Hair

Hair is a filamentous biomaterial, largely composed of the protein keratin, which grows from follicles found in the dermis, the second layer of skin. It serves multiple biological purposes, including protection from environmental factors, sensory function, and thermoregulation. Human hair is divided into two structures: the hair follicle, which is the living part embedded within the skin, and the hair shaft, which is the non-living part that we observe extending beyond the skin's surface. The hair growth cycle includes the anagen (growth phase), catagen (transitional phase), and telogen (resting phase), followed by the shedding of the hair shaft.

From a medical standpoint, the condition of a person's hair can be indicative of their overall health and can signal nutritional deficiencies or hormonal imbalances. For instance, thyroid dysfunction or iron deficiency anemia can lead to hair loss or changes in hair texture. Hair analysis can also be useful in diagnosing medical conditions, determining drug use, or identifying genetic disorders. Additionally, abnormal hair growth patterns or loss can be associated with diseases such as alopecia areata or polycystic ovary syndrome (PCOS). Medical interventions for hair-related issues range from topical treatments and medications to surgical options such as hair transplantation.