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Prof. Carlo Crosti, Clinica Dermatologica, Ospedale San Paolo, Via A Di Rudini, 8, I-20142 Milano (Italy) Despite its frequency, pompholyx or dyshidrotic eczema presents many unresolved problems of aetiology, pathogenesis and therapy. As its invariable histopatholog-ical picture of spongiotic dermatitis indicates, pompholyx is a non-specific reaction somehow related to the particular anatomy of the palmoplantar skin [1]. It may be, therefore, a manifestation of different pathologies such as atopic and contact dermatitis [2-4], oral allergy to metals [5, 6] and dermatophyte infection [7]. Rarely, even pemphigus and bullous pemphigoid may masquerade as dyshidrotic eczema [8, 9]. A recent paper has reviewed the available evidence and provided some new ones [10]. Age does not matter, as the disease is equally represented in the 16-40 and 41-65 age groups. Hands and feet may be involved in different ways. Pompholyx may affect either one hand or foot, both hands or both feet, or simultaneously hands and feet. Most patients have two homologous areas affected. Atopy is present in 50% of patients. The IgE serum level is frequently increased, irrespective of the family or personal history of atopy. Pompholyx may well be the first manifestation of atopy. Contact allergy to nickel plays an important role, especially considering that routine diagnostic procedures (patch tests with nickel sulphate) are probably insufficient to detect all of the allergic subjects. The high perspiration rate of the palms and soles favours a high concentration of metal salts (i.e. nickel) in these regions, which could be sufficient to cause an eczematous reaction. Further evidence comes from the oral provocation test with nickel salts: positivity is interpreted as a marker of latent hypersensitivity. In such cases, low-nickel diets have significantly improved the number and severity of pompholyx relapses. Other double-blind studies, however, did not find such a significant correlation. In subjects positive in the oral provocation test there may be an immune-complex-mediated reaction or a delayed hypersensitivity with false-negative patch tests, or even a non-immunological reaction. In the last instance, nickel salts could trigger a further unknown pathogenetic factor. Other contact allergens have been reported as significantly associated with pompholyx, namely carba-mix, dia-minodiphenylmethane, cobalt chloride and fragrance mix. Prick and intradermal tests with staphylococcal and other pyogenic bacteria antigens, dermatophytes and Candida have frequently been found positive. They are probably related to the prolonged contact with these microorganisms and not necessarily to actual infection. Likewise, house dust and pollens give frequent positive tests, but they have no apparent immunological correlation with an eczematous disease like pompholyx (type I vs. type IV hypersensitivity reaction). Acari may be a possible exception that deserves further investigation by patch tests with concentrated acaridic extracts.