A human head contains about 120,000 strands of hair
Hair covers the head. An individual strand has an average diameter of 1/15th of a millimetre. Head hair and body hair have the same structure and belong to the family of epithelial appendages, like nails (growth from the epidermis).
The main function of hair is to protect the head (and therefore the brain), from physical shock, UV rays, heat and cold, etc.
Hair is composed of keratin, which is a very strong fibrous protein; a single hair can withstand a weight of 100g and a lock of 100 hairs can support a weight of 10kg.
A human head contains about 120,000 strands of hair (between 100,000 and 150,000), with an average density of 250 to 350 hairs per cm². However, this figure can vary according to several factors, such as gender, age, pigmentation, physical conditions, eating habits, or even climate or ethnicity.
There is also a rule that the lighter the hair, the thinner the hairs will be, but more abundant. Conversely, the darker the hair, the thicker the hairs will be, but fewer.
Over a lifetime, a hair will renew itself 20 to 25 times. Each renewed hair will have a lifespan of three to five years in men and four to seven years in women, and grow an average of one centimetre per month.
Of course, every day, some hair will fall out, as it undergoes the law of seasonality. In fact, a person loses 45 to 60 hairs per day in spring and summer, and up to 100 hairs per day in autumn.
Hair does not grow continuously but in a cyclical and periodic rhythm, which can vary depending on the individual, the person’s age and the season. This is the hair cycle.