hårfollikelen

A hårfollikelen, often translated as hair follicle, is a vital structure in the skin responsible for generating hair. It is a complex, invaginated sheath that extends from the epidermis down into the dermis. Within this follicle, specialized cells, particularly the hair matrix cells, undergo rapid division and differentiation to form the hair shaft. The hair shaft itself is primarily composed of keratin, a tough, fibrous protein.

The hair follicle cycle is a dynamic process involving three main phases: anagen (growth), catagen (transition), and telogen (resting). During the anagen phase, which can last for several years, the hair grows actively. The catagen phase is a short, transitional period where the follicle shrinks. Finally, the telogen phase is a resting period, after which the old hair is shed, and a new anagen phase begins, initiating the growth of a new hair.

Associated with the hair follicle are several other structures. A sebaceous gland typically opens into the upper part of the follicle, secreting sebum, an oily substance that lubricates the hair and skin. An arrector pili muscle, a small smooth muscle, attaches to the follicle and can contract in response to cold or fear, causing the hair to stand on end, a phenomenon known as goosebumps. The health and function of the hair follicle are crucial for hair growth and overall skin health. Various factors, including genetics, hormones, and environmental influences, can affect the hair follicle's activity and lead to conditions such as hair loss or excessive hair growth.