Ergothioneine (EGT) is a naturally occurring, sulfur-containing amino acid and a potent antioxidant found in various foods, most notably mushrooms. While humans cannot synthesize it, our bodies have evolved a highly specific transporter (OCTN1 or ETT) to absorb and distribute it to tissues frequently exposed to oxidative stress, such as the eyes, liver, and red blood cells. Because it is essential for long-term health and levels decline with age, some researchers refer to it as a "longevity vitamin"