Hidradenitis suppurativa and atopic dermatitis: A 2-way association

The coexistence of hidradenitis suppurativa (HS) and atopic dermatitis (AD) had been reported but, to our knowledge, was not investigated in controlled studies.To evaluate the bidirectional association between HS and AD.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.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.Retrospective data collection.A bidirectional association between HS and AD was observed. Dermatologists should be aware of this association.