Why Our Hair Gets White?

Molecular Mechanism Behind Hair Graying

1. Melanocyte and Melanin Production: Hair color is determined by melanocytes found in the hair follicle’s bulb. These cells synthesize melanin in response to signals from surrounding cells, including keratinocytes. Two types of melanin contribute to hair color:

   • Eumelanin (black and brown pigments).
   • Pheomelanin (yellow and red pigments).

   Melanin production depends on the enzyme tyrosinase, which converts the amino acid tyrosine into melanin within the melanocytes. As we age, the number and function of these melanocytes gradually decline, leading to less melanin production and eventually white or gray hair.

2. Oxidative Stress and Mitochondrial Dysfunction: One major cause of melanocyte decline is oxidative stress. Hair follicles experience oxidative damage from reactive oxygen species (ROS), which are byproducts of cellular metabolism. Over time, oxidative damage accumulates due to reduced antioxidant defenses within the melanocytes. In particular, the enzyme catalase normally breaks down hydrogen peroxide (H₂O₂), a common ROS. With age, catalase levels decrease, leading to an accumulation of H₂O₂ in hair follicles. The buildup of hydrogen peroxide can inhibit tyrosinase and disrupt melanin synthesis, bleaching the hair from within.

   Studies show that mitochondrial dysfunction, which increases oxidative stress, also plays a significant role. The decline of mitochondrial function impairs the cell’s ability to manage oxidative damage, contributing to the depletion of melanocytes.

3. Genetics and Gene Expression: Genetic factors play a crucial role in determining when and how hair turns gray. Research has shown that genes like IRF4 and MITF are involved in regulating melanin production. Variations in these genes can influence the onset of graying. The Bcl2 gene, which regulates cell death, and MSX1, which controls melanocyte survival, are also associated with hair pigmentation.

   Additionally, Wnt signaling, which is critical for the regeneration of hair and the activation of melanocytes, becomes less efficient with age, further contributing to the graying process. The failure of the hair follicle’s stem cells to replenish melanocytes is another factor in age-related hair graying.