ABSTRACT
Hair plays an important role in our well-being and can be a signal of sexual attraction, health and status. If we are happy with how it looks, i.e., having a good hair day, studies have shown our confidence increases. However, the opposite is true if scalp hair is thinning, or has severe damage such as broken or fractured ends. In these cases hair quality can significantly impact self-esteem and well-being. This chapter describes the basics of hair structure and how from a medical history it is possible to determine possible sources of damage, what to look for during examination, and finally what products to recommend. Hair is a complex structure that is made up of proteins, lipids,
melanin, and metal ions. There are three main structural components: the cortex, cuticle, and medulla.1 The cortex makes up the bulk of hair and consists of crystalline a-helical proteins surrounded by matrix proteins arranged in rope-like filaments. The cortex iswhat gives hair its strength, andwhendamagedwill lead to easy breakage. Surrounding the cortex are six to eight layers of cuticle cells which overlay each like shingles on a roof, giving hair its protection from external insults. The cuticle is the strongest part of hair, and if one cuticle cell is broken off, for example during combing, there are others underneath to take its place. Themedulla is at the center of the fiber and varies in distribution and amount. It has a low level of keratins but is high in lipid content (Figure 2.1). Proteins contribute to more than 85% of human hair total
structure, and a significant proportion of these proteins are keratins. The definition of a keratin is a protein containing high levels of cystine amino acid which cross-link different protein chains together via a disulfide bond (-S-S-), giving them high tensile strength. Keratins are the same proteins found in hooves, nails, and turtle shells, making these the toughest natural materials known. Proteins are crucial for hair health, but other structural components
are also important. Lipids, mainly saturated and unsaturated fatty acids, make up 6% to 8% of the total weight of hair and are found at the junction between cuticle cells and also between cortical cells. These lipids are rather like mortar that holds a brick wall of protein together, and if removed by excessive washing or by chemical processes the whole structural integrity of the hair fiber can be compromised. One important example is the f-layer, which is a chemically bound lipid found on the outside surface of each cuticle cell. Its presence makes the outside surface of hair hydrophobic (water drops will bead on hair) and gives hair its soft feel. Exposure to oxidation, either by ultraviolet (UV) light or certain colorants and bleaches, can remove this lipid, making hair lose its hydrophobicity and as described below, making hair more susceptible to tangles and breakage.2
