Exposure to relatively small amounts of parabens, phthalates and triclosan, chemicals commonly found in personal care products, are suspected of contributing to breast cancer risk. For example, parabens have been shown to be xenoestrogens, man-made compounds that activate estrogen receptors, thereby increasing ER+ risk.
Note that these classes of chemicals are absorbed into circulation through the skin. In other words, they can penetrate human skin intact and be absorbed systemically. A variety of sunscreen compounds have long been suspected of increasing cancer risk. Now a new study has reported that six compounds found in some sunscreens and other UVF-rated products can increase the migration and invasion of both ER+ and estrogen receptor negative (ER-) breast cancer cells.

Latest research finds sunscreen compounds increase metastasis

The study referenced above was designed to investigate the potential of benzophenone (BP)-1, BP-2, BP-3, octylmethoxycinnamate (OMC), 4-methylbenzilidenecamphor and homosalate to influence breast cancer metastasis. In particular, the authors examined the effects of these compounds on migration and invasion of breast cancer cells. These compounds are added to personal care products to act as sunscreens by absorbing ultraviolet light. The fact that they are present in human milk and their demonstrated estrogenic activity suggest they could play a role in breast cancer development.
In the study, long-term exposure (more than 20 weeks) to each of the six compounds was found to increase the motility (the ability to move, which is required for metastasis) of ER+/PR+ MCF-7 breast cancer cells using three independent assay systems. Such exposure also increased invasive activity. Increased motility of triple negative MDA-MB-231 breast cancer cells was also observed after 15 weeks of exposure to each of the six compounds.
These results imply that the heightened migratory activity was not restricted to estrogen-responsive cells. In fact, the molecular mechanisms varied between compounds and cell lines. The authors conclude that exposure to any of these six compounds can increase migration and invasion of breast cancer cells.
Please see our article on phthalates and the personal care products tag for more information.