Each cuticle cell contains a thin proteinaceous membrane, the epicuticle, covered with a lipid layer that includes the 18-methyl eicosanoic acid (18-MEA) and free lipids. A thinner cuticle layer makes African hair more prone to breakage. The cuticle is generally formed by 6–8 scales thick for Asians, slightly less in Caucasians and even less in African hair.

The shape and orientation of the cuticle cells are responsible for the differential friction effect in hair. The cuticle is a chemically resistant region and consists of flap overlapping scales (keratinocytes) like shingles on the roof. The medulla may be involved in the splitting of hairs since it provides an area of weakness as a pathway for the propagation of cracks along the axis of the fiber.

There is more medulla in the coarser hair of Asians than Caucasians. The medulla is present in corser hair like grey hair, thick hair and beard hair, and it is absent in fine hair of children. The hair shaft of mammals is divided into three main regions: Cuticle, cortex and medulla. It is a complex structure of several morphological components that act as a unit. Hair is an integrated system with a peculiar chemical and physical behavior. Also, it is important to distinguish hair shed due to telogen effluvium from hair shed due to hair shaft breakage, which is not always clear from the patient point of view. Although scientific data is lacking to prove whether Hispanic hair is really as sensitive, it is common to see Hispanic women with chemically straightened hair, suffering from hair breakage and asking for the dermatologist help and advice to overcome the problem. Hispanic patients also have curly or very curly hair that may clinically behave as sensitive as African hair when exposed to hair care procedures. According to McMichael hair fragility leading to breakage can occur due to genetic predisposition, weathering from various hair care practices. Cosmetic hair care procedures are mostly used by African-descendent women, whose hair fragility has been related to be worsen by hair care practices. Knowing their mode of action, safetiness and ingredients will enable the physician to better assess different problems secondary to cosmetic treatments. The aim of this chapter is to allow a better understanding of the hair shaft structure and behavior, as well as information about the hair cosmetics. Although hair cosmetics are widely available, the medical literature is rather scarce, and specialized literature is not readily accessible. Knowledge of hair cosmetics and esthetic procedures as well as of the hair shaft structure and physical behavior is indeed relevant in today's medical practice. Although dermatologists are experts in managing scalp and hair diseases, the esthetic of some cosmetic therapies still remain elusive.

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