Smoking causes Premature Gray Hair: Nicotine Free Radicals damage the Melanocytes aka melanin-producing cells

 Smokers had earlier onset of hair graying (smokers: 31 (7.4) vs. nonsmokers: 34 (8.6), P = 0.034). Using multiple logistic regression with conditional likelihood, smokers were two and half times (95% CI: 1.5-4.6) more prone to develop PHG.

 Nicotine from smoking can build up in hair follicles and affect pigmentation.

Smokers’ hair: Does smoking cause premature hair graying?

 The possible mechanism of graying of hair could be explained on the basis of "free radical theory," which is analogous to the free radical theory of ageing.[⁵] The extraordinary melanogenic activity of melanocytes generates large amounts of reactive oxygen species through the hydroxylation of tyrosine and the oxidation of dihydroxyphenlyalanine (DOPA) to melanin. If not adequately removed by an efficient antioxidant system, an accumulation of these reactive oxidative species will generate significant oxidative stress. With ageing the antioxidant system becomes impaired leading to damage to the melanocyte itself from its own melanogenesis-related oxidative stress. Smoking often generates huge amounts of reactive oxygen species leading to increased oxidative stress. This pro-oxidant effect of smoking could lead to damage the melanin-producing cells, the melanocytes. This theory is supported by the observation that melanocytes in gray hair bulbs are frequently highly vacuolated, a common response to increased oxidative stress.[⁶]

 Tobacco and Gray hair