Exposure via breast milk refers to the transfer of substances—from medications and environmental chemicals to infectious agents—from a breastfeeding mother to her infant through breast milk. Understanding how to balance the many benefits of breastfeeding with potential risks from these exposures is essential for protecting infant health while supporting maternal well-being.

Understanding How Substances Reach Breast Milk

When a breastfeeding mother is exposed to certain substances, whether through the environment, her workplace, medications she takes, or infections she may have, there is often concern about whether these can pass to her baby through breast milk. The reality is that nearly any substance present in a mother’s bloodstream has the potential to enter breast milk to some degree. This happens because breast milk is produced from nutrients and other components circulating in the mother’s blood, and substances can move from the blood into the milk through a process called diffusion, which is the natural movement of molecules from areas of higher concentration to areas of lower concentration.^[1][7]

The amount of any substance that actually reaches the infant depends on several interconnected factors. First, the concentration of the substance in the mother’s blood plays a major role—the higher the level in her system, the more likely it is to appear in her milk. Second, the chemical properties of the substance matter greatly. For example, substances that dissolve easily in fat tend to concentrate more in breast milk because milk contains significant amounts of fat. Substances that bind strongly to proteins in the blood are less likely to transfer into milk because they remain attached to those proteins rather than moving freely. Third, the volume of milk the baby consumes affects total exposure—a newborn drinking large amounts of milk several times a day will receive more of any substance present than an older infant who breastfeeds only once or twice daily.^[7][10]

The infant’s own characteristics also influence how exposure affects them. A premature baby or a newborn has an immature liver and kidneys, meaning their body cannot process and eliminate substances as efficiently as an older, healthier baby. The same amount of a substance that might be harmless to a six-month-old could potentially cause problems in a two-week-old. Additionally, during the first few days after birth, when a mother produces small amounts of thick, nutrient-rich colostrum rather than mature milk, the baby consumes less volume, which naturally limits exposure even though substances may transfer more easily during this early period.^[7][10]

Weighing Benefits Against Potential Risks

Despite concerns about exposure to various substances through breast milk, health authorities worldwide consistently emphasize that for the vast majority of situations, the benefits of breastfeeding far outweigh potential risks. Breast milk provides complete nutrition tailored specifically to human infants, supports the development of their immune system, protects against numerous infections and chronic diseases, and promotes optimal brain development. These protective effects are so significant that even when mothers have been exposed to certain environmental chemicals or need to take medications, breastfeeding usually remains the safest and healthiest option for feeding the baby.^[1][3]

The protective properties of breast milk actually help defend infants against some of the very exposures that cause concern. Breast milk contains antioxidants—substances that protect cells from damage—as well as immune factors that can reduce the harmful effects of environmental toxins the baby might encounter. Importantly, many environmental pollutants cause greater harm to a developing baby during pregnancy, when they cross the placenta, than they do through breastfeeding after birth. Once a baby is born, continuing to breastfeed provides the best protection for normal growth and development, even helping to limit damage that may have occurred from exposures before birth.^[15]

Decisions about whether to continue breastfeeding when exposure concerns arise should balance the known or estimated risk to the infant against the well-documented benefits of breastfeeding. In most cases, the protective, nutritional, and emotional advantages of breastfeeding are needed most during times when a mother or baby faces health challenges. Fear and uncertainty often lead healthcare providers to recommend against breastfeeding unnecessarily, which then deprives the infant of crucial benefits exactly when they matter most.^[3][9]

Managing Medication Use During Breastfeeding

Most medications are safe to use while breastfeeding, and mothers rarely need to stop nursing because of medication requirements. Almost any medicine taken by mouth enters breast milk to some extent, but the amount is typically very small—often too small to pose risks to the baby. However, there are exceptions where certain medications can reach higher levels in milk or have effects that make them concerning for nursing infants. This is why it is essential for mothers to discuss every medication and supplement they use with their healthcare provider.^[5][10]

