Background: Dry air and cold weather have been shown to influence skin irritability. There is conflicting evidence concerning seasonal variability of irritant patch test results and there are no data concerning the influence of season on NaOH-induced irritation.
Patients and methods: A Swift Modified Alkaline Resistance Test (SMART) was carried out simultaneously on the volar forearm (FA) and the back of the hand (BOH) of 554 consecutive individuals (277 female, median age 36 years; 277 male, median age 42 years) who had previously had an occupational skin disease. The test comprises two challenges with 0.5 M NaOH each for 10 min. The clinical outcome in each patient was related to standardized data on the local ambient temperature (T) and absolute humidity (AH) on the day of examination obtained from the German Meteorological Service.
Results: Of the 554 patients, 212 (38.3%) showed a positive reaction on the FA, and 126 (22.7%) a positive reaction on the BOH. An atopic skin disposition significantly increased the odds for a positive clinical reaction on both the FA (OR 4.8, 95% CI 3.0-7.8) and the BOH (OR 3.1, 95% CI 1.8-5.5). In a logistic regression analysis a significant association between low T and AH, respectively, and clinical reactivity to NaOH on the BOH was found. The odds of a positive reaction were increased by 3.9 (95% CI 2.1-7.6) for an ambient T of < or =6 degrees C and by 2.9 (95% CI 1.6-5.7) for an AH of < or =8 mg l(-1). The effects of AH and T on the reactivity on the BOH were even more pronounced in atopic individuals. In contrast, there was no significant association between the test outcome on the FA and climatic parameters. Furthermore, the test outcome showed no significant association with duration of healing of hand eczema or eczema at other sites before the investigation. Moreover, there were no associations detectable between previous wet work load and NaOH reactivity on both the BOH and FA.
Conclusions: Unlike skin challenge with sodium lauryl sulphate, challenge with NaOH on a body area not directly exposed to environmental factors (FA) seems robust against seasonal influences. Furthermore, a NaOH test in this location (FA) may provide supporting evidence to help identify individuals with atopic skin. On the BOH, seasonal effects were demonstrated. Thus, when interpreting NaOH challenges on the BOH it would seem helpful to take ambient meteorological parameters into consideration.