Background Atopic dermatitis (AD) is associated with elevated IgE levels and Th2 responses. The oral administration of nonpathogenic bacteria such as probiotics may improve the course of atopic diseases. It is believed that nonpathogenic bacteria prevent the development of allergic diseases by modulating intestinal immune responses. However, the effects of oral probiotics on AD could not be reproduced in all studies and the direct immunomodulation of the skin‐associated immune response by nonpathogenic bacteria has not yet been investigated.

Objectives We performed a prospective, double‐blind, placebo‐controlled clinical study with a cream containing a 5% lysate of the nonpathogenic bacteria Vitreoscilla filiformis.

Patients and methods Seventy‐five volunteers with AD (6–70 years of age) were randomized to receive either V. filiformis cream 5% or vehicle cream daily for 30 days. Efficacy was evaluated by the SCORe of Atopic Dermatitis (SCORAD), transepidermal water loss (TEWL), assessment of microflora, and the patient’s assessment of itch and loss of sleep.

Results Compared with placebo, V. filiformis lysate significantly decreased SCORAD levels (P =0·0044) and pruritus (P =0·0171). Active cream significantly decreased loss of sleep from day 0 to day 29 (P =0·0074). Qualitative and quantitative assessment of cutaneous microbial colonization revealed that V. filiformis lysate reduced Staphylococcus aureus colonization of the skin. The skin barrier as determined by TEWL also improved significantly with the cream alone.

Conclusions  V. filiformis lysate significantly improved AD. This may be in part due to reduction of S. aureus, but seems to relate in most parts to a direct immunomodulatory effect on skin‐associated immune responses.