Megan A. Koster

1 month ago | health.harvard.edu | Hallie Levine |Megan A. Koster

March 12, 2025 By Hallie Levine, Health Writer Reviewed by Megan A. Koster, MD, PharmD, Contributor; Editorial Advisory Board Member, Harvard Health Publishing Mold is a type of fungus, a group of organisms that also includes yeasts and mushrooms. Mold thrives in wet places. Outdoors, it forms on damp surfaces like rotting logs or wet leaves. Inside, it can grow in damp areas like bathrooms, basements, or kitchens.