Ergothioneine is a rare antioxidant found in mushrooms—especially white button (Agaricus bisporus), shiitake (Lentinula edodes), and king oyster (Pleurotus eryngii)—that’s absorbed in your body through a special transporter protein. It targets areas of high oxidative stress (like the brain and heart) and helps protect cells from inflammation, aging, and disease. Animal studies show it may support memory, reduce damage from diabetes, and even protect joints. While clinical research is still emerging, its natural stability and bioavailability have led some scientists to call it a “longevity vitamin.”