Ergothioneine

A naturally occurring sulphur-containing histidine derivative synthesised exclusively by certain fungi and mycobacteria — humans cannot make it, but skin and other tissues express a dedicated transporter (OCTN1 / SLC22A4) that concentrates dietary ergothioneine specifically in oxidatively stressed sites. The thione-thiol tautomer provides exceptional ROS quenching, particularly hydroxyl radicals and singlet oxygen, while resisting auto-oxidation (it doesn't behave like a classical antioxidant pro-oxidant under physiological conditions). Bruce Ames's 'longevity vitamin' framing reflects evidence linking low ergothioneine status to age-related disease incidence.

0.1–1% (Mibelle MitoPro biotech-derived at the high end)

Effective at 0.1–1% in serums and creams. Stable, compatible with virtually any system. Pairs with niacinamide, peptides, and vitamin C.

Cost — fermented ergothioneine is expensive, and some 'ergothioneine' claims use sub-active doses. Long-term clinical skin data is still maturing.

Cost is the principal constraint — fermented ergothioneine is genuinely expensive and 'contains ergothioneine' on a label commonly means sub-active dosing. The OCTN1 skin-transporter logic is sometimes oversold into 'specifically targets aged cells', which oversimplifies what is a tissue-distribution finding, not a senescence-selective one.

Sold as the longevity-skincare frontier antioxidant. Honest position: a genuinely excellent and well-targeted antioxidant active with strong mechanistic credentials and maturing topical clinicals — worth the cost in formulations that dose it meaningfully, performative in those that don't.