Why do some hair and nails grow faster than others?

Hair and nails are much more than aesthetic attributes: their speed of growth has always been intriguing. Hair grows on average one centimeter per month, and nails about 3 millimeters. But some people, who grow quickly, have to cut them more frequently than others. What factors explain these differences? Answers from anatomy researcher Michelle Moscova, from the University of New South Wales, Australia, in an article published in The Conversation.

The role of genetics and hormones

Genetics is the main factor. Familial traits directly influence the rate of division of hair and nail cells. For example, members of the same family, especially identical twins, often have similar growth rates.

Hormones also play a crucial role. During pregnancy, increased estrogen stimulates hair and nail growth, while menopause or chronic stress, associated with high cortisol levels, can slow this growth.

Age is another key factor: in young people, active metabolism promotes rapid cell division, which slows down with age.

The importance of nutrition

To grow, hair and nails need specific nutrients. Keratin, their main component, relies on an adequate intake of proteins, iron, zinc and vitamins. An iron deficiency can cause hair loss, while a zinc deficiency can weaken nails. A balanced diet is therefore essential to support their growth.

Hair and nails grow thanks to matrices located under the skin, recalls Michelle Moscova. For hair, the matrix cells divide at the base of the pilosebaceous follicles and gradually form the hair. The nails, for their part, are born in a matrix at the base of the nail, then slide on the richly vascularized nail bed.

Growth cycle variations

Hair growth follows a four-phase cycle:
-Anagen (growth), which can last up to eight years.
-Catagen (transition), where growth slows down.
-Telogen (rest), which precedes hair loss.
-Exogenous (renewal), with the appearance of a new hair.

Note that not all follicles follow this cycle simultaneously, thus avoiding temporary baldness. For nails, growth is more linear.

Finally, the researcher intends to demystify a preconceived idea: hair and nails do not grow after death. Dehydration of the skin can cause this illusion, but it is a purely visual phenomenon.