Exploration of the effects of classroom humidity levels on teachers’ respiratory symptoms

PURPOSE: Previous studies indicate that teachers have higher asthma prevalence than other non-industrial worker groups. Schools frequently have trouble maintaining indoor relative humidity (RH) within the optimum range (30-50%) for reducing allergens and irritants. However, the potential relationship between classroom humidity and teachers’ health has not been explored. Thus, we examined the relationship between classroom humidity levels and respiratory symptoms among North Carolina teachers. METHODS: Teachers (n=122) recorded daily symptoms, while data-logging hygrometers recorded classroom RH levels in 10 North Carolina schools. We examined effects of indoor humidity on occurrence of symptoms using modified Poisson regression models for correlated binary data. RESULTS: The risk of asthma-like symptoms among teachers with classroom RH >50% for five days was 1.27 (0.81, 2.00) times the risk among the referent [teachers with classroom RH 30-50%]. The risk of cold/ allergy symptoms among teachers with classroom RH >50% for five days was 1.06 (0.82, 1.37) times the risk among the referent. Low RH (<30%) for five days, was associated with increased risk of asthma-like [Risk Ratio (RR): 1.26 (0.73, 2.17)] and cold/allergy symptoms [RR: 1.11 (0.90, 1.37)]. CONCLUSIONS: Our findings suggest that prolonged exposure to high or low classroom RH was associated with modest (but not statistically significant) increases in the risk of respiratory symptoms among teachers