When the idea of a possible link between deodorant and breast cancer surfaced a decade ago, it seemed about as likely as the ''underwire bras cause cancer'' myth. How could deodorant inflict anything nastier than a brief sting in the armpit if you'd nicked yourself shaving?
One of the scientists who drew attention to a possible cancer connection was Dr Philippa Darbre, of the school of biological sciences at Britain's University of Reading. When she found traces of preservatives commonly used in cosmetics and toiletries in samples of tissue from human breast tumours, she had no way of knowing where these chemicals - called parabens - had come from.
After all, parabens are widely used in many personal care products, including shampoos, hand-washing gels, moisturisers and sunscreens - not just deodorant.
But her concern was that not only could these chemicals be absorbed through the skin, but in animal studies they had been found to mimic the action of oestrogen. Could it be that parabens in products applied on or close to the breast contribute to breast cancer, a hormone-related disease?
Ten years on, we still don't know the answer, but Darbre is still plugging away trying to learn more about how parabens and other chemicals behave in breast tissue. Her latest research, published this year in the Journal of Applied Toxicology, found that in lab studies parabens could make breast cancer cells grow. The levels of parabens she used in this study were the same as those she had detected earlier in samples of human breast tissue.
Should we be worried? Not at the moment, according to Cancer Australia executive chief Dr Helen Zorbas, who says there is no strong evidence linking parabens to an increased risk of breast cancer.
''With breast cancer, there's research on many different fronts and while there are many theories and plausible risk factors, we need quality evidence to make recommendations,'' she says. ''With parabens, there's no evidence of causality and we need more and better studies before we change our advice.''
It's also important not to focus on unproven links to breast cancer while turning a blind eye to other well-known and avoidable risk factors, she says. Being overweight after menopause is one of these factors, while alcohol is another.
''On average, each standard drink a woman has in a day increases her risk of breast cancer by 7 per cent compared with women who don't drink,'' Zorbas says.
But while most of the concern about parabens has focused on their possible effects on breasts, emerging research suggests they might affect sperm, too. A 2010 study of men attending a US fertility clinic found a link between levels of parabens and DNA damage - although it's early days and more studies need to be done. Still, some companies have withdrawn parabens from their products and ''paraben-free'' is now appearing on many packages.
In 2011, Denmark prohibited their use in personal care products for children under three, says Dr Mariann Lloyd-Smith, senior adviser to the community environmental organisation the National Toxics Network.
But, as she points out, parabens are just one of many chemicals in our environment that come under the heading of ''endocrine disruptors'', meaning they're capable of affecting our hormones.
''Most of these chemicals have never been assessed,'' Lloyd-Smith says. ''You have governments still struggling to understand the effects of single chemicals - so how can we know what the effect of a mixture of these chemicals might be on human health?
''Even if the oestrogenic effect of parabens is mild, you'd think that would be enough to say, 'Why take this risk when you can make cosmetics without them?'''
Lloyd-Smith isn't a lone voice. In February, the World Health Organisation released a report, State of the Science of Endocrine Disrupting Chemicals, which didn't mince words on the subject of potential harm from endocrine disruptors.
Rates of hormone-related cancers, including breast, ovarian, testicular, endometrial and prostate cancer, have risen worldwide over the past 50 years, yet of the almost 800 chemicals known to be capable of interfering with human hormones, or suspected of doing so, only a small fraction has been investigated, the report says.
Because of this gap in our knowledge, Darbre is looking beyond parabens to the effects of other environmental chemicals on breast tissue.
''Although I'm concerned about the oestrogenic properties of parabens, they're not the only oestrogenic chemicals that have been measured in the human breast,'' she says.
''This doesn't make parabens any less important, but it's like a jigsaw - while each piece of the puzzle is significant, it takes more than one piece to create a picture.''
If you'd rather not wait for science to figure all this out, how can you reduce your exposure to parabens? Read the fine print on the label. While some cosmetics and personal care products declare they're paraben-free, with others you'll need to scan the ingredients to check whether parabens are listed.
That's not always straightforward. While these chemicals often have ''paraben'' in their name, such as methylparaben and propylparaben, they're also known by other names such as benzoic acid and benzoate.
For a complete list (and it's a long one), see the fact sheet on parabens on the website of the National Industrial Chemicals Notification and Assessment Scheme (NICNAS) at nicnas.gov.au. For the record, NICNAS believes that ''further research is required before a causal link between parabens in cosmetic products and breast cancer can be established''.
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