Identity
Phloretin is a dihydrochalcone — a plant polyphenol — found in apple (fruit and bark). In cosmetics it is used under the INCI name Phloretin as an antioxidant active. Its profile is closely analogous to ferulic acid: a molecule best known not as a solo star but as a component of a designed antioxidant system, classically the phloretin + L-ascorbic acid + ferulic acid serum archetype.
Mechanism (as proposed)
Phloretin does two things. It is a potent free-radical scavenger — the antioxidant job — and it modulates membrane transport, which is proposed to help deliver co-formulated actives into skin. That second property is a large part of why it is paired with vitamin C: it supports both stability/defence and penetration of the system it sits in. The mechanism is well described. The honest limit is that the penetration-enhancement is a formulation rationale, not a proven standalone clinical outcome, and phloretin's poor solubility and stability mean it is almost always deployed inside a stabilised system rather than alone.
Reading the evidence honestly
Like ferulic acid, phloretin's strongest recognition is as a formula partner, and its standalone human data is thin — which is why the grade sits at C. The combination antioxidant serums it belongs to have real appearance-level support, but reading that onto isolated phloretin overstates the solo evidence. As with every antioxidant here, it supports the look of defended skin and complements, never replaces, sunscreen — and the pigment and photoprotection claims stay appearance-level.