To understand why dermatitis occurs we must first learn a little about the human skin - how it functions and how it is constructed.
The skin is the body's largest single organ. The average adult has around 21 square feet of skin, with around 300 million skin cells equating to approximately 10% of their body weight. It carries out many purposes, to regulate the body's temperature, ward off infections and sense heat, cold and vibrations. As long as the surface is unbroken by cuts, abrasions or disease, and the natural secretions are not removed or contaminated, the skin is an excellent barrier.
As the body's outer layer, it acts not only as a protective barrier from the external environment, preventing substances and from microbes reaching our internal organs, it also retains vital body fluids.
For simplicity, we can think of the skin as having two layers, the epidermis and the dermis.
The outer layer of the skin is the epidermis, which itself consists of several layers, the outer-most layer being the stratum corneum or horny layer consisting of dead cells.
These are only attached loosely, and are constantly being shed and replaced from the layers below. In addition to these cells growing up from the basal layer, the epidermis contains other specialized cells such as pigment cells.
The dead cells are covered by a film of sebum, an oily substance secreted by the sebaceous glands, which helps to keep the skin supple. It is very important to keep this outer layer intact, for in a healthy state it is strongly resistant to bacteria and external agents.
Below the epidermis lies the dermis, or true skin, which consists of fibrous and other tissues well supplied with blood vessels. In addition to the nerve endings responsible for the sense of touch and pain, the dermis also contains three other important components.
- Hair follicles — A sheath inside which the hair grows
- Sebaceous glands — Produce sebum
- Sweat glands — Produce perspiration
These three are vulnerable parts of the system since they all connect directly with the surface of the skin. To keep skin healthy, these openings should always be kept free from blockage by industrial soilings, such as oil and grease.
When skin is behaving normally, the sebum forms a protective coating on the surface. But in certain cases these openings can provide direct access for damaging substances.