The mechanism that produces white hair is not well known. It is very likely, although not definitely proven, due to the oxidation of melanin caused by the aging of the hair follicle cells. A recent theory suggests that follicles age and begin to produce an oxidant that damages the melanin. The hair then loses colour and turns white due to the loss of this property.
It has not yet been possible to prove that any antioxidant cream will prevent hair from turning white. This is because the product would have to be applied for a lifetime, since once they lose colour, the cells no longer contain melanin.
José Viña is the Full Professor of Physiology of the University of Valencia and an expert on aging and related treatments.