This is best defined by IL‐17A, the most studied IL‐17 family member, which has been shown to contribute to dermatitis,26, 27 psoriasis,28 IBD,29, 30 arthritis,31 multiple sclerosis (MS),32 periodontal disease6, 7 and systemic lupus erythematosus,33 among other inflammatory diseases. This evidence concerns the gene IL17A and psoriasis.