Phthalates are chemicals used primarily as plasticizers of polyvinyl chloride. Plasticizers impart flexibility and resilience to plastics. Phthalates also are used as solubilizing or stabilizing agents in some personal care products. Food packaging and lotions and creams are the main sources of phthalate exposure for most people.
Using certain prescription drugs and vaginal douches can also increase phthalate levels. Phthalates are metabolized and eliminated quickly and do not accumulate in the body.
Phthalates have estrogenic effects but can also induce proliferation and invasiveness of hormone receptor negative breast cancer cells. Women with breast cancer had higher levels of monoethyl phthalate (MEP) than cancer-free women in one study. Prenatal exposure of rodents to relatively high levels of phthalates has been reported to result in (1) demasculinizing effects in male offspring; (2) abnormal mammary cell growth in females; and (3) increased susceptibility to carcinogen-induced mammary tumor development in females. While more studies are needed to clarify the association between typical phthalate levels and breast cancer, taking steps to reduce exposure makes sense.
Food packaging and personal care products are main sources
Exposure to phthalate is widespread; most of the people who have been tested in a variety of Western and Asian countries have been found to have phthalate metabolites in their urine.
Phthalates such as diethyl phthalate (DEP) and dibutyl phthalate (DBP), which are used in lotions and creams, can be absorbed through the skin. One study that investigated urinary levels of metabolites of DEP and DBP after topical application reported that 5.79% of the applied DEP and 1.82% of the DBP, on average, could be recovered in urine as MEP and monobutyl phthalate (MBP). The concentration of the compounds peaked in the urine within eight to 12 hours after the cream was applied. In other words, DEP and DBP are absorbed into circulation and metabolized following application on the skin.
Bis(2-ethylhexyl) phthalate (DEHP) (which makes plastics more pliable) is widely used in plastics and resins for food packaging, along with bisphenol A (BPA). Phthalates and BPA have both been reported to leach into coffee from single-serve coffee pods.
A study that was designed to estimate the contribution of food packaging to phthalate and BPA exposure measured metabolites in the urine of study participants before, during and after a non-packaged foods dietary intervention. Participants ate their usual diet, then for three days consumed only fresh foods (not canned or packaged in plastic and no restaurant meals), after which they returned to their normal diet. Consuming fresh food only reduced the levels of DEHP and its metabolites by 53% to 56% and BPA levels by 66%, on average. Maximum DEHP metabolite levels were reduced by 93% to 96%. In other words, DEHP and BPA exposures can be reduced substantially by consuming only foods with limited packaging.
Phthalates induce proliferation and invasiveness of TN cells
Since phthalates are endocrine disruptors with estrogenic effects, most studies have focused on hormone receptor positive (ER+) breast cancer. However, one study that examined the influence of two phthalates, n-butyl benzyl phthalate (also known as benzyl butyl phthalate) (BBP) and DBP, in triple negative (ER-/PR-/HER2-) breast cancer cells, reported that the treatments induced proliferation, migration, invasion, and tumor formation. The authors uncovered a cancer-promoting mechanism by which phthalates promoted breast cancer independent of their estrogenic activities.
Prenatal exposure may increase breast cancer risk in adulthood
Exposure to phthalates has been shown to cause a variety of unfavorable reproductive outcomes in animal studies. Most studies have focused on male reproductive health. Prenatal exposure to high doses of phthalates can result in demasculinizing effects in male rat pups as a result of impaired testosterone production by fetal testes.
However, one study has examined the impact of prenatal exposure to very high doses of mono-2-ethylhexylphthalate (MEHP) on the female offspring of exposed mice. MEHP was found to have a variety of influences on the female reproductive system and the mice had high rates of abnormal cell growth in mammary glands in adulthood. In addition, another study reported that girls significantly exposed to phthalates while in the womb were more likely to experience early puberty than those not so exposed.
Phthalate exposure linked to early puberty
A 2021 Korean study reported that girls with high concentrations of phthalates had a significantly increased risk of early menarche compared to those with the lowest concentration. Early age at puberty is a known risk factor for breast cancer.
Women with breast cancer have higher phthalate levels
While cell and animal studies show that phthalates lead to changes that could induce or promote breast cancer, very few studies have attempted to link phthalate exposure to similar effects in women. In one study, the authors examined the associations between urinary concentrations of nine phthalate metabolites and breast cancer in women residing in northern Mexico.
Concentrations of MEP were found to be higher in women with breast cancer than cancer-free women, whereas controls had significantly higher concentrations of mono-n-butyl phthalate (mBP), mono(2-ethyl-5-oxohexyl) phthalate (MEHHP), and mono(3-carboxypropyl) phthalate (MCPP) than cases. Women in the highest third of MEP levels were found to have more than twice the risk of breast cancer as women in the lowest third, after adjusting for breast cancer risk factors and other phthalates. This association was stronger among premenopausal women, in whom those in the highest exposure level had four times the risk. Cancer-free women had significantly higher concentrations of three phthalates (mBP, MEHHP, MCPP) than did the breast cancer cases and high levels of monobenzyl phthalate (MBzP) and MCPP were associated with lower risk of breast cancer.
Phthalates may interfere with BC treatment
BBP has been shown to increase resistance to Adriamycin (doxorubicin) plus cyclophosphamide chemotherapy regimens. The same study found that BBP also increased angiogenesis in a mouse model of breast cancer. BBP is used in making vinyl floor tiles, carpet backing, car trims and dashboards, as well as artificial leather. It is also added to some adhesives, perfumes, and hair sprays.
Taking steps to reduce phthalate exposure makes sense
Under current Environmental Protection Agency (EPA) guidelines, average exposures among U.S. consumers are below unsafe levels. However, the EPA has announced that it is in the process of developing a set of principles for evaluating cumulative risks posed by certain phthalate chemicals under the Toxic Substances Control Act (TSCA). Note that European regulations are stricter with regard to potential phthalate exposure and consumers there appear to enjoy a higher level of protection.
Although most research concerning phthalates has produced concerning results, many of the studies have been conducted at relatively high doses to which human beings would normally not be exposed. On the other hand, there is very little data on the effects of chronic phthalate exposure or the combination of phthalates with other endocrine disruptors or carcinogens. Avoiding phthalates (especially MEP) in personal care products and emphasizing fresh rather than packaged or restaurant foods are steps that can be taken to reduce exposure. In addition, some plastic containers are marked with a recycling number in a triangle-shaped icon. Plastics marked with the number 3 should be avoided since they incorporate polyvinyl chloride, which contains phthalates.
Below are links to 20 recent studies concerning this topic. For a more complete list of studies, please click on phthalates.