Analysis of factors influencing patch test reactions: Results from a large- population-based study in Chinese.

Background: Patch test, as a helpful tool in clinic diagnosis and safety assessment of cosmetics, is affected by many factors.

Objectives: To investigate the influencing factors of patch test reactions in a highly standardized large-scale dataset of Chinese.

Methods: 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.

Results: 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 (≥50 years old) was 30% more than the young group (<30 years old).

Conclusions: 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.