BACKGROUND: Although eczema affects 2-20% of children worldwide, there is little direct evidence on the role of environmental factors in disease flares. OBJECTIVES: We sought to identify which environmental factors might worsen eczema. METHODS: Sixty children aged 0-15 years with eczema were studied intensively for up to 9 months. Daily electronic diaries and portable data loggers were used to record indoor exposures, and external meteorological data were obtained from a local monitoring centre. The primary outcome was a daily 'bother' score. Autoregressive moving average models were used to study the impact of exposures on eczema severity for individuals. Random effects modelling pooled estimated regression coefficients across participants. RESULTS: Increased severity was associated with nylon clothing [pooled regression coefficient 0.23, 95% confidence interval (CI) 0.03-0.43], dust (0.53, 0.23-0.83), unfamiliar pets (0.22, 0.10-0.34), sweating (0.24, 0.09-0.39) and shampoo (0.07, 0.01-0.14). The latter was enhanced in cold weather (0.30, 0.04-0.57). Body-site specificity was observed for nylon clothing, (trunk P =0.02, limbs P = 0.03), wool clothing (trunk P = 0.03, but not limbs P = 0.62) and unfamiliar pets (hands P < 0.001). A combination of any three of seven likely variables was associated with disease worsening (pooled regression coefficient 0.41, 95% CI 0.20-0.63). CONCLUSIONS: This exploratory study suggests that nylon clothing, dust, unfamiliar pets, sweating and shampoos may play a direct role in worsening eczema in children with eczema. Combinations of exposures acting in concert may also be important. Such knowledge may be useful to families with eczema and could lead to better strategies for preventing flares.