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2025
J Clin Oncol
A large California study of over 58,000 racially and ethnically diverse women found that long-term exposure to fine particulate matter (PM2.5) air pollution was associated with a statistically significant 28% increased risk of breast cancer for each 10 μg/m³ increase in PM2.5 concentration, with the association consistent across African American, Latino, and other ethnic groups. When combined with data from 10 other studies in a meta-analysis, PM2.5 exposure showed a borderline significant 5% increased breast cancer risk, providing strong evidence that air pollution is an important breast cancer risk factor. These findings emphasize that breast cancer prevention strategies should extend beyond individual lifestyle changes to include population-level policies aimed at reducing air pollution, particularly as traditional risk factors explain only half of breast cancer cases and incidence continues to rise globally.
2025
Environ Health Perspect
An updated analysis of the largest cohort of ethylene oxide (EtO)-exposed workers—7,549 women employed ≥1 year at 13 U.S. facilities followed from 1960-2021 (181 breast cancer deaths)—found that cumulative EtO exposure was strongly associated with elevated breast cancer mortality, with workers accruing 3,650 ppm-days of exposure (equivalent to 10 years at 1 ppm) having over three times the breast cancer death rate compared to unexposed workers (RR = 3.15; 95% CI: 1.78-5.60) using a 20-year lag model. This association remained robust in a subcohort with interview data on breast cancer risk factors after matching on potential confounders (RR = 3.22; 95% CI: 1.52-7.13), with evidence of variation by time since exposure and exposure rate. These findings provide strong evidence that EtO is a human breast carcinogen and support recent emission reduction proposals, raising serious public health concerns given the high prevalence of breast cancer, large numbers of occupationally exposed workers, and potential for widespread environmental exposure from industrial facilities, with elevated risks observed even in low exposure ranges highlighting the need for stringent exposure controls and environmental monitoring.
2025
Ecotoxicol Environ Saf
This study analyzed six xenoestrogens (hormone-disrupting chemicals including phthalates, BPA, and alkylphenols) in atmospheric particles at a university campus in China from 2021 to 2023. BPA was the most prevalent xenoestrogen detected, with concentrations of these chemicals being significantly higher in winter than summer, and the overall cancer and non-cancer health risks were below threshold limits for the general population. However, infants and young children showed significantly higher risk values compared to other age groups, indicating they face greater health risks from atmospheric exposure to these endocrine disruptors. The research provides important data for developing policies to reduce health risks from airborne xenoestrogen exposure, particularly for vulnerable populations like children.
2024
Environ Health Perspect
A nationwide study using CDC biomonitoring data found that California’s Proposition 65, which requires warnings about chemicals that cause cancer or reproductive harm, led to reduced exposures to listed chemicals across the entire United States, not just California. While blood and urine concentrations of 37 monitored chemicals generally declined over time, the researchers found evidence of problematic chemical substitution—for example, after bisphenol A (BPA) was listed, its concentrations dropped 15% but levels of the unlisted substitute bisphenol S (BPS) increased 20%. Californians generally had lower levels of harmful chemicals in their bodies compared to residents of other states, suggesting the law had additional protective effects. The findings indicate that transparency laws like Prop 65 can drive manufacturers to reformulate products nationwide, but regulations need to address entire chemical classes rather than individual substances to prevent companies from simply switching to similar but unlisted toxic chemicals.
2024
Med Lav
A meta-analysis of 23 cohort and case-control studies found that occupational benzene exposure was associated with an 8% increased breast cancer risk overall, with high-level benzene exposure showing a stronger 35% increased risk. The association was consistent for cancer incidence (8% increased risk) though not statistically significant for cancer mortality, and significant heterogeneity was detected across studies based on sex, publication year, study design, quality, and industry of employment. These findings suggest that benzene—a recognized carcinogen primarily studied in relation to leukemia—may also increase breast cancer risk in occupationally exposed workers, though the authors acknowledge that bias, confounding factors, and publication bias limit the strength of causal inference, highlighting the need for high-quality prospective studies with detailed exposure assessment to confirm these associations and inform workplace safety standards for the millions of workers potentially exposed to benzene in petroleum, chemical manufacturing, automotive repair, and other industries.
