Fjunhår

Fjunhår, also known as vellus hair, refers to the fine, soft, and usually unpigmented hair that covers most of the body of humans and other mammals. This type of hair is distinct from terminal hair, which is thicker, coarser, and typically pigmented, such as the hair on the scalp, eyebrows, and pubic regions. Vellus hair is characterized by its short length, thin diameter, and lack of a medulla, which is the central core found in terminal hairs.

The development of vellus hair begins in infancy. During puberty, hormonal changes lead to the replacement of much of the vellus hair with terminal hair in many areas of the body, a process that is particularly pronounced in males due to higher levels of androgens. However, vellus hair persists throughout life on a significant portion of the skin's surface. Its primary functions are thought to include thermoregulation by trapping a layer of air close to the skin, sensory perception, and the distribution of sebum, an oily substance produced by sebaceous glands.

While generally present on everyone, the visibility and density of fjunhår can vary considerably among individuals, influenced by genetics, age, and hormonal status. In some cases, medical conditions or treatments can affect vellus hair growth. For instance, conditions like hirsutism involve the excessive growth of terminal hair in a male-like pattern, while hypertrichosis can lead to an unusual increase in vellus hair growth across the body.