Women who have dyed their hair or use hormonal contraception are at risk of breast cancer, scientists warn.
Changing the colour of locks has previously been linked to the disease, but a new study backs up the evidence.
Being exposed to carcinogenics in the dyes was linked to a 23 per cent chance of getting breast cancer.
Users of birth control methods such as the combined Pill and IUS coils could also face the same plight.
Post-menopausal women fitted with the latter have a 52 per cent greater chance of developing breast cancer.
And there is a 32 per cent increased risk for those who use the former hormonal-based contraceptive, Finnish researchers claim.
The findings add to the growing body of evidence that progesterone-based birth control methods are a risk factor of breast cancer.
They are listed by Cancer Research UK alongside alcohol and being fat in the causes with ‘sufficient’ evidence to the disease.
Having high levels of the body’s own natural hormones also increases the risk of ovarian cancer and blood clots.
Research has shown certain ones such as oestrogen cause DNA mutations, leaving cells prone to turning cancerous. Progesterone is also known to fuel the growth of tumours.
Both can be found in the combined Pill, but only a synthetic version of the latter exists in IUS coils.
The T-shaped devices work by releasing the hormone into the womb, thickening the mucus in cervix.
This in turn makes it more difficult for sperm to swim through and access the egg.
And previous studies have shown that women who regularly dye their hair are at risk of bladder, brain cancer and leukaemia.
British scientists once warned that the hair colouring kits used both at home and expensive salons pose a potential health risk.
It is believed that chemicals in permanent hair dyes react with other pollutants in the air to form tumours.
It is estimated that slightly more than a third of women regularly colour their hair, while much less use the IUS devices.
Experts from the University of Helsinki used survey data from around 8,000 breast cancer patients.
They were asked whether they had hormonal contraceptives or if they had ever dyed their hair.
The scientists then assessed to see whether or not there was a link between both factors and the risk of breast cancer.
However, the researchers say more research is needed on both items to truly assess their risk of breast cancer.
Dr Jasmine Just, Cancer Research UK’s health information officer, said: ‘There’s no convincing evidence that women who use hair dyes are at an increased risk of breast cancer.
‘But, there is clear evidence that the risk of breast cancer can be reduced through things like keeping a healthy weight, being more active and cutting down on alcohol.’