Forearm hair density and risk of keratinocyte cancers in Australian adults.

Evidence suggests that progenitor cells of keratinocyte cancers (basal cell carcinoma (BCC) and squamous cell carcinoma (SCC)) may originate from epidermal stem cells including hair follicle stem cells. We hypothesised that, therefore, a relatively higher density of hair follicles on human skin may increase keratinocyte cancer risk. To evaluate this, we assessed density of mid-forearm hair in Australian adults who were randomly selected participants in a community-based cohort study of skin cancer. Hair density was assessed clinically against a set of four standard photographs showing grades of hair density, and incidence data on histologically confirmed BCC and SCC across a 20-year period were collected. Incidence rate ratios were calculated for categories of forearm hair density using multivariable regression analysis with adjustment for age, sex, phenotypic characteristics and markers of chronic sun exposure. Among the 715 participants (43 % male, average age 61 years), 237 developed at least one BCC and 115 persons developed at least one SCC. Participants with dense forearm hair (n = 169, all male) had a higher incidence of BCC (IRR = 2.24, 95 % CI 1.20, 4.18, P = 0.01) and SCC (IRR = 2.80, 95 % CI 1.20, 6.57, P = 0.02) compared to individuals with sparse forearm hair after multivariable adjustment. Stratified analyses showed that among men, those with dense versus sparse hair developed SCC more commonly (IRR = 3.01, 95 % CI 1.03, 8.78, P = 0.04). Women with moderate versus sparse hair density were more likely affected by BCC (IRR = 2.29, 95 % CI 1.05, 5.00, P = 0.038). Thus, our study suggests that in both men and women, a higher density of body hair may be associated with increased BCC and SCC risk.