Hidradenitis suppurativa and atopic dermatitis: A 2-way association

Background: The coexistence of hidradenitis suppurativa (HS) and atopic dermatitis (AD) had been reported but, to our knowledge, was not investigated in controlled studies. Objective: To evaluate the bidirectional association between HS and AD. Methods: A population-based retrospective cohort study was conducted to compare the incidence rate of AD among patients with HS (n = 6779) and age-, sex-, and ethnicity-matched control individuals (n = 33,260). Adjusted hazard ratios (HRs) and adjusted odds ratios were estimated. Results: The incidence of AD was 2.51 (95% confidence interval [CI], 2.07-3.02) and 1.24 (95% CI, 1.10-1.40) per 1000 person-years among patients with HS and control individuals, respectively. Patients with HS were twice as likely to develop AD as control individuals (HR, 2.06; 95% CI, 1.64-2.58). Furthermore, the prevalence of pre-existing AD was higher in patients with HS than in control individuals (2.5% vs 1.8%, respectively; P < .001). A history of AD was associated with a 40% increase in the odds of HS (odds ratio, 1.41; 95% CI, 1.19-1.67). Relative to patients with isolated HS, those with a dual diagnosis of HS and AD were younger and had a female predominance, lower prevalence of smoking, and lower body mass index. Limitations: Retrospective data collection. Conclusions: A bidirectional association between HS and AD was observed. Dermatologists should be aware of this association.