Summary Background Seborrhoeic dermatitis is a chronic relapsing inflammatory skin disease with unclear pathophysiological mechanisms. Objectives To establish which lifestyle and physiological determinants are associated with seborrhoeic dermatitis. Methods Seborrhoeic dermatitis was diagnosed by a trained physician during a full‐body skin examination within the Rotterdam Study, a prospective population‐based cohort study in middle‐aged and elderly people. The current design is a comparative cross‐sectional study embedded in the Rotterdam Study. Potential factors were identified from the literature and analysed in a multivariable logistic regression, including: age, sex, obesity, skin colour, stress, depression, education level, hypertension, climate, xerosis cutis, alcohol and tobacco use. Results Of the 5498 participants, 788 participants were diagnosed with seborrhoeic dermatitis (14·3%). We found associations between seborrhoeic dermatitis and male sex adjusted odds ratio (OR) 2·09, 95% confidence interval (CI) 1·77–2·47, darker skin (adjusted OR 0·39, 95% CI 0·22–0·69), season (summer vs. winter: adjusted OR 0·63, 95% CI 0·48–0·82) and generalized xerosis cutis (adjusted OR 1·41, 95% CI 1·11–1·80). Conclusions Seborrhoeic dermatitis is one of the most common inflammatory dermatoses in middle‐aged and elderly individuals, especially during winter. Men, and people with a light and dry skin were most likely to have seborrhoeic dermatitis. What's already known about this topic? Seborrhoeic dermatitis is a common chronic relapsing inflammatory skin disease with unclear pathophysiological mechanisms. Numerous host and environmental factors have been implicated in the pathogenesis of seborrhoeic dermatitis, but most have not been validated. What does this study add? Male sex, light skin colour, the season winter and generalized dry skin increased the likelihood of having seborrhoeic dermatitis. Interventions aiming to improve skin‐barrier function could become a target in the treatment of patients with seborrhoeic dermatitis. Linked Comment: Drucker and Doiron. Br J Dermatol 2018; 178:22–23. Plain language summary available online Respond to this article