Hair can be considered the frame of the face, and it is not new that humans have become concerned with its shape, hygiene, and especially its color. For thousands of years, humans have been dyeing their hair with henna to hide gray strands. Since then, humans have increasingly shown concern about the appearance of white hair.
White hair can appear as a consequence of various factors. The main one is aging. Others, such as exposure to UV radiation, X-rays, and psycho-emotional stress, can also lead to whitening. These factors can reduce the proliferation of melanocytes by decreasing the antioxidant activity of the cell and DNA repair. Aging and such aggressions cause oxidative stress in the hair follicle, leading to the accumulation of reactive oxygen species (ROS) that affect the melanocyte, as well as the regions where the stem cells of the hair follicle are located.
H2O2 (hydrogen peroxide) is one of the most recognized reactive oxygen species influencing the appearance of white hair. The negative effect depends on the concentration of H2O2 present. Low concentrations of hydrogen peroxide promote gene transcription and also enzymatic activity, capable of reducing its effect. But if too concentrated, this protection is not sufficient, and oxidative stress occurs. H2O2 is cleaved by the enzyme catalase, forming H2O and O2, and at high concentrations, it deactivates this enzyme. Low levels of catalase have been found in the hair follicles of white hair, and its activity has been seen to decrease in aged hair follicles.
Another factor that can have a significant influence on the appearance of white hair is the individual's genetic component. In 2005, researchers at Harvard University in the United States discovered that the emergence of gray hair is caused by a defect in the maintenance of melanocyte stem cells, which is accelerated by the deficiency of a protein called Bcl2, a regulator of apoptosis. The deficiency of this protein causes selective apoptosis of melanocyte stem cells, triggering differences in the presence of melanin, which consequently alters the color of the hair.
However, the appearance of white hair should not be seen as a sign of aging, but rather as a sign of maturity that is part of every human being's life.
Sources:
Schallreuter KU., Salem MMAEL, Hasse S, and Rokos H. The redox – biochemistry of human hair pigmentation. (2010) Pigment Cell Melanoma Res. 24; 51–62.
Nishimura EK, Granter SR, Fisher DE. Mechanisms of Hair Graying: Incomplete Melanocyte Stem Cell Maintenance in the Niche. (2005) SCIENCE Vol. 307 no. 5710 pp. 720-724.