2024
Environ Int
This large prospective study of over 170,000 women in the NIH-AARP Diet and Health Study examined whether air emissions of 19 known or suspected carcinogenic chemicals from industrial facilities (1987-1995) were associated with postmenopausal breast cancer risk through 2018. Women living within 1 km of high benzene emissions had more than double the breast cancer risk compared to unexposed women (HR=2.06, 95% CI: 1.34-3.17, p-trend=0.001), with the association weakening at greater distances and appearing strongest for invasive rather than ductal carcinoma in situ. Elevated risk was also observed for vinyl chloride exposure at 5 km distance (HR=1.20, 95% CI: 1.01-1.43, p-trend=0.04), with suggestive but unclear associations for asbestos, trichloroethylene, and styrene. These findings indicate that residential proximity to industrial facilities emitting benzene and other carcinogens may increase breast cancer risk, warranting further investigation particularly in diverse populations living near high concentrations of industrial sources.
2024
Int J Hyg Environ Health
A study of 48,665 California women in the Multiethnic Cohort found that exposure to specific ambient air toxics at residential addresses was associated with increased breast cancer risk over a 10-year follow-up period. Industrial chemicals showed the strongest associations, with 1,1,2,2-tetrachloroethane linked to a 322% increased risk, ethylene dichloride to a 181% increased risk, and vinyl chloride to a 127% increased risk. Gasoline-related pollutants also showed elevated risks, including benzene (32% increase), acrolein (126% increase), and toluene (29% increase), with generally stronger associations observed among African American and White women. These findings suggest that toxic air pollutants, particularly from industrial sources and vehicle emissions, may contribute to breast cancer development, which is especially concerning for populations living in high-pollution areas like Los Angeles.
2024
Cancer Epidemiol
A Canadian case-control study of 465 young women (ages 18-45) with breast cancer and 242 controls found that residential exposure to air pollution was strongly associated with increased breast cancer risk. For each interquartile range increase in nitrogen dioxide (NO₂) exposure—a traffic-related pollutant—women had a 133% increased risk of breast cancer at their current residence and a 116% increased risk based on exposure five years earlier. The findings suggest that traffic-related air pollution may be a particularly important and underrecognized breast cancer risk factor in younger women.
2023
Environ Res
A nationwide U.S. study of nearly 45,000 women found clear geographic patterns in breast cancer rates, with lower risk in the South and Southeast and higher risk in the Northwest and parts of the Midwest and Northeast, even after accounting for personal risk factors like family history and reproductive factors. Environmental exposures—including air pollution (nitrogen dioxide and fine particles), light at night, greenspace, and neighborhood socioeconomic disadvantage—explained 21% of the geographic variation in overall breast cancer and 63% of the variation specifically for estrogen receptor-positive (ER+) breast cancer. These findings provide strong evidence that where you live matters for breast cancer risk, with environmental factors playing a substantial role, particularly for ER+ breast cancer, the most common subtype, suggesting that reducing environmental exposures like air pollution and light at night could be effective prevention strategies at the community level.
2018
Discov Oncol
This systematic review examined the relation of 4 neighborhood factors on breast cancer incidence and prognosis among African-American women: neighborhood socioeconomic status (nSES), residential segregation, spatial access to mammography, and residential pollution. The authors found that nSES, residential segregation and access to mammography were all related to stage at diagnosis, and nSES and living in more segregated areas were both associated with mortality. Residential pollution was not associated with increased risk of breast cancer in the studies reviewed.
2000
Am J Indust Med
This Danish nationwide study of 230 male breast cancer cases found that men occupationally exposed to gasoline and its combustion products had a 2.5 times higher risk of breast cancer, with the risk rising to 5.4 times higher among men first exposed before age 40. Gasoline contains several known carcinogens including benzene and produces cancer-causing combustion products, which may explain this elevated risk. Since male breast cancer is rare but shares similar biology with female breast cancer, these findings suggest that gasoline exposure may also increase breast cancer risk in women and warrant further investigation in female workers.
