Patch test, as a helpful tool in clinic diagnosis and safety assessment of cosmetics, is affected by many factors. To investigate the influencing factors of patch test reactions in a highly standardized large-scale dataset of Chinese. Patch test data (n=151,280) from safety assessments of cosmetic products were obtained following internationally standardized patch testing protocols during 2004-2017 in China. The frequency of patch test reactions was 1.45% (2,191/151,280), with majority of the reactions being "score 1" reactions (also known as doubtful reactions, n=2,075) and a small number being "score 2" reactions (weak reactions, n=116). Patch test reactions were 67% more frequent in winter (p<0.001), associated with temperatures (p<0.001), rather than relative humidity (P:0.29). The frequency of reactions was higher in men than in women (p:0.001), especially in winter. The risk to develop reactions clearly increased with age in women (p<0.001), but not in men (p:0.14). In women, the frequency of reactions in the old group (≥50years old) was 30% more than the young group (<30years old). The frequency of patch test reactions to cosmetic products was 1.45% in our large-scale study. The influencing factors of patch test include season, sex, and age, which should be considered when conducting and interpreting patch testing.
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