Hair: structure and growth

In short: Hair consists mainly of the protein keratin and grows in a cyclical process that spans years. A person normally loses 50 to 100 hairs per day, which is part of the natural growth cycle.

In more detail: Each hair goes through its own growth phases independently of the others, meaning different hair states exist simultaneously on the head.

In detail

• Growth phase (anagen): In this longest phase, which can last two to seven years, the hair actively grows about one centimetre per month.
• Transition phase (catagen): In this short phase of about two to three weeks, the hair root stops growing and prepares for the resting phase.
• Resting phase (telogen): During this roughly three-month phase, the hair remains inactive before eventually falling out and a new hair grows in.
• Hair follicle: The hair root in the skin contains stem cells responsible for the continuous regrowth of hair.
• Hair colour: Pigment cells in the hair root produce melanin, whose amount and type determine hair colour; melanin production often decreases with increasing age.
• Influencing factors: Genetics, hormones, diet, and stress significantly influence both growth speed and hair density.
• Hair loss: Excessive hair loss beyond the normal range can have hormonal, genetic, or health-related causes and should be checked by a doctor (haut-aufbau-und-funktionen, hormone-und-stoffwechsel).