**4. Chemical composition of hair**

Hair has a complex chemical structure, containing organic substances (glycogen, acidic polysaccharides, lipids and proteins—amino acids). About 90% of the hair structure consists of proteins, out of which keratin (a combination of 18 amino acids) is the essential component, being produced by the skin keratinocytes. The lipids represent 3% of the hair composition and are supplied by the sebaceous glands or produced in the hair bulb from sterols, fatty acids, and ceramides [12, 13].

Hair also contains inorganic substances (carbon 45.2%, oxygen 28%, hydrogen 6.6%, nitrogen 15%, and sulfur 5.2%) and water. Other mineral components of hair consist of iron, copper, calcium, magnesium, zinc, potassium, and lead, all of them of external sources.
