Nevus comedonicus is an uncommon skin abnormality comprised of groups of pits in the skin filled with black keratinous plugs. QUESTION Ringworm is caused by a fungus. See Answer From Skin Problems and Treatments Resources What You Should Know About PsoriasisIs Your Skin Trouble Blocked Hair Follicles?Is It Dry Skin Or Atopic Dermatitis? Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19 References Jameson, J. Larry, et al. Harrison's Principles of Internal Medicine, 20th Ed. New York: McGraw-Hill Education, 2018.