2025
Epidemiol
A prospective study of 46,150 Sister Study participants followed for a median 13.4 years (4,155 breast cancer cases) used EPA Toxics Release Inventory data to quantify residential air emissions of 28 industrial compounds—many carcinogenic or endocrine-disrupting—during the 10 years before enrollment (2003-2006). Emissions within 3 km of residences showed non-significant associations with breast cancer for nickel compounds (HR = 1.3; 95% CI: 1.0-1.6 for highest vs. no exposure) and trichloroethylene (HR = 1.3; 95% CI: 1.0-1.6), while exposure continuum mapping identified 25 mixture profiles explaining 72% of emissions variance, with the joint-exposure response function suggesting higher breast cancer incidence among individuals with rare, high-emission profiles, though the overall mixture trend was not statistically significant (p = 0.09). These findings indicate that residential proximity to industrial air emissions of certain carcinogens—particularly nickel compounds and trichloroethylene—may be associated with increased breast cancer risk, though the lack of overall mixture association may reflect that individual compounds or specific emission sources are more important than cumulative exposure profiles, or that most participants experienced relatively low emissions with elevated risks concentrated among small subgroups with high exposure to specific pollutants.
2025
Sci Rep
A secondary analysis of 15,536 post-menopausal women from the Alberta Tomorrow Project cohort examined whether exposure to traffic-related air pollution (TRAP), measured using nitrogen dioxide (NO₂) levels, was associated with breast cancer risk over 12.6 years of follow-up during which 523 breast cancer cases were diagnosed. After adjusting for confounders including age, education, births, diet, income, physical activity, BMI, and smoking, the study found no significant association between NO₂ exposure and post-menopausal breast cancer risk (HR = 1.10 per 10-ppb increase in NO₂; 95% CI = 0.90, 1.34). The authors suggest that while the magnitude of risk observed was similar to other studies, the lack of statistical significance may be due to the study’s sample size limitations and the fact that NO₂ levels in Alberta are lower than in many other regions globally where associations have been found. These findings indicate that traffic-related air pollution may not significantly impact post-menopausal breast cancer risk in regions with relatively low pollution levels, though larger studies in more polluted areas may be needed to fully assess this relationship.
2024
Int J Environ Res Public Health
A systematic review of 25 epidemiological studies (2013-2022) found that seven out of eight investigated outdoor air pollutants showed significant associations with increased breast cancer risk, with benzo[a]pyrene showing the strongest relationship. The review found that 100% of studies examining nitrogen oxides (NOₓ), 83% of PM₂.₅ studies, 69% of nitrogen dioxide (NO₂) studies, and 43% of PM₁₀ studies demonstrated positive associations with breast cancer risk, with hazard ratios ranging from 1.05-1.56 and odds ratios from 1.03-1.86, while ozone and cadmium showed negative or no associations. These findings strengthen the evidence that outdoor air pollution—particularly traffic-related pollutants and fine particulate matter—contributes to breast cancer development, though the authors note that further research is needed to establish causal mechanisms, particularly through epigenetic pathways, and acknowledge that the review’s focus on English-language articles from developed countries may limit generalizability.
2024
Breast Cancer Res
A nested case-control study within the French E3N-Generations cohort examined 523 breast cancer cases and 523 matched controls to investigate whether thirteen metabolic health biomarkers mediate the relationship between exposure to three air pollutants (nitrogen dioxide, PCB153, and benzo[a]pyrene) and breast cancer risk. The study found that benzo[a]pyrene exposure was associated with a significant 2.32-fold increased breast cancer risk (highest vs. lowest quartile), PCB153 showed inconsistent positive associations, and nitrogen dioxide showed no association; among biomarkers, estradiol was associated with increased breast cancer risk (OR = 1.22 per SD). Four-way decomposition mediation analysis revealed suggestive evidence that albumin, HDL and LDL cholesterol, parathormone, and estradiol may partially mediate the associations between all three pollutants and breast cancer risk, though findings were limited by statistical power. These results provide preliminary mechanistic insights suggesting that air pollutants may influence breast cancer risk through alterations in metabolic biomarkers—particularly lipid metabolism and hormone regulation—though larger studies are needed to confirm these pathways and establish the clinical significance of these mediating effects in the relationship between environmental exposures and breast cancer development.
