Here's why:
* Pigment Production: Human hair color is determined by the amount and type of melanin pigment produced by melanocytes in hair follicles. Melanin comes in two forms: eumelanin (brown/black) and pheomelanin (red/yellow). There's no natural pigment that produces purple.
* Genetic Basis: Hair color is largely determined by genetics, and there's no known gene variant that results in purple hair.
* Rare Conditions: While some conditions can alter hair color (like albinism or vitiligo), they don't produce purple.
So, if you see someone with purple hair, it's almost certainly due to hair dye!