Certain cutaneous viral infections, such as Herpes simplex, vaccinia and varicella infections are known to occasionally run an usually severe course in AD. Patients with AD display increased frequencies of recurrent cold sores and Herpes zoster and they also have increased antibody titers to Epstein-Barr virus. Heavy colonization of the skin with staphylococci and streptococci is common. The findings of increased severity and/or frequencies of these infections in AD may be explained by dysfunctional cell-mediated immunity and by cutaneous changes associated with AD. There is suggestive, but not any firm evidence, that infections play a causal role in the precipitation and exacerbation of AD. Infections are thus, in most cases, probably consequences rather than causes of the disease.