2023
Environ Res
A nationwide Danish study of 55,745 breast cancer cases matched with controls found that each 10 μg/m³ increase in fine particulate matter (PM₂.₅) air pollution exposure over 20 years was associated with a 21% increased breast cancer risk, with the association particularly strong (32% increased risk) among women diagnosed before age 55. While elemental carbon and nitrogen dioxide also showed modest associations initially, these disappeared in multi-pollutant models, suggesting PM₂.₅ is the primary air pollutant linked to breast cancer risk. These findings add breast cancer to the growing list of cancers associated with air pollution exposure and suggest that younger women may be especially vulnerable, though the authors caution that unmeasured confounding factors may influence the results.
2023
Cancer Epidemiol Biomark Prev
A pooled analysis of six European cohorts including 199,719 women followed for 3.6 million person-years found that long-term exposure to fine particulate matter (PM₂.₅) was associated with a 6% increased breast cancer risk per 5 μg/m³ increase. The association was strongest among middle-aged women (ages 50-54) and never-smokers, and notably, the cohorts studied represented the lower range of air pollution concentrations in Europe, suggesting that even relatively low levels of air pollution may contribute to breast cancer risk. These findings add to mounting evidence that air pollution—particularly fine particulate matter from traffic, industry, and combustion sources—is an environmental breast cancer risk factor operating independently of established risk factors, with important implications for public health policy, urban planning, and air quality regulations aimed at reducing population-level cancer burden, especially given that air pollution exposure is largely involuntary and affects entire populations.
2023
J Natl Cancer Inst
A large cohort study of 451,945 National Institutes of Health-AARP Diet and Health Study participants used EPA Toxics Release Inventory data to estimate historical environmental ethylene oxide (EtO) exposures based on proximity to EtO-emitting facilities, wind patterns, and emission levels from enrollment in 1995-1996. Among 173,670 postmenopausal women, living within 10 km of EtO facilities was associated with statistically significant breast cancer risk for invasive disease (HR = 1.03; 95% CI: 0.97-1.09); women in the highest quartile of the airborne emissions index showed elevated risk of in situ breast cancer at 10 km (HR = 1.25; 95% CI: 1.02-1.53), with no clear patterns for non-Hodgkin lymphoma risk. These findings reveal a novel potential association between environmental EtO exposure and in situ breast cancer—but not invasive breast cancer or lymphohematopoietic cancers—contrasting with occupational studies that found associations with invasive disease. The differential association with in situ versus invasive disease suggests EtO may influence early-stage breast carcinogenesis, though the mechanism remains unclear and warrants further investigation to understand why environmental exposures show different patterns than occupational exposures and why the effect appears limited to pre-invasive lesions.
2023
Environ Sci Technol
The following study discusses a strategic framework to improve how chemicals are managed in North America. The Essential-Use Approach is a policy that prioritizes restricting the use of chemicals based on necessity and safety. It proposes three guiding questions: Is the chemical essential to the product’s function? Is it the safest option? Is it necessary for health and safety? They also prioritize speed of assesments so that chemicals can be quickly phased out if evidence suggests danger to human health. This study is a call for change and aims to become a tool to simplify decision-making for regulating organizations, help businesses avoid liability related to harmful chemicals, and ultimately improve public health by ensuring only the safest substances are used in consumer products.
