Background: Despite previous attempts to classify atopic dermatitis (AD) into subtypes (e.g. extrinsic vs. intrinsic), there is a need to better understand specific phenotypes in adulthood., Objectives: To identify, using machine learning (ML), adult AD phenotypes., Methods: We used unsupervised cluster analysis to identify AD phenotypes by analysing different responses to predetermined variables (age of disease onset, severity, itch and skin pain intensity, flare frequency, anatomical location, presence and/or severity of current comorbidities) in adults with AD from the Danish Skin Cohort., Results: The unsupervised cluster analysis resulted in five clusters where AD severity most clearly differed. We classified them as 'mild', 'mild-to-moderate', 'moderate', 'severe' and 'very severe'. The severity of multiple predetermined patient-reported outcomes was positively associated with AD, including an increased number of flare-ups and increased flare-up duration and disease severity. However, an increased severity of rhinitis and mental health burden was also found for the mild-to-moderate phenotype., Conclusions: ML confirmed the use of disease severity for the categorization of phenotypes, and our cluster analysis provided novel detailed information about how flare patterns and duration are associated with AD disease severity., Competing Interests: Conflicts of interest Outside the submitted work, S.F.T. has been a speaker or advisor for Sanofi, AbbVie, LEO Pharma, Pfizer, Eli Lilly, Novartis, UCB Pharma, Almirall and Janssen Pharmaceuticals; and has received research support from Sanofi, AbbVie, LEO Pharma, Novartis, UCB Pharma and Janssen Pharmaceuticals. Outside of the submitted work, A.E. has received research funding from Pfizer, Eli Lilly, Novartis, Bristol Myers Squibb, AbbVie, Janssen Pharmaceuticals, Boehringer Ingelheim, the Danish National Psoriasis Foundation, the Simon Spies Foundation and the Kgl Hofbundtmager Aage Bang Foundation; and has received honoraria as consultant and/or speaker from Amgen, AbbVie, Almirall, LEO Pharma, Zuellig Pharma, Galápagos, Sun Pharmaceuticals, Samsung Bioepis, Pfizer, Eli Lilly, Novartis, Union Therapeutics, Galderma, Dermavant, UCB, Mylan, Bristol Myers Squibb, McNeil Consumer Healthcare, Horizon Therapeutics, Boehringer Ingelheim and Janssen Pharmaceuticals. Outside of the submitted work, J.P.T. is an advisor for AbbVie, Almirall, Arena Pharmaceuticals, Coloplast, OM Pharma, Aslan Pharmaceuticals, Union Therapeutics, Eli Lilly, LEO Pharma, Pfizer, Regeneron and Sanofi-Genzyme; is a speaker for AbbVie, Almirall, Eli Lilly, LEO Pharma, Pfizer, Regeneron and Sanofi-Genzyme; and has received research grants from Pfizer, Regeneron and Sanofi-Genzyme. J.P.T. is an employee of LEO Pharma. Outside the submitted work I.V. has received research funding from Sanofi/Regeneron Pharmaceuticals, Pfizer and AbbVie; personal honoraria from Pfizer for lecturing; and has been a subinvestigator for LEO Pharma. Outside the submitted work, A.-S.H. has received honoraria from LEO Pharma (speaker) and Coloplast (consultant). L.N. and M.-L.N. declare no conflicts of interest., (© The Author(s) 2023. Published by Oxford University Press on behalf of British Association of Dermatologists. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)