In a case-control study of patients with HS, we evaluated the associations between the use of 5 mg folic acid (FA) daily and serum concentrations of folate, unmetabolized folic acid (UMFA), interleukin (IL)-6, IL-8, IL-10, interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α); and mRNA expression of <i>dihydrofolate reductase</i> (<i>DHFR</i>), <i>methylene tetrahydrofolate reductase</i> (<i>MTHFR</i>), <i>IL8</i>, <i>IFNG</i> and <i>TNFA</i> genes.