Revisiting the polar paradox theory: a critical overview.

The polar paradox is a theory that illustrates the paradoxical behavior of antioxidants in different media and rationalizes the fact that polar antioxidants are more effective in less polar media, such as bulk oils, while nonpolar antioxidants are more effective in relatively more polar media, such as oil-in-water emulsions or liposomes. For 2 decades since it was proposed, the theory has been used to interpret results in antioxidant efficiency studies. However, more recently, new evidence from more comprehensive assessments has emerged that contradicts the polar paradox theory, hence necessitating its re-evaluation. More complex factors in addition to polarity must be taken into account to explain antioxidant efficacy.