Dyeing your hair can increase the risks of developing breast cancer by nearly 25 per cent, according to new study.

And they discovered that using a contraceptive hormonal intrauterine system increases the risk of breast cancer in post menopausal women by more than half.

Hormonal IUDs have become increasingly popular as an alternative to the traditional coil, which uses copper to prevent pregnancy, because they reduce the discomfort of periods.

Researchers in Finland analysed data from 8,000 breast cancer sufferers and 20,000 other women.

The results show the use of hormonal intrauterine device was associated with 52% increased risk of breast cancer in post-menopausal women compared to women who had used copper intrauterine device.

Other hormonal contraceptives were associated with 32% higher breast cancer risk among younger women under 50 when compared to women who did not use hormonal contraceptives.

In her doctoral dissertation researcher Sanna Heikkinen, of the University of Helsinki and Finnish Cancer Registry, said: "There was also a 23% observed increase in the risk of breast cancer among women who dyed their hair compared to those who didn't."

But she added that further research was needed to confirm the roles of hormonal contraceptives - specifically hormonal intrauterine device - and hair dyes in breast cancer.

Dr Keikkinen added: "The biggest risk factor in breast cancer is high age, and known lifestyle-related risk factors include late age at first birth, small number of children, high alcohol consumption, and sedentary lifestyle."

Many of these factors have become significantly more common in Western countries, including Finland, during the last decades.

In her research, Heikkinen also warned of the dangers of unnecessary mammography which she discovered was very common.

More than 60% of people involved in the research reported having had a mammography before the screening age of 50.

She said: "Women should be more extensively informed of the harms of opportunistic mammography, such as accumulating radiation burden and the potential consequences of false positive or negative findings".