Parabens are widely used in shampoos, cosmetics and body lotions and sunscreens and have been previously associated with cancer as they activate the production of oestrogen, mimicking the natural hormone oestradiol.
Both oestradiol and oestrogens have been linked to breast cancer and reproductive problems.
“Although parabens are known to mimic the growth effects of oestrogens on breast cancer cells, some consider their effect too weak to cause harm,” said lead investigator Dale Leitman, a gynaecologist and molecular biologist at University of California Berkeley.
“But this might not be true when parabens are combined with other agents that regulate cell growth.”
Safety tests which measure the effects that chemicals have on humans currently only monitor parabens in isolation, according to the study published in the Environmental Health Perspectives journal.
They do not look at whether parabens could interact with other molecules and together increase the risk of breast cancer.
Scientists are keen to explore whether exposure to these chemicals during times of development such as puberty and pregnancy could increase their risk of breast cancer later in life.