Cutaneous system consists of skin, its glands (sweat/sebaceous glands) and appendages (hair, horn, hooves, nails etc). Main purpose of skin is to protect underlying soft tissues from injuries and harsh environment. Interesting features are:
Spread out flat the skin would cover the area of a single bed.
Most of us have about 110,000 head hairs. Those with lighter hair have a few thousand more, those with darker hair, a few thousand less.
A typical head hair grows about 3 mm each week. After a few years it stops growing and falls out, and its follicle rests. Months later, a new hair grows from the same follicle. This affects different hairs at different times. Otherwise, every few years we would suddenly go bald!