Identity
Mangiferin is a xanthonoid — a polyphenol built on a xanthone core — found most famously in mango (Mangifera indica), and also in other plants. In cosmetics it is used under the INCI name Mangiferin as a plant antioxidant. (It is also marketed as an ingestible supplement for metabolic and other effects — that use is outside this register's topical scope.)
Mechanism (as proposed)
Mangiferin is a potent free-radical scavenger in the lab, with well-described antioxidant and anti-inflammatory activity, and some in-vitro reports of effects on melanin pathways. The laboratory pharmacology is genuinely strong — the recurring trap for plant polyphenols. Two practical limits temper it on skin: mangiferin is poorly water-soluble, carries a yellow tint that complicates formulation, and penetrates skin uncertainly, so a clean in-vitro result does not fully carry to living tissue.
Reading the evidence honestly
The decisive gap is the missing study type: there is little controlled human topical data on mangiferin for any skin outcome. The cosmetic case rests on in-vitro antioxidant and anti-inflammatory results, and "potent antioxidant in a dish" has a poor record of translating to visible human benefit — hence the D grade despite a strong laboratory profile. Where mangiferin has a larger evidence base, it concerns ingestible metabolic and anti-inflammatory effects, which this topical register does not cover.