Haare

Haare, the German word for hair, are filamentous keratinous structures that grow from hair follicles in the skin of mammals. In humans, hair serves several functions, including protection from UV radiation, insulation, and sensory input through associated nerve endings; it also contributes to appearance and signaling. The body features two main hair types: vellus hair, which is fine and pale, and terminal hair, which is thicker and darker and appears on the scalp, face, and other areas after puberty.

Anatomy: Each hair consists of a shaft that protrudes from the skin and a root anchored in a follicle. The follicle includes the hair bulb, the dermal papilla, sebaceous glands, and sometimes an arrector pili muscle. The hair shaft is organized into the medulla, cortex, and cuticle, and it is composed mainly of keratin. Melanocytes in the follicle provide pigment, giving hair varying colors.

Growth cycle: Hair grows in cycles. The anagen phase is the period of active growth; catagen is a brief transition; telogen is a resting phase during which shedding may occur. A fourth stage, exogen, refers to shedding of the hair. The duration of these phases varies by body region, age, hormones, and genetics.

Health and variation: Hair color depends on melanin type and amount. Normal variation exists in density and distribution across populations. Common conditions include hair loss (alopecia) and excessive hair growth in certain areas (hirsutism); scalp conditions such as dandruff or fungal infections may affect hair quality.