When healthcare providers prescribe medications for breastfeeding mothers, they should select those with the lowest risk profile for infants. Safer medications typically have certain characteristics: they bind strongly to proteins in the blood so less gets into milk, they don’t dissolve easily in fat, they have a short half-life (meaning they leave the mother’s system quickly), and they aren’t well absorbed when taken by mouth (so even if the baby gets some in the milk, little enters the baby’s bloodstream). Providers can also recommend timing doses strategically—for example, taking a once-daily medication right before the infant’s longest sleep period minimizes the baby’s exposure.^[10]

For mothers with mental health conditions requiring treatment during breastfeeding, the priority should be effectively treating the mother, often with medications that worked well during pregnancy if the mother was pregnant recently. Most antidepressants—medications used to treat depression and anxiety—are compatible with breastfeeding. However, specific choices matter: certain selective serotonin reuptake inhibitors (a type of antidepressant) are generally safe, though one called fluoxetine should be avoided if possible. Some medications, such as those containing stimulants, might decrease milk supply, which is an important consideration.^[10]

For mothers with diabetes who are breastfeeding, insulin, metformin, and second-generation sulfonylureas are generally the preferred treatments because they have been studied and found to be safe. Newer diabetes medications require more caution because they have not been as thoroughly studied during lactation. For asthma and allergies, inhaled medications for asthma and nasal sprays for allergic rhinitis are unlikely to affect breastfed infants because very little of the medication enters the mother’s bloodstream when used this way. When pain relief is needed, acetaminophen and ibuprofen are the preferred choices during breastfeeding.^[10]

Certain medications are known to be problematic during breastfeeding and should be avoided or used only with extreme caution and close monitoring. These include anticancer drugs (which can cause serious blood and bone marrow problems), lithium (used for certain mental health conditions), oral retinoids (used for severe skin conditions), high doses of iodine, amiodarone (a heart medication containing iodine), and gold salts (used for some rheumatic conditions). Radiopharmaceuticals—radioactive substances used for certain medical imaging tests or treatments—can accumulate in breast tissue and increase risk to the infant, so their use requires specific guidance about temporarily stopping breastfeeding.^[11][12]

One important challenge mothers face is that medication package inserts often include warnings about breastfeeding even when the medication is actually safe to use. This happens because drug manufacturers are not required to conduct studies on medication safety during breastfeeding when seeking approval for new drugs—it would be unethical to deliberately expose infants to potential harm in research studies. As a result, package information may say “do not take if breastfeeding” or “consult your doctor” simply because the manufacturer lacks data, not because there is evidence of harm. Mothers should not rely solely on package inserts but should discuss medication safety with knowledgeable healthcare providers who can access current, authoritative resources on drug safety in lactation.^[7]

Environmental and Occupational Chemical Exposures

Breastfeeding mothers may be exposed to various chemicals in their surroundings, whether at home, in their communities, or through their work. While these exposures can be concerning, mothers should try to reduce or eliminate contact with environmental chemicals as much as possible while continuing to breastfeed, since the benefits of breastfeeding still outweigh potential risks from most common environmental exposures.^[1][2]

Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals used in products such as non-stick cookware, water-repellent clothing, stain-resistant fabrics, some cosmetics, and items that resist grease, water, and oil. Babies can be exposed to PFAS while breastfeeding because these chemicals can accumulate in a mother’s body and transfer into milk. However, given current scientific understanding, the benefits of breastfeeding outweigh any potential risks of PFAS exposure through breast milk. Mothers with concerns should discuss them with their healthcare provider rather than stopping breastfeeding.^[1]

Pesticides are chemicals used to control unwanted vegetation, insects, rodents, or fungi, and they are used in many workplaces and homes. Exposure can occur by breathing them in, eating foods sprayed with pesticides, or absorbing them through the skin. Some pesticides may pass into breast milk, but studies on the effects of this exposure are limited, so the safe level of exposure for breastfeeding is not clearly known. Mothers should reduce their exposure by washing or peeling fruits and vegetables, avoiding unnecessary use of pesticides in and around the home, and following safety recommendations if they work with these chemicals.^[1]

When used according to directions, EPA-registered insect repellents are safe and effective for breastfeeding women. However, mothers should keep repellent away from the nipple area so their baby does not get any in his or her mouth while feeding. Repellents should be used only when needed, applied according to label directions, and washed off when the person is no longer exposed to insects.^[1]

