Ergothioneine is a naturally occurring sulfur-containing amino acid derivative of histidine that acts as a potent antioxidant. Produced exclusively by certain bacteria and fungi, it is acquired by humans and animals exclusively through dietary sources such as mushrooms. It is actively transported into cells via the OCTN1 transporter and accumulates in tissues prone to oxidative stress. Ergothioneine scavenges reactive oxygen and nitrogen species, protects cellular components including DNA, proteins, and lipids, and exhibits anti-inflammatory properties. Research indicates potential benefits in mitigating neurodegenerative diseases, cardiovascular conditions, and UV-induced skin damage due to its stable thione tautomer that remains effective at physiological pH.