Over thousands of years of evolution human body hair has become increasingly irrelevant as a barrier against the cold and elements. Despite its relative sparsity it has profound social and psychological importance. The ancient Egyptians wrote about hair restoration lotions and twentieth century men continue to search for the elusive baldness cure.
Broadly speaking there are only two hair disorders: too much, and too little.
In order to understand the common problems which can affect our hair and scalp you need some basic knowledge of the structure of our hair and how it grows.
Each hair shaft is elliptical or circular in cross-section and is composed of three concentric layers. The core, known as the medulla, is little more than an air-filled space running down the centre of each hair. Surrounding this is the cortex, which lakes up most of the bulk of the hair and is composed of a tough fibrous protein called keratin. The cortex is in turn surrounded by an outer layer known as the cuticle. The cuticle consists of six to eight layers of flattened cells which overlap each other in much the same way as roof shingles overlap. The cuticle is extremely hard and forms a protective covering around the hair shaft.
The fine downy hair which covers most of the body is known as vellus hair. Unlike the coarse thicker hairs (known as terminal hairs) that sprout from areas such as the scalp, eyebrows and pubic area, vellus hair is short, virtually colourless and has no medulla. If you look on the inside of your forearms you will see typical fine vellus hair.
The quality of hair is determined by minor variations in the hair shaft. For instance, straight hair is perfectly circular in cross-section whereas wavy or curly hair is more slender and elliptical. Negroid hair is flattened and ribbon-like, giving its characteristic tightly coiled quality. The condition of the cuticle determines how light is reflected from the hair. When the cuticle is badly weathered and individual cells stick out or are lost, or if the cuticle is covered by grease and dust, the hair appears dull and lifeless. If the cells are overlapping and lying flat against each other like a neatly tiled roof, light will be reflected evenly from this smooth surface and the hair will appear glossy and smooth.
