The consequences of smoking on hair health

Tony H. H. CHEN and Lin-Hui SU aimed to evaluate the association of androgenetic alopecia (AGA) with smoking and estimate its prevalence among Asian men, by implementing a questionnaire-based survey. Significant positive associations were observed between moderate or severe alopecia and smoking status with a relative risk of 1.77, current smoking of 20 or more cigarettes per day with a relative risk of 2.34, and smoking intensity with a relative risk of 1.78. Therefore, tobacco smoking would indeed be associated with hair loss.

The mechanisms by which smoking causes hair loss are multifactorial. Firstly, the skin's micro-circulation is narrowed by both acute and long-term smoking. Therefore, cells will not be sufficiently supplied with oxygen and nutrients, which can lead to hair loss.

Furthermore, the genotoxic compounds in smoke can damage the DNA of the hair follicle. Indeed, the reduction of capillary blood flow in the dermal papilla of hair follicles can also concentrate more toxic substances. Nicotine and cotinine are both detected in hair samples from smokers, and mutations in mitochondrial DNA associated with smoking have been observed in human hair follicles. These mutations can damage the follicles, leading to hair loss.

Finally, smoking can lead to oxidative stress. It induces the production of free radicals, which cause lipid peroxidation (or degradation), and subsequently triggers theapoptosis of hair follicle cells by upregulating genes related to this process. This could be one of the reasons why hair loss can be observed. Oxidative stress can also lead to the release of pro-inflammatory cytokines which, in turn, cause micro-inflammation and follicular fibrosis.