Abstract Background Studies on the association between severity of atopic dermatitis (AD) and lifestyle factors in adults have not been conducted in the Netherlands to date. Aim To explore the association between moderate to severe AD and lifestyle factors in adults in the Dutch general population. Methods We conducted this cross-sectional study within the Lifelines Cohort Study by sending a digital AD questionnaire to 135 950 adults in 2020. We extracted data on lifestyle factors from baseline, collected between 2006 and 2013. We analysed the association between lifestyle factors and presence of AD of any severity and of moderate to severe AD, using binary logistic regression and linear regression models. Results We enrolled 56 896 participants (mean age 55.8 years, 39.7% males). The lifetime prevalence of self-reported physician-diagnosed AD was 9.1%, and the point prevalence of any AD and of moderate to severe AD was 3.3% and 2.3%, respectively. We found that moderate to severe AD was associated with smoking habit of > 15 pack-years, alcohol consumption of > 2 drinks per day, chronic stress, Class I obesity, and both shorter and longer sleep duration. Moreover, we found dose–response associations with increases in smoking pack-years and level of chronic stress. We observed no associations with abdominal obesity, physical activity, diet quality or a vegetarian/vegan diet. Conclusion We found associations between moderate to severe AD and some modifiable lifestyle factors. Our findings indicate that more screening and counselling for lifestyle factors, particularly smoking, alcohol use, stress, obesity and sleep disturbances, appears warranted in patients with moderate to severe AD. Further longitudinal studies are required to better characterize the direction of these associations and to develop strategies for prevention.