormalities of pigmentation are common sequelae of most skin diseases. This will be elaborated in the next frame.