Analysis of 20 breast tumours found high concentrations of para-hydroxybenzoic acids (parabens) in 18 samples. Parabens can mimic the hormone estrogen, which is known to play a role in the development of breast cancers. The preservatives are used in many cosmetics and some foods to increase their shelf-life.

"From this research it is not possible to say whether parabens actually caused these tumours, but they may certainly be associated with the overall rise in breast cancer cases," says Philip Harvey, an editor of the Journal of Applied Toxicology, which published the research.

"Given that breast cancer is the largest killer of women and a very high percentage of young women use underarm deodorants, I think we should be carrying out properly funded, further investigations into parabens and where they are found in the body," Harvey told New Scientist.

The new research was led by molecular biologist Philippa Darbre, at the University of Reading. She says that the ester-bearing form of parabens found in the tumours indicates it came from something applied to the skin, such as an underarm deodorant, cream or body spray. When parabens are eaten, they are metabolised and lose the ester group, making them less strongly estrogen-mimicking.

"One would expect tumours to occur evenly, with 20 per cent arising in each of the five areas of the breast," Darbre told New Scientist. "But these results help explain why up to 60 per cent of all breast tumours are found in just one-fifth of the breast - the upper-outer quadrant, nearest the underarm."

However, Chris Flower, director general of the Cosmetic, Toiletry and Perfumery Association, challenged the study's findings. "There are almost no deodorants and body sprays that contain parabens," he says. "Although they are in most other creams and cosmetics, the safety margin is huge and they would not have any effect on enhancing growth of new tumours."

Darbre replies that deodorants and antiperspirants have only stopped containing parabens in the last few months and that the tumours she studied occurred prior to this.

A small survey by New Scientist of three British high street shops and one supermarket found deodorants in each that contained parabens, although most of these products did not. However, many other products used under the arm commonly contained parabens, such as body sprays, hair removal creams and shaving gels. Body lotions, face creams, cleansers and shampoos also frequently contained parabens.

Previously published studies have shown that parabens are able to be absorbed through the skin and to bind to the body's estrogen-receptors, where they can encourage breast cancer cell growth.

But Flower maintains that the amount of parabens absorbed by the skin is very low and the parabens are "metabolised by the skin cells to produce products that have no estrogenic activity".

Darbre's research did not look at the concentrations of parabens in other areas of the breast or body tissues and Harvey cautions that the significance of the chemicals in tumour tissue should not be over-interpreted.

Darbre says she has not used cosmetic products, including underarm deodorants, for eight years. She recommends that other women do the same "until their safety can be established".