Chemicals found in lipstick and nail varnish could trigger breast cancer, scientists warned yesterday.
A study has shown that butyl benzyl phthalate, or BBP, can interfere with the healthy development of breast tissue.
Environmental campaigners yesterday called for it to be banned in the cosmetic industry, where it is used to make products glossy.
The man-made substance is part of the phthalate family of chemicals, which mimic the female sex hormone oestrogen.
Phthalates are widely used to soften plastics and are found in food packaging, toys, carpets and solvents.
Past studies have linked them to birth defects, kidney problems and infertility.
They have been banned in teething rings and babies' dummies across Europe.
Now, scientists at the Fox Chase Cancer Centre in Philadelphia say that BBP - which accumulates in our fat cells - could increase the risks of breast cancer.
The team fed lactating rats with BBP, which was then absorbed by their offspring via breast milk.
The baby rats were exposed to levels of the chemical estimated to be nearly equivalent to the American Environmental Protection Agency's safe dose for humans, the researchers reported in the online journal BMC Genomics.
The chemical altered the genetic make-up of cells in the young female rat's mammary glands.
Although the effects wore off once BBP was removed from the diet, the subtle changes could have an effect later in life, the scientists say.
"We are the first to report that neonatal/prepubertal exposure to BBP induced modifications in the gene expression of the mammary tissue," said team leader Dr Jose Russo.
"BBP is in the environment, so a constant exposure via inhalation and digestive tract can reach many different organs including the breast.
"In this study, we found how the action of this compound present in everyday life affects the development of the rats.
"This is an indication that the same could happen in humans. Even if an individual is exposed to it in the beginning of life, BBP can cause alterations later in life.
"In this direction, we are evaluating if the exposure of this compound in young girls is associated with early puberty and breast development."
The researchers say more studies are needed to determine if the chemical actually does increase the risk of breast cancer in rats.
Two years ago a study found one of the first links between phthalates and genital defects.
Researchers at the University of Rochester, New York, discovered that women with higher levels of phthalate break-down chemicals, or metabolites, in their urine were more likely to give birth to boys with under-developed sexual organs.
The Women's Environmental Network said phthalates were present in four out of five cosmetic products on sale in Britain.
"There are safer alternatives," said a spokesman. "We want to see them removed from all cosmetics. People are putting numerous cosmetics on their skin each day - from shower gel, to hair spray and moisturiser.
"Trace elements are being absorbed by the skin and they can build up in the body and have a long-term effect."