Identification of factors associated with minimal erythema dose (MED) variations in a large‐scale population study of 22,146 subjects

BACKGROUND: Minimal erythema dose (MED) has substantial inter intraindividual variations, reflecting the influence of very diverse factors. However, related studies showed little consistency probably because of their limited sample size. OBJECTIVE: To identify the factors associated with MED variations in a large-scale population study. METHODS: The MED test was performed by following the international standard procedure on 22 146 subjects. The results were analysed in adjusted multivariable linear and logistic regression models. RESULTS: This large-scale study revealed that lower MED was consistently associated with lighter skin [beta-coefficient = -0.33, 95% confidence interval (CI) -0.36 to 0.30, P = 6.41 x 10(-84) ]. Females had significantly higher MED than male (beta = 0.91, 0.32-1.50, P = 2.93 x 10(-3) ). Stratified analyses showed that MED was not associated with age [female: odds ratio (OR) = 0.99, 0.98-1.01; male: OR = 0.99, 0.97-1.00]. MED was lower in summer than in other seasons (spring: OR = 1.08, 1.06-1.11; autumn: OR = 1.11, 1.08-1.13; winter: OR = 1.20, 1.18-1.22). Furthermore, MED was associated with air temperature (beta = -0.36, -0.49 to 0.23, P = 4.81 x 10(-8) ) and air pressure (beta = -0.64, -0.82 to 0.46, P = 8.01 x 10(-12) ) in summer only while not in other seasons. CONCLUSIONS: This study provides unprecedented evidence that MED is associated with skin colour, sex, season and meteorological factors, but not with age.