What is the medical term for gray hair?

The medical term for gray hair is "canities." This term is derived from Latin, where "canus" means gray or white, referring to the loss of pigmentation in the hair follicles as part of the natural aging process. As individuals age, the hair follicles gradually produce less melanin, the pigment responsible for hair color, resulting in gray or white strands.

In contrast, the other terms listed do not refer specifically to gray hair. "Melaniniasis" pertains to an abnormal accumulation of melanin in the tissues, which has no relation to the natural graying process. "Pheomelanin" is a type of melanin that contributes to lighter hair shades, such as red and blonde, but does not pertain to the graying of hair. "Trichorrhexis" refers to a hair condition where the hair shaft is brittle and prone to breakage, rather than a descriptor for the color of hair. Therefore, canities is the most accurate term to describe the phenomenon of gray hair.