Atopy-related skin rash in a normal population of infants: Distribution and rates for 50 separate skin regions: Cohort study from 4 months to 3.5 years

Analysis of the rash in a normal population of infants may give new information that is different from clinical observation of atopic dermatitis (AD). For this purpose, a cohort study was undertaken on infants at 4months, 10months and 3.5years. Infants who attended the local health center for health check were the subjects. Rash related to AD, dryness, scaling, erythema, papules, exudation and crusts was recorded in 50 skin regions and divided into three degrees. Examination was performed twice a month for a year at each age. The 777 infants who attended all three examinations were analyzed in this report. Rash-positive regions were 14.7% on average at 4months and decreased with age. Prevalence of rash-positive infants was 93.6% at 4months and also decreased with age. The main findings are as follows. First, rash was more frequent and more severe in younger infants. This seems to suggest that AD in early infancy is initiated and developed by immune immaturity, and is resolved by its maturation. Second, rash involved preferentially air-exposed and air-closed skin in younger infants. This seems to be evidence that the epidermis of young infants is easily responsive to both dryness and wetness. Third, some regions did not show age-dependent reduction of rash rate in younger infants. Those regions are probably irritated by saliva and urine or rubbing and scratching.