No / Background  Interleukin (IL)-33 is a member of the IL-1 family and has been implicated in Th2-driven allergic diseases such as atopic dermatitis (AD) and asthma. The principal Th2 cytokine IL-4, found highly expressed in acute allergic eczema, is known to downregulate human β-defensin 2 (hBD2) expression in human keratinocytes and this is associated with superinfection in patients with AD. Objectives  To investigate the effect of IL-33 on the expression of hBD2 in human keratinocytes. Methods  hBD2 production by stimulated keratinocytes was measured by enzyme-linked immunosorbent assay. Results  Our results showed that serum is a very potent inducer of hBD2 and 2·5% human serum was much more potent in inducing hBD2 than 20 ng mL−1 of tumour necrosis factor-α. Interestingly, serum from patients with AD showed an impaired ability to induce hBD2 in normal keratinocytes. IL-33 significantly downregulated serum-induced hBD2. The downregulatory capacity of IL-33 was found to be 1·5- to 2-fold weaker compared with IL-4. Conclusions  Our data suggest that IL-33 can significantly contribute to the decreased expression of hBD2 in acute eczematous reaction clinically characterized by spongiosis and oozing – thus indicative for contact of the epidermis with serum components.