At the beginning of the 20th century, investigators assumed that ammonia released from the urine was the primary irritant in napkin dermatitis [2,3]. In 1921 Cooke named Bacterium ammoniagenes as responsible for napkin dermatitis, which was thus named ammoniacal dermatitis . His well-argued theory was generally accepted for decades. Further studies showed, however, the same incidence of urea-splitting bacteria in the napkins of babies with and without rash. In 1977, Leyden et al. proved that ammonia did not cause skin irritation when patch tested on the skin of adults and children . They observed no irritation even when the concentrations of ammonia were much higher than those with ‘ammoniacal diapers’. Investigations in the 1980s showed that the aetiology of napkin dermatitis was more complex and different from that thought previously [6,7].