Breast milk from mothers around the world contains a wide range of endocrine disrupting chemicals (EDCs) – such as bisphenols, perfluorinated chemicals, pesticides, flame retardants, and plasticizers – that can disrupt hormones and potentially harm development, a new study finds. 

The researchers note that human milk is still the best recommended nutrition for infants. The World Health Organization advises exclusive breastfeeding for the first six months of life because human milk protects infants from infections and bestows lifelong benefits, including lower risks of learning disabilities, diabetes, obesity, and hypertension.

“Nursing infants can be exposed to mixtures of EDCs via breast milk, which may carry risks for early-life development, particularly for neurodevelopment and thyroid function,” said principal investigator Dr. Katherine E. Manz, an assistant professor in the Department of Environmental Health Sciences at the University of Michigan’s School of Public Health. 

“However, the overall health benefits of breastfeeding are still clear and substantial. It’s important not to discourage breastfeeding, but rather to focus on creating environments that limit maternal exposure to these chemicals whenever possible.”

The findings point to the need for better understanding and regulation of chemical exposures that accumulate in women’s bodies and may be passed on to children through breastfeeding—a route the authors say has been long overlooked.  

The global review of 71 English language studies, recently published [November 25] in Current Environmental Health Reports, documented measurable levels of chemicals produced by industry known to influence hormones involved in growth, brain development, metabolism, and immune function. 

The most common health problems linked to early exposure to endocrine disruptors in breast milk were effects on brain development and changes in normal thyroid hormone levels, the review shows. The strongest negative impacts on brain development were tied to higher levels of flame retardants and pesticides.

For instance:

• Higher exposure to polybrominated flame retardants (PBDEs) was linked to lower scores on the Bayley developmental tests, which measure thinking, movement, and social-emotional development in infants and toddlers. 
• Numerous organochlorine pesticides (OCPs) in breast milk were linked to poorer cognitive and language outcomes later in childhood, with some associated with a greater risk of ADHD.
• Children whose mothers had higher levels of a flame retardant in breast milk were 3.3 times more likely to have increased outward-directed (externalizing) behaviors, such as impulsivity, according to the Infant-Toddler Social and Emotional Assessment (ITSEA). 

In addition to neurodevelopmental toxicity, numerous studies found associations between the amount of chemicals in breast milk and altered thyroid hormone levels, the authors wrote.

For instance, one study noted an association between thyroid hormone imbalance in mothers and PBDE accumulation, specifically in human milk shortly following delivery. Another found that certain pesticides in breast milk were associated in babies’ cord blood at birth with lower levels of thyroid-stimulating hormone (TSH) and the hormone IGF-1, which plays an important role in childhood growth.

Endocrine disruptors enter the body through inhalation, ingestion, or skin contact and have previously been detected in umbilical cord blood and the placenta. Because many EDCs build up in the body over time, they may move into breast milk during lactation, the study suggests.  

Although concentrations of the chemicals varied widely by region and chemical type, the scientists say 13 of the studies reported that infants were ingesting higher exposure levels of endocrine-disrupting chemicals than recommended in human milk. 

However, the studies did not assess daily intake in a consistent way, the reviewers say. Only two applied the safety criteria recommended for infants. The others estimated exposure in newborns using the same safety limits as for adults, adjusting only for the baby’s body weight.

Studies showed the presence of:  

• Bisphenols (such as BPA)—used in food can linings, plastic containers, and thermal receipts—were detected worldwide. These chemicals can mimic hormones, and early-life BPA exposure has been linked in other studies to increased risks of heart disease, stroke, type 2 diabetes, and obesity later in life.
• Organochlorine pesticides (OCPs)—many of which were used in agriculture and pest control and persist in soil and food—were detected frequently, including 36 different chemicals across 11 studies. Past research has linked exposures to childhood cancers, neurological disorders, infertility, premature birth, and metabolic and reproductive problems.
• Polybrominated flame retardants (PBDEs)—used in furniture foam, electronics, and textiles—and polychlorinated biphenyls (PCBs), which were once used in electrical equipment and industrial materials and still linger in soil, water, and food, were detected in all 10 studies that assessed them. Exposure has been associated with lower infant developmental scores, greater risk of behavioral problems, and thyroid hormone disruption.
• Per- and polyfluoroalkyl substances (PFAS, or “forever chemicals”)—used in nonstick cookware, stain-resistant fabrics, food packaging, and industrial processes—were commonly detected, including PFOA and PFOS. These chemicals may be more concentrated in early milk, the study suggests. Exposure has been associated with cancer, thyroid disease, liver damage, weakened immunity, and developmental problems.
• Phthalates—commonly found in plastics, personal-care products, and food packaging—were commonly detected, with metabolites such as MEHP, MiBP, and MnBP appearing across studies. Although phthalates leave the body quickly, they are widespread in consumer goods. Early-life exposures have been linked to reproductive issues, metabolic disease, and neurodevelopmental problems.
• Parabens—common preservatives used in lotions, cosmetics, shampoos, and some packaged foods—were identified across 10 studies, with methylparaben appearing in all of them. As endocrine disruptors, parabens may be linked to reproductive problems, breast cancer, obesity, and thyroid disorders.
• Polycyclic aromatic hydrocarbons (PAHs)—a type of air pollutant produced by fossil-fuel combustion, traffic exhaust, tobacco smoke, and industrial emissions—were frequently detected. Exposure to PAHs has been associated with metabolic, respiratory, reproductive, and developmental problems.

Even with these associations, the researchers say that the concentration of chemicals found in studies at a given moment do not determine risk alone. Many accumulate in the body over time. In addition, safety thresholds vary internationally and often are not designed specifically for infants, the researchers note. Some studies estimated infant exposure above recommended limits, while others found levels below them. 

The differences from region to region may be due changing regulations, differences in industrial activity, environmental contamination, occupation, and natural shifts in milk composition across lactation, the authors note. Few studies track infants over time, and collection methods lack consistency, complicating comparisons.

Standardized sampling and more data from diverse populations could help scientists better understand how chemical exposures during infancy may shape long-term health, the authors say. To truly understand the risks posed to breastfeeding infants, they say it’s essential to know how chemicals move into human milk and how a mother’s level of exposure affects the amount of endocrine-disrupting chemicals in her milk.

“In future studies, there should be a focus on improving detection techniques, incorporating quality control measures, and assessing EDC exposure across multiple biological matrices over time to obtain more precise exposure estimates in nursing infants,” they said. 

“Further, more robust data is needed to characterize EDC levels by both population and region and to clarify their associations with adverse health outcomes to inform more comprehensive lactation recommendations.”

To reduce exposure to endocrine-disrupting chemicals, choose fresh foods over packaged ones. Select personal care products that are labeled “phthalate” free. Also filter drinking water, regularly clean with a HEPA-filter vacuum or use an air purifier, and avoid unnecessary pesticides around the home.   

Reference

Dunn F, Sullivan H, Romano M, Chambers CD, Braun JM, Manz KE. Endocrine disrupting chemicals in human milk: A systematic review of concentrations and potential health implications. Current Environmental Health Reports. 2025;12(1). doi:10.1007/s40572-025-00515-5