The survey, of more than a million women revealed these inexplicable patterns, also implicating systems analysts, beauticians and telephone operators as having a higher than normal risk.

Writing in the American Journal of Public Health, Dr Marina Pollan and Dr Per Gustavsson said that some of the statistical blips might be due to the career paths followed by white collar workers.

Having children later increases risk

Some might be having children later - an established risk factor - and be checked more often for breast cancer.

Hairdressers are more likely to fall prey to breast cancer

They wrote: "while the high risks observed among professional, administrative and clerical workers might be related to lower birth rates and increased case detection, excess risks for telephone workers and for hairdressers and beauticians deserve further attention."

Dr Gaby Tobias, A GP in East London who helped write guidelines for managing breast disease, said that later pregnancy was a well-established risk.

"It is not as signifiacant risk as having a family history of the disease, but it thought to be one of the reasons why the disease is on the increase," she said.

The study's authors speculated that exposure to chemicals used in the hair and beauty industry might contribute to the extra risk.

Currently, one in 12 British women, and one in eight US women will get the disease at some point in their lives.

Other well known risk factors are age, obesity and taking hormone replacement therapy.

However, in the Swedish study, this could only explain just over half the breast cancer cases recorded.

Alternative therapies could mean depression

A separate study published the New England Journal of Medicine has found that women who turn to alternative therapies shortly after surgery for breast cancer may be suffering from depression or anxiety.

Acupuncture following breast surgery could be a sign of depression

Researchers asked 480 US women diagnosed with early-stage breast cancer about their use of alternative therapies - and found that 28 per cent had done so following surgery.

The treatments used included acupuncture, herbal medicines, vitamins and homeopathy, and the women who used them were found to be generally younger and well-educated. Those who did told of greater feelings of depression, and fear of recurrance.