Why does hair turn gray?
Hair turns gray when the pigment cells in hair follicles, called melanocytes, slow down and stop making melanin. This mostly happens with age and is strongly influenced by genes.
Each hair grows from a follicle that contains pigment-producing cells. As we age, the stem cells that replace these pigment cells gradually decline. New hairs grow in with less melanin and look gray, and hairs with no melanin at all look white. Gray hair is really a mix of colored and white strands.
The age when hair turns gray depends largely on genetics and ancestry. Many people of European descent start to go gray in their mid-thirties, while it tends to start later in people of Asian and African descent. Smoking, some medical conditions and lack of vitamin B12 can cause earlier graying.
Can stress turn hair gray?
A 2020 study in mice found that sudden stress can damage the stem cells that supply pigment, causing gray hair. A 2021 study in humans found that hairs could temporarily regain color when stress was reduced. However, the story of hair turning white overnight is very unlikely.
Did You Know?
Hair does not change color once it has grown from the scalp. A gray hair grows that way from the root; existing colored hair cannot suddenly turn gray.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.