Biologic and Small Molecule Therapies for Moderate to Severe Psoriasis: Focus on Psoriasis Comorbidities BioDrugs Springer Nature Link Alterations of the Skin and Gut Microbiome in Psoriasis and Psoriatic Arthritis Many treatment guidelines for psoriasis rely heavily on body surface area (BSA) involvement to determine disease severity and eligibility for systemic therapies like biologics. Traditionally, patients with less than 10% BSA involvementespecially Psoriasis Nature Reviews Disease Primers