A diagnosis of breast cancer can be frightening, and many of the known risk factors – genetics, ageing, being a woman – are beyond our control. That is why myths are attractive. They sell us the idea that there is something simple we can do to protect ourselves from cancer. We look at three of the most common myths.

Your bra could be killing you

The idea that wearing an underwired bra can cause breast cancer has been around since 1995, when Sydney Singer and Soma Grismaijer published their book Dressed to Kill, which claimed there was a link. The idea was revived last year when a practitioner of alternative medicine wrote an essay on Gwyneth Paltrow’s website, Goop. What these people have in common is that none of them is a cancer researcher or medical doctor.

Singer and Grismaijer’s “study” was not reviewed by medical experts and published in a respected journal, as is the norm for bona fide scientific discoveries. According to a version of their story now doing the rounds on Twitter, they interviewed more than 4,000 American women and discovered that women who don’t wear bras have a “1 in 168 chance” of developing breast cancer, as opposed to a “3 in 4 chance for those who wear a bra 24 hours a day”.

Their explanation is that underwired bras block circulation of lymphatic fluid, causing breasts to swell with “toxins” (a word more associated with pseudoscience, in my experience, than genuine medical knowledge). It is unlikely, though, that that lymph fluid would be trapped by an underwire, because it doesn’t flow in that direction, and a properly fitting bra prevents breast ligaments from overstretching. Scientists have also criticised Dressed to Kill for not taking into account known risk factors for breast cancer, most notably obesity, which increases the likelihood a woman will wear a bra for longer periods.

A comprehensive 2014 study by the globally respected Fred Hutchinson Cancer Centre in Seattle found that no aspect of bra-wearing was associated with breast cancer risk, and Breast Cancer Now, Cancer Research UK, the American Cancer Society, and the US National Institutes of Health are just a few of the organisations that have stressed the lack of evidence that wearing bras increases cancer risk.

American obstetrician and gynae-cologist Dr Jennifer Gunter has described this myth as “cruel”, saying that it scares women and could cause women with a breast cancer diagnosis to blame themselves for wearing a bra. If you find your bra is painful, you should not panic that you have cancer, but you should head to the high street and get measured for a new bra.

Sweat-free armpits or healthy breasts? You have to choose

The idea that antiperspirants cause breast cancer is usually justified either by the idea that preventing underarm stickiness blocks “toxins” from being sweated out, or that the aluminium salts used to block the sweat glands are absorbed through the skin and trigger cancer. The source appears to be an email hoax which spread so quickly that cancer charity helplines were overwhelmed by anxious callers worried they had been doomed by their personal hygiene routines.

The vast majority of harmful substances in our bodies are flushed out by the liver and kidneys (which is why we drink lots of water when we are hungover), not sweated out through our armpits. Almost all the studies purporting to show that antiperspirants cause cancer are from a single laboratory, with Dr Philippa Darbre often the only named author. One of the studies that, at first glance, shows aluminium is present in breast tissue is, on a second look, inconclusive because the authors didn’t compare normal (non-cancerous) tissue. Unless there is significantly more of something in a tumour compared with normal tissue, it isn’t wise to speculate that it has a role in cancer.

A 2002 study published by the Journal of the National Cancer Institute studied 1,606 women and discovered there was no link between the use of antiperspirants and cancer. Another study, in 2006, compared women with and without breast cancer and found that 82% of women who were cancer-free had used antiperspirant whereas only 52% of the women with breast cancer had, which certainly doesn’t support the theory that antiperspirants increase cancer risk.

Mammograms emit cancer-causing radiation, or squeeze tumours so the cancer spreads

Finding breast cancer early reduces your risk of dying from it by up to 25% – which makes the myth that mammograms cause cancer, or make it spread, a particularly dangerous one. The consensus in the medical community is that the benefits of mammograms far outweigh any risk. An annual, 20-minute mammogram involves a tiny dose of radiation, less than a chest X-ray and nowhere near enough to increase the risk of developing a cancer. The process of metastasis, in which cells break off a tumour, spread, and settle in a different place in the body to create a secondary tumour, is biologically complex and can’t be caused by squeezing a tumour. Mammograms are frightening because of the potential that they will find a cancer – but the mantra that early detection saves lives is true and one of the reasons that what used to be a death sentence is now survived by eight out of every 10 women diagnosed with breast cancer.

If you are worried about cancer, you can find reliable information from NHS Choices, or the websites and helpline of registered cancer charities such as Cancer Research UK, the Irish Cancer Society or Macmillan Cancer Support. As always, speak to your GP if you have any concerns about your health.

• Naomi Elster is a writer and scientist researching for a PhD in cancer medicine at the Royal College of Surgeons, Ireland, supported by the Irish Cancer Society