Mostly Antioxidants are peacemakers in the molecular war. But the work they do is not always good work.under some circumstances-and this is not well understood-antioxidants can turn into pro-oxidants and promote free radical formation. For example, studies have found that beta carotene, an antioxidant, can increase the risk of lung cancers in smokers apparently because it turns into a pro-oxidant. Moreover low doses quench them.
For this reason, people under treatment for cancer are often advised not to take vatamin C or other antioxidant supplements, which may actually interfere with radiation and chemotherapy, rather than provide benefits.