Risk factors in Alzheimer's disease.

Dangers of ozone depletion SIR,-The dangers of ozone depletion in the United Kingdom, particularly with regard to non- melanoma skin cancer, are probably much greater than estimated in the recent article on this topic by Fiona Godlee.'The figures given in the article suggest that non-melanoma skin cancer may rise by 8000 cases a year in Britain if there is a 10% reduction in total column ozone.This figure is based on current incidence figures from cancer registries,-which are widely accepted as being gross underestimates.2I recently suggested that the true incidence of non-melanoma skin cancer in England and Wales may be close to 100 000 cases a year.3If this is true then, using a formula devised at the National Cancer Institute, Bethesda, Maryland,4 we might expect something like 35 000 extra non-melanoma skin cancers each year in England and Wales.Furthermore, there would probably be a relative increase in the potentially more dangerous squamous cell carcinoma compared with basal cell carcinoma.'Of course, these figures should not be taken at their face value as it is difficult to give an exact percentage rise in skin cancers because predicting what changes may occur in holiday and clothing habits is impossible.6The article therefore highlights the inadequacy of registration of skin cancer in the United Kingdom.Few attempts have been made to define the extent of the problem, and thus monitoring adequately any changes that may occur in the incidence of skin cancer is going to be impossible.As I have pointed out previously, there is an urgent need to review and improve registration of skin cancer throughout the United Kingdom.