What causes hair to turn gray or white?

Hair turns gray or white primarily due to a loss of pigment in the hair follicle. The color of hair is determined by the presence of melanin, which is produced by melanocytes located in the hair bulb. As people age, the melanocytes gradually decrease in number or cease to function, leading to a reduction in melanin production. This lack of pigment results in hair becoming gray or white.

Additionally, the presence of air bubbles in the medulla, the innermost layer of the hair shaft, can contribute to the change in appearance. When the melanocytes stop producing pigment and air becomes trapped in the medulla, it can make the hair appear lighter, further contributing to the graying process.

While genetic predisposition may influence the age at which hair turns gray, the core mechanism involves the loss of pigment and the introduction of air into the hair structure itself. The combination of these factors leads to the gray or white appearance of hair as people age.