Juuksekasvu

Juuksekasvu, or hair growth, is the process by which hair is produced by hair follicles in humans and other mammals. It occurs in cyclical phases that regulate the length and density of hair. The main phases are anagen (growth), catagen (transition), and telogen (resting); some descriptions also include exogen (shedding). The duration of the anagen phase largely determines how long a hair can grow. On the scalp, the anagen phase typically lasts several years, while on other parts of the body it may last only months, resulting in shorter hair in those regions.

Hair growth depends on the structure of the hair follicle and its surrounding tissues. Each follicle contains a hair bulb and papilla that supply nutrients and signaling molecules to keratinocytes, which form the hair shaft. Melanin-producing cells in the hair bulb give hair its color. Growth rate varies by individual and body region, but scalp hair generally grows about 1 to 1.5 centimeters per month.

Regulation of juuksekasvu is influenced by genetics, hormones (notably androgens), age, nutrition, and overall health. External factors such as stress, illness, medications, and scalp conditions can affect growth and shedding. Common conditions associated with altered hair growth include androgenetic alopecia, alopecia areata, and telogen effluvium, as well as scalp infections or inflammatory diseases.

Maintenance of healthy juuksekasvu involves balanced nutrition, good scalp care, and management of underlying medical conditions. Treatments for unwanted hair loss include topical or oral medications, hair transplantation, and laser therapies; approaches for encouraging healthy growth focus on addressing contributing factors and supporting follicle function. Research continues into the molecular pathways that regulate the hair cycle, including stem cell activity in the follicle bulge.