A longitudinal study on the correlation between faecal urease activity and incidence of nappy rash in infants

Introduction – Nappy (diaper) rash is a common skin condition experienced by most infants at least once during the first 2 years of life. Despite its prevalence, there is some debate over its pathogenesis. The objective of this study was to investigate whether a correlation exists between urease activity in infant faeces and the observed incidence of nappy rash (diaper dermatitis). This was explored in a longitudinal observational study of six infants conducted at a university childcare facility over 9 months. Methods – Six babies who met the inclusion criteria and attended Westwood Nursery, University of Bath, were recruited to the study with consent provided by parents following favourable ethical approval from the NHS Regional Ethics Committee. Soiled nappies, donated up to twice weekly, were analysed for urease activity in faecal bacteria. At the same time, nursery staff recorded the skin condition of the nappy area for participating infants. Results – Chi-squared analysis revealed a clear statistical correlation between urease expression and observed nappy rash incidence, as well as between the absence of faecal urease and healthy skin (P = <0.0002). Discussion – Urease-expressing bacteria were first implicated in the pathogenesis of nappy rash in the early 20th century. This is the first study to demonstrate a population-level correlation between nappy rash and faecal enzyme activity, which can be understood in terms of a causal chain: Urease catalyses ammonia production, which directly damages skin barrier function and creates a pH environment in which secondary opportunistic microorganisms can grow at an enhanced rate. This, in turn, increases skin-damaging enzyme activity, leading to more severe nappy rash.