Benzoic acid drinks (phosphoric acid), pickles (vinegar) or other acidified food are preserved with benzoic acid and benzoates. Typical levels of use for benzoic acid as a preservative in food are between 0.05–0.1%. Foods in which benzoic acid may be used and maximum levels for its application are controlled by local food laws. Concern has been expressed that benzoic acid and its salts may react with ascorbic acid (vitamin C) in some soft drinks, forming small quantities of benzene. Benzoic acid is a constituent of Whitfield's ointment which is used for the treatment of fungal skin diseases such as tinea, ringworm, and
Vitamin C and also regenerator of other antioxidants. Plants use multiple pathways to synthesize vitamin C. The major pathway starts with glucose, fructose or mannose (all simple sugars) and proceeds to L-galactose, L-galactonolactone and ascorbic acid. There is feedback regulation in place, in that the presence of ascorbic acid inhibits enzymes in the synthesis pathway. This process follows a diurnal rhythm, so that enzyme expression peaks in the morning to support biosynthesis later on when mid-day sunlight intensity demands high ascorbic acid concentrations. Minor pathways may be specific to certain parts of plants; these can be either identical to the vertebrate pathway