Expensive skin creams rich in antioxidants and championed by the beauty industry for anti-ageing and wrinkle-reducing effects could actually harm the skin of younger people, according to a study.
Antioxidants were thought to be beneficial as they stop free radicals damaging cells. However research suggests that in people under 50 free radicals are essential for skin healing and healthy regeneration.
When scientists in the US bred mice with excess free radicals to mirror the effects in humans, they expected to see accelerated ageing - but instead they found the animals' skin improved.
Prof Judith Campisi, of California's Buck Institute for Research on Ageing, said "This study shows that it's essential that we look across the entire lifespan when we examine mechanisms implicated in the ageing process.
"We found unexpected effects; mechanisms that benefit us when we're young, cause problems as we age."
Prof Campisi said eating, or applying large amounts of, antioxidants might damage skin in young people as free radicals are needed to keep skin regenerating effectively.
Beta-carotene and vitamins C and E have high levels of antioxidants and many people take supplements to try and slow ageing.
Dr Michael Velarde, lead author of the study, said: "This is not a simple process. It may be that nature used free radicals to optimize skin health, but because this process is not deleterious to the organism until later in life, past its reproductive age, there was no need to evolve ways to alter this mechanism."
Free radicals are atoms with electrons missing, which take them from other healthy atoms, damaging cells via oxidation. Antioxidants essentially 'donate' electrons to neutralise free radicals and stop the harm.
Free radicals are produced as a by-product of normal metabolism and can also be introduced from an outside source, such as tobacco smoke, or other toxins including pollution.
Health experts and beauticians have long recommended eating superfoods such as blueberries and using formulated creams to boost antioxidants and fight free radicals.
However it appears they may work only in older age: as the study mice aged, their skin cells became increasingly damaged by free radicals, eventually stopping dividing completely.
The research follows controversial claims by Dr James Watson, co-discoverer of the structure of DNA, that antioxidants may be harmful to people with late-stage cancer.
He said free radicals help clear dysfunctional and dangerous cells; antioxidants may hinder cancer recovery by blocking their effect, he said.
The research was published in the journal Proceedings of the National Academy of Sciences.