What should an ideal antioxidant do (and not do)?

Superoxide, H2O2 and particularly activated hydroxyl radicals (OH.) can cause lipid peroxidation, destroy enzymes and anti-elastases, produce DNA breaks and lead to death of mammalian cells. Conversely, these active oxygen species may also be very important for the killing of some microbial infective agents. Clearly the therapeutic potential for reducing the destructive activity of oxidants must be offset by any harm which may result from inhibition of these protective actions of oxidants. The challenge lies in providing the one without the other.