2022
Int Arch Occup Environ Health
A nationwide retrospective cohort study of over 4.7 million Taiwanese workers found that occupational exposure to specific hazardous chemicals was associated with significantly elevated breast cancer risk among female workers, with asbestos showing the highest increase (107% increased incidence, 80% increased risk after adjusting for age and exposure duration). Other notable associations included 1,1,2,2-tetrachloroethane (74% increased incidence, 52% adjusted risk increase), trichloroethylene/tetrachloroethylene (47% increased incidence, 42% adjusted risk increase), benzene (40% increased incidence, 38% adjusted risk increase), and lead (27% increased incidence, 31% adjusted risk increase), with associations remaining robust even after accounting for 2- or 5-year latency periods. These findings from 3,248 breast cancer cases among exposed workers provide compelling evidence that occupational chemical exposures substantially increase breast cancer risk, highlighting the urgent need for enhanced workplace protections, regular breast cancer screening programs for exposed workers, substitution of safer alternatives where possible, and recognition of breast cancer as an occupational disease for workers with documented exposure to these carcinogens.
2019
Int Arch Occup Environ Health
A systematic review and meta-analysis of 30 studies (with meta-analyses conducted on 13 studies) examined the association between occupational ethylene oxide (EO) exposure and risk of lympho-hematopoietic cancers (LHC) and breast cancer. The overall pooled meta-relative risk was 1.48 (95% CI: 1.07-2.05) for LHC and 0.97 (95% CI: 0.80-1.18) for breast cancer, with meta-RRs for LHC among EO production workers at 1.46 and sterilization workers at 1.07, neither reaching statistical significance. Notably, a clear temporal trend emerged showing substantially higher LHC risk estimates in earlier studies from the 1980s (meta-RR = 3.87) that progressively declined in more recent decades, with studies from the 2000s and 2010s showing meta-RRs of 1.05 and 1.19 respectively, neither statistically significant. The authors conclude that the most informative and methodologically rigorous epidemiological studies published in recent decades do not support an association between occupational ethylene oxide exposure and increased risk of either lympho-hematopoietic cancers or breast cancer, suggesting that earlier positive findings may have been influenced by methodological limitations, exposure misclassification, or confounding factors that have been better controlled in more recent research.
2018
Environ Res
A systematic review of 158 studies examining environmental chemicals and breast cancer found the strongest evidence for increased risk from exposures during critical developmental periods (in utero, adolescence, pregnancy) to DDT, dioxins, PFOSA, air pollution, and occupational solvents, with risk estimates ranging from 1.4 to 5 times higher. A landmark 50-year study that captured DDT exposure during windows of breast development showed particularly elevated risks, while research on genetic variations found that women with certain DNA repair gene variants had higher breast cancer risk from PAH (polycyclic aromatic hydrocarbon) exposure. However, most studies failed to assess exposure timing during biologically relevant windows of susceptibility, and many current-use chemicals in consumer products remain inadequately studied, with major challenges including reconstructing decades-old exposures and measuring rapidly metabolized chemicals in complex real-world mixtures.
2014
Environ Health Perspect
This review of exposure biomarkers for chemicals potentially linked to breast cancer identified methods for 102 chemicals causing mammary tumors in rodents, finding biomarkers for nearly 75% of them, with human exposure biomarkers existing for 62 chemicals (45 measured in non-occupationally exposed populations) and the CDC tracking 23 of them. Among rodent mammary carcinogens with >50% population detection frequency were PAHs (98%), methyleugenol (98%), PFOA (>50%), chlordane (>50%), acrylamide (>50%), and benzene (>50%), indicating near-universal exposure to multiple mammary carcinogens, with several additional chemicals showing >50% detection of urinary metabolites including ethylene oxide, acrylonitrile, fenvalerate, and vinyl chloride (71-75%). The study found consistent carcinogenicity between humans and rodents for many chemicals, though limited data exists for direct effects in humans, and emphasizes the availability of biomonitoring tools and resources to advance breast cancer prevention efforts. The findings underscore that populations are ubiquitously exposed to multiple known mammary carcinogens simultaneously, highlighting the urgent need for biomonitoring programs to assess mixed exposures and inform prevention strategies targeting modifiable environmental risk factors for breast cancer.