Psoriasis is a chronic inflammatory skin disease associated with an increased risk of developing cardiovascular disease. Various environmental factors contribute to disease development in genetically susceptible individuals. Although infections have been associated with disease initiation and recurrence, the consequences of early exposure to infections, many years before disease manifestation, is unexplored. To investigate the effect of exposure to infections during formative years on the incidence of psoriasis through to early adulthood. ABIS is a large birth cohort in which parents of participating children have answered comprehensive questionnaires on exposure to infections and medication at different age intervals of the children. Information regarding psoriasis was obtained from the Swedish National Patient Register, while data on medication was obtained from the National Prescribed Drug Register. Statistical analyses were performed with custom-written R scripts. Logistic regression analysis on one-year follow-up data revealed that influenza was associated with an increased risk of developing psoriasis later in life (OR 2.47, CI 1.32-4.39; P= 0.006). In line with this, at the third-year evaluation, we found that participants who had tonsillitis at least once during the first three years of life had almost three times greater risk of developing psoriasis into early adulthood compared to controls (OR 2.90, CI 1.46-5.56; P= 0.003). In contrast, at the eight-year evaluation, we found that psoriasis was less frequent in children who had experienced gastroenteritis episodes between ages six and eight, compared to controls (OR 0.42, CI 0.20-0.92; P =0.0028). We demonstrate for the first time the effect of exposure to infections during the first years of life, and their role in the subsequent development of psoriasis extending into early adulthood. Our study indicates that early exposure to infections may influence the development of the adaptive immune system during formative years. This modulation is evidenced by the higher incidence of psoriasis observed in early adulthood, several years after the initial exposure.
