Atopic dermatitis (AD) is a heterogeneous disorder. It is of different types and needs personalized medicine approaches. AD categorization occurs as the IgE-high, extrinsic subtype and the IgE-normal, intrinsic subtype. 

Although extrinsic AD is the major subtype containing skin barrier impairment (high incidence of filaggrin mutations), intrinsic AD occupies about 20% of AD with female dominance and preserved barrier. Extrinsic AD shows protein allergy and food allergy, while intrinsic AD displays metal allergy, possibly associated with suprabasin deficiency. In particular, collected food allergy knowledge has more evidently characterized extrinsic AD. 

Researchers have also proposed the European American (EA) and Asian AD subtypes. Asian patients with AD present a unique blended immune dysregulation and barrier feature phenotype between EA patients with AD and those with psoriasis. Another ethnic study suggests that filaggrin loss-of-function mutations are not prevalent in African American patients with AD, and Th1/Th17 attenuation and Th2/Th22 skewing occurs in these patients. 

Endotype is the molecular mechanism underlying the visible features/phenotype. Recent endotype classification gives new insights into AD and other allergic disorders. Endotype repertoire includes activation of type 2 cytokines, type 1 cytokines and IL-17/IL-22, impairment of epidermal barrier and abnormalities of intercellular lipids. There have been attempts to categorize endotype based on serum markers. This evidence point to a need for personalized or precision medicine appropriate for each subtype of AD.

Source: Tokura Y, Hayano S. Subtypes of atopic dermatitis: from phenotype to endotype. Allergol Int. 2022;71(1):14-24.