Why rats shouldn’t wear lipstick

“Could lipstick give you breast cancer?”, the Daily Mail asked today. The newspaper reported a warning from scientists that chemicals found in lipstick and nail varnish could trigger breast cancer. The paper goes on to explain that the chemical, butyl benzyl phthalate (BBP) is one of a group of chemicals called phthalates which are used to soften plastics. The chemical can be found in a range of products including food packaging, toys, carpets and solvents, where it is used to make the products “glossy”.

The scientists have warned that this man-made substance could mimic the female sex hormone oestrogen and by accumulating in fat cells could trigger breast cancer or lead to early puberty in girls.

The study, carried out in rats, indicates that BBP can interfere with the healthy development of breast tissue. Although not directly applicable to humans, this study does indicate a need for further studies into this chemical and alternatives to its use.

Adding BBP to cosmetics - including lipstick - is already prohibited in the EU. The response to the Daily Mail article from The Cosmetic, Toiletry & Perfumery Association (CTPA) can be found at their website.

Where did the story come from?

Dr Raquel Moral and colleagues from the Breast Cancer Research Laboratory, Fox Chase Cancer Center, Philadelphia, carried out this research. The study was supported by a grant from the National Institute of Environmental Health Sciences and the National Cancer Institute in the US.

The study was published as an open access provisional document on BioMed Central for the (peer-reviewed) medical journal: BMC Genomics .

What kind of scientific study was this?

In this experimental animal study, the researchers investigated the affects of BBP exposure in newborn rats as they matured and developed breast tissue.

They say that research has shown that the chemical BBP is an endocrine disrupter, having adverse effects on the male reproductive system and mimicking the action of the female hormone oestrogen. A previous study found harmful effects from prenatal exposure to this chemical in humans and the European Commission has restricted its use in plastic toys and childcare products.

As the chemical is commonly used in pipes, floor tiles and carpet backing, as well as in cosmetics, the researchers wanted to demonstrate the endocrine disrupting effect by examining the shape and development of breast tissue in young rats.

The rat pups were born in litters of 10 and from day two to day 20 all the pups were fed a mixture of BBP and sesame oil. The rats were weaned at 21 days and then fed a pre-prepared, hormone-free diet without any BBP.

In order to measure the rats’ mammary glands at different ages of development, the researchers formed four groups of female offspring with more than 27 rats in each group. At 21, 35, 50 and 100 days, one of the groups was given a microscopic examination that looked for cellular changes and what the researchers called the “genomic signature” of the rat mammary gland. At 21 days, that group was also measured for their degree of maturity.

The researchers extracted the RNA, the substance in cells that carries instructions from DNA to create proteins, from the mammary glands of the rats and determined to which gene, out of several hundred, this RNA belonged. They tested these genes as to whether they were “up-regulated”: the researchers state that this is a predictor of causing cancer.

What were the results of the study?

The researchers report that exposure to BBP increased the rats’ uterine weight/body weight ratio at 21 days. BBP did not produce significant changes to the shape or size of the mammary gland.

The main finding was that BBP did make changes to the genes of the mammary gland at the end of the 21 day exposure period. At this point, a significant number of genes (515) related to growth and development of the mammary glands, were up-regulated in the exposed animals, indicating a propensity to develop cancer.

What interpretations did the researchers draw from these results?

The researchers interpret these results as suggesting that BBP has a short-term effect in increasing relative uterine weight, but also that it has an effect on the genes of the mammary gland of rats at 21 days.

They comment that they are unable to rule out long-term changes and say that to get the “full relevance of these findings” further animal studies are required where cancer actually develops.

What does the NHS Knowledge Service make of this study?

This is an important study as it shows that the genetic profile of rats can be changed by their exposure to the common chemical, butyl benzyl phthalate. Further research is needed to investigate if the changes (up-regulation) to genes shown at an early stage (21 days) in rat mammary glands persist long-term and if the changes are actually linked to breast cancer in rats.

It will also need to be established if the exposure to this substance produces any kind of similar change at a cellular level in humans. The typical level of exposure that humans, and particularly children, have to this chemical will also need to be investigated and the question answered if there is a safe level of human exposure. It also needs to be known if there are there other phthalates in common use which have similar effects.

The authors of this study describe ongoing research aimed at providing answers to these and other questions. As such, more reports about BBP will probably appear in the future.

Sir Muir Gray adds…

The message is simple: try to use as few chemicals as possible for as short a time as possible.