The lipophilic environment encircles the lipophilic low-molecular-weight antioxidants (α-tocopherol, β-carotene, and Ubiquinol) and prevents them from reacting as skin protectors.
Oxidative stress is defined as a disturbance in the prooxidant-antioxidant balance in favor of the former and has been suggested to be a relevant factor in aging as well as in different pathological conditions, such as heart attack, diabetes, and cancer. Ubiquinol is very sensitive against oxygen radicals and gives ubiquinone as an oxidation product. Therefore, the ratio of ubiquinol to ubiquinone should be a good marker of oxidative stress because of its definition.

The oxidized (UQox) and reduced (Ubiquinol) forms of ubiquinone (UQ) homologues in rat tissues and subcellular fractionsare analyzed. The levels of these homologues are highest in heart with lesser amounts occurring in kidney, liver and other organs. In liver and blood plasma, the UQred homologue amounted to 70-80% of the total UQ (UQox + Ubiquinol = t-UQ). Ubiquinol is less than 30% of t-UQ in other tissues and blood cells. t-UQ is much higher in leukocytes and platelets in blood than in erythrocytes. In erythrocytes, t-UQ is exclusively located in the cell membranes.Ubiquinol is also found in all subcellular fractions isolated from liver and kidney in about the same ratio as Ubiquinol/t-UQ is present in the whole organ. The levels of Ubiquinol per mg protein in subcellular fractions from liver is highest in mitochondria, with lesser amounts present in plasma membranes, lysosomes, Golgi complex, nuclei, microsomes and cytosol. In the mitochondria, the outer membranes are richer in t-UQ than the inner membranes.