Background In atopic dermatitis (AD) patients, the intestinal mucosal barrier function is weakened, permiting frequent invasion by antigens. Polyamines and short‐chain fatty acids (SCFA) produced by intestinal bacteria are involved in the promotion of intestinal mucosal barrier functions.

Aim Our aim was to investigate the effect of pro‐biotic yogurt containing Bifidobacterium animalis subsp. lactis LKM512 (LKM512 yogurt) on subjective symptoms, intestinal microbiota, intestinal bacterial metabolites (polyamines and SCFA), and T‐helper type 1 (Th1)/Th2 balance in intractable AD patients.

Methods In a double‐blind, placebo‐controlled, crossover study, LKM512 yogurt was given for 4 weeks to 10 adult AD patients who were diagnosed with moderate AD (four males and six females; average age, 22.1 years). The subjective symptoms were recorded after each intervention. The dynamics of fecal microbiota were analysed by the terminal‐restriction fragment length polymorphism method. The effects of LKM512 yogurt on fecal polyamines, SCFA, and serum cytokines were evaluated.

Results Scores of itch and burning tended to improve to a greater extent by LKM512 yogurt consumption than by placebo consumption. LKM512 yogurt (P<0.005) and placebo consumption (P<0.05) significantly increased the serum IFN‐γ concentration by six‐ and threefold, respectively. Fecal microbiota was altered dynamically by LKM512 yogurt consumption, in particular, the bacterial species and phylotypes of Bifidobacterium, Clostridium cluster IV and subcluster XIVa were increased in number. In addition, fecal spermidine concentration was significantly (P<0.05) increased, while fecal butyrate also tended to be increased by LKM512 yogurt consumption.

Conclusion We conclude that LKM512 yogurt consumption may be effective against intractable adult‐type AD and this effect depends on the recovery of the intestinal mucosal barrier function and the induction of the Th1‐type cytokine by polyamines and SCFA, particularly, butyrate, produced by the altered intestinal microbiota.