Psoriasis is a chronic inflammation of the skin. Bacterial infections as tonsillits are known trigger factors for psoriasis. In this project we are investigating whether the abundance of different bacterial genera (skin microbiome) and genetic variations (single nucleotide polymorphisms, SNPs)) contribute to the severity of psoriasis. The analysis will account for covariates as sex, age, smoking, alcohol intake and body mass index. Our hypothesis is, that a certain combination of SNPs and skin microbiome increase psoriasis severity.