The Role of Yeast in Atopic Dermatitis Revisited: a Critical Appraisal

Atopic dermatitis (AD) is the commonest chronic inflammatory skin disorder. In a subset of patients, particularly those with symptoms predominating on the head and neck, the yeast Malassezia is thought to be an important driver of AD of a more recalcitrant nature. Mechanistically, sensitization to Malassezia appears mediated by antigen-presenting cells in eczematous skin that promote cutaneous inflammation, partly through cross-reactivity with auto-antigens. This is consistent with evidence that patients with head and neck dermatitis (HND) have higher rates of sensitization to Malassezia versus healthy controls. However, to prove that Malassezia is a causative factor in HND, we should evaluate evidence on whether efforts to reduce Malassezia actually improve disease activity. We therefore performed a systematic review of randomized controlled trials (RCTs) investigating antifungal treatments in AD/HND. The majority of RCTs concluded that antifungals were superior to placebo or standard treatment in terms of reducing AD severity, supporting the notion that yeast can contribute to eczematous skin inflammation. Recognising and treating yeast colonization in AD patients can result in a significant reduction in disease severity, in addition to anti-inflammatory therapy alone.