The Way We Live: Sunbathing is twice as dangerous as we thought

At the present rate of increase, non-Hodgkin's lymphoma is set to become the third or fourth most common cancer by 2010. An atlas displaying the geographical distribution of leukaemias and other blood cancers, published yesterday, shows that cases have risen 40 per cent in the last decade.

The cause of the rise has baffled scientists but it has paralleled the increase in melanoma. There are 4,000 new cases of melanoma a year and 5,000 new cases of non-Hodgkin's lymphoma. Both diseases are commoner in the sunnier counties of Cornwall, Devon and Somerset than in the north. The same pattern is seen in Europe, America and Australia.

Increasing affluence and the trend to take holidays in the sun are believed to be behind the rise in both cancers. The effects of global warming and thinning of the ozone layer are expected to increase the incidence of cancers caused by sunlight by10 per cent over the next 50 years.

Professor Ray Cartwright, director of the Leukaemia Research Fund centre for clinical epidemiology at Leeds University, said: "Increasing exposure to sunlight is my favourite hypothesis for the rise in non-Hodgkin's lymphoma. People who get skin cancer also get more lymphomas. Farmers who are out in the sun more get more of both diseases. Darker skinned people are protected against them."

"We know from work on sunbeds that exposure to them takes away some of the immune properties of the white blood cells. It is still a hypothesis but if it is true it means there are simple public health measures we can take, such as telling people to cover up in the sun."

Professor Cartwright said other explanations were increasing pollution from cars, which would be much harder to control, and changing use of antibiotics over the past 50 years which may have affected people's immunity and changed the nature of the infections to which they are exposed.

The first sign of lymphoma, which is a cancer of the lymph glands, is a lump in the neck, armpit or groin. At a later stage the cancer affects the liver, spleen and bone marrow and ultimately causes bone marrow failure when it ceases to produce new blood cells. Treatment is by radiotherapy and chemotherapy and 70 per cent of patients survive five years.

The atlas and handbook giving guidance on the investigation of leukaemia "clusters", published by the Leukaemia Research Fund, provide the most comprehensive picture of all that is known about one of the most feared cancers. It focuses on two areas, the North and the South-west, and is based on 27,000 cases of the diseases from 1984-93.

Leukaemia is perceived to be a disease of childhood because one type, acute lymphoblastic leukaemia, peaks in the under-20s and there are fears that it may be linked with exposure to radiation from nuclear power stations or overhead electricity cables. In fact, there is little evidence of either link and leukaemia affects ten times more adults than children.

Dr David Grant, scientific director of the fund, said the failure to pinpoint the causes of leukaemia was "one of the most distressing unanswered questions" for patients and their families which the atlas would help tackle. The answer was likely to be a combination of genetic, environmental, lifestyle and occupational factors. "The pattern of the diseases over the country, the differences between the sexes - blood cancers are more common in men, especially after age 50 - and between age groups, could provide clues to their causes," he said.

In some blood cancers, such as Hodgkin's disease, there was likely to be an infectious cause.