karvatuppeita

Karvatuppeita are microscopic structures in the skin from which hair grows. In humans they reside mainly in the dermis, with some extending into the underlying subcutaneous tissue. Each follicle anchors a hair shaft and includes several components: the hair bulb at the base, the dermal papilla containing blood vessels and signaling cells, and the hair matrix that produces the cells forming the hair. Surrounding the follicle are the inner and outer root sheaths, and the follicle is connected to a sebaceous gland that secretes sebum into the hair canal. The arrector pili muscle, attached to the follicle, can raise the hair when stimulated.

Hair growth follows a cyclical process consisting of anagen (growth phase), catagen (transitional phase), and telogen (resting phase). The duration of the cycle varies by body region, age, and hormonal status. Follicles can be categorized by the type of hair they produce: vellus hairs (fine, light) and terminal hairs (thicker, pigmented). The distribution and activity of follicles influence hair density and pattern on the body.

Developmentally, hair follicles form from epidermal invaginations during embryogenesis. Follicle health and growth can be affected by hormonal changes, injury, infection, and autoimmune or inflammatory conditions. Common disorders include hair loss (alopecia), folliculitis (inflammation of the follicle), and hirsutism in cases of excess hair growth.