Identity
Ellagic acid is a polyphenol found in pomegranate, berries (raspberry, strawberry), walnuts and other plants, where it works as a defensive antioxidant. In cosmetics it is used under the INCI name Ellagic Acid as a brightening antioxidant — one of the plant-derived pigment actives, alongside the fungal (kojic acid) and berry/leaf (arbutin) options. It is best treated as the active, not as "pomegranate extract," which is a variable raw material.
Mechanism (as proposed)
Ellagic acid works on two fronts. As a tyrosinase inhibitor, it chelates the copper the enzyme needs to make melanin — the same copper-grabbing route kojic acid uses — damping pigment production. As a polyphenol antioxidant, it scavenges the free radicals generated by UV and pollution, which is the basis of its photoprotection-support and its anti-pigment effect (much UV pigmentation is oxidative). The dual mechanism is genuine and well described in the lab. The honest limiter is physical: ellagic acid is poorly water-soluble and penetrates skin variably, so a clean in-vitro result does not fully carry over to what reaches living skin.
Reading the evidence honestly
There is real human topical data — notably Japanese studies on UV-induced pigmentation and melasma appearance, where ellagic acid (often in "quasi-drug" whitening formulations) reduced the look of pigment over several weeks. But the studies are relatively small, frequently combination formulas, and the solubility/penetration issue tempers expectations — which is why the grade sits at C rather than higher. As with every brightener in this register, the measured endpoint is the appearance of existing pigment, not a lightening of baseline skin colour, and it is an adjunct to sunscreen, never a replacement.