- Written by Nadia O'Carroll
Within a single animal there can be various types of keratin. If we look at humans we can identify keratin in our nails, the outer layer or epidermis of our skin and our hair.
On average we have up to 140000 hairs on our heads. The hair grows from a hair follicle at the base of the hair shaft. Under the microscope, an individual hair appears to be covered with overlapping scales like plant pots stacked inside one another, and this layer or cuticle encloses and protects the hair shaft. The cuticle is composed of keratin, which has a structure similar to rods bundled together into cables, this gives hair great tensile strength, and in theory a head of hair could suspend thousands of kilograms. Between 65 to 95% of hair is composed of keratin. Chemically hair is 50.65% carbon, 20.85% oxygen, 17.14% nitrogen, 6.36 % hydrogen and 5.0% sulphur.
Keratin is a colourless protein, it reflects light and gives a gloss to the hair, but the colour of hair is produced by cells called melanocytes, which produce pigment granules. All natural hair colour from light blond to blue black, has the same pigment, it is the density and location of the pigment on the hair which determines colour. Redheads have an additional iron red pigment. When the melanocytes stop producing pigment, hair emerges as white/grey.
If hair is in bad condition it can appear dull and tangled because the edge of the keratin cells become raised, moisture is lost, and the keratin becomes brittle and doesn’t reflect so much light. Hair conditioners work by lubricating the hair, forming a protective film, increasing light reflection and preventing the accumulation of static electricity which makes individual hairs fly apart.
The way keratin molecules are joined effect the shape of hair shaft. When the keratin in a hair is joined more strongly on one side than another, the asymmetry causes the hair to become bent and curly. It is possible to create artificial curls by using heat to disrupt the structural bonds of keratin while the hair is shaped over a brush or curler, but when the hair becomes moist it returns to its original shape. To slow this process hairspray, gel or mousse may be applied and this coats the hair with a resin, which hardens and forms a rigid structure. A longer lasting shape is achieved artificially by applying chemicals, which disrupt the keratin structure, and then after shaping, applying another chemical which allow the keratin bonds to reform.
Keratin is also found in the outer layer of our skin. The cells in our skin contain a structural matrix of keratin and this makes the surface of our skin a tough and waterproof barrier. The amount of keratin in the outer skin cells increases in a process called keratinisation and this eventually causes the cells to die and then to be shed. When an area on the skin surface is constantly pressured more keratin is produced and a callus is formed.
Some infectious fungus such as ringworm and athlete’s foot feed on keratin.
Most of the keratin we interact with – hair, skin and nails are actually dead cells with new living cells pushing up from underneath. The dead cells form a protective layer over the living cells, so generally the thicker the layer of keratin is, the healthier and more protected the living cells.