Lead exposure is particularly concerning because no safe blood lead level has been identified, and even low levels can harm a child’s intelligence, attention, and academic achievement. Women can expose their babies to lead during breastfeeding if they have lead in their blood from current exposure or from lead stored in their bones being released during lactation. For mothers with blood lead levels between 5 and 39 micrograms per deciliter, breastfeeding can continue, but the infant’s blood lead levels should be monitored. If maternal levels reach 40 micrograms per deciliter or higher, mothers are encouraged to pump and discard their milk until levels drop below that threshold.^[13]

Occupational Exposures and Workplace Safety

Some breastfeeding mothers encounter chemicals through their work, but most mothers who work around chemicals can safely breastfeed their babies. The benefits of breastfeeding outweigh the potential risk of exposure to common workplace toxicants for most infants. However, both mothers and employers have responsibilities to minimize exposure.^[2]

Employers should provide all workers, including breastfeeding mothers, with complete information about the chemicals they use and train employees about safe work practices. This is required under workplace safety regulations. Employers should work with breastfeeding mothers to reduce their exposure to occupational toxicants as much as possible through measures such as improved ventilation, protective equipment, modified duties, or other accommodations.^[2][11]

Healthcare workers who handle chemotherapy drugs face special concerns because many of these medications are cytotoxic, meaning they damage or kill cells at very low doses, and some are carcinogens, meaning they can cause cancer with no known safe level of exposure. It is best to reduce or eliminate exposure as much as possible. For breastfeeding mothers exposed to chemotherapy drugs at work, following strict safety protocols and discussing exposure reduction with employers and occupational medicine specialists is essential.^[2][11]

Workers in dry cleaning facilities are exposed to perchloroethylene (PCE), also known as PERC, the most commonly used dry cleaning solvent. Studies show that PCE can enter breast milk if a mother is exposed, with greater amounts found in the milk of women exposed to higher levels over longer periods. Few studies have examined effects on nursing infants specifically, though there are reports of neurological responses in children exposed to PERC. Mothers working in dry cleaning facilities should follow workplace safety measures to reduce exposure.^[2][11]

Laboratory workers in clinical or research settings can potentially be exposed to a wide range of chemicals and agents, including solvents, formaldehyde, and infectious agents. Some chemicals used in laboratories can enter breast milk. Breastfeeding mothers who work with chemicals should talk to their healthcare provider and employer about reducing exposure as much as possible, follow recommended best practices when handling materials, and ensure they use appropriate biological and chemical safety equipment correctly.^[2][11]

Working near diagnostic x-ray sources or receiving an x-ray does not affect breast milk and poses no concerns for breastfeeding. However, workers who handle radioactive materials, such as radioisotopes in healthcare and laboratory settings or radioactive waste, must take precautions to reduce exposure. These workers should speak with their workplace radiation safety officer or their state’s department of radiation protection if they have concerns about breastfeeding.^[2][11]

Infectious Disease Transmission Through Breast Milk

A substantial body of evidence demonstrates both the protective effects of breastfeeding against infections and documents that certain specific infections can be transmitted to infants through breast milk. The fear and anxiety that arise when a breastfeeding mother has an infectious illness are understandable, but uncertainty and lack of knowledge sometimes lead to unnecessarily stopping breastfeeding, which deprives the infant of protective, nutritional, and emotional benefits exactly when they are most needed.^[3][9]

Confirming that an infection was truly transmitted through breastfeeding requires careful investigation. The infectious agent must be demonstrated in the breast milk, a clinically significant infection must develop in an infant through a plausible process, and other possible routes of transmission must be ruled out—including exposure through air, direct contact, or transmission before or during birth. Infectious organisms can reach breast milk either by being secreted into the fluid or cellular components of milk or by contaminating the milk during or after expression.^[3][9]

Very few illnesses are actually transmitted via breast milk. The unique properties of breast milk help protect infants from colds and other typical childhood viruses rather than spreading them. Most infections a mother might have do not require stopping breastfeeding. However, there are specific situations where breastfeeding is contraindicated (should not be done) or where temporary cessation is advisable based on recommendations from professional organizations concerned with maternal and infant care.^[6][8]

In the United States, mothers living with HIV are generally advised not to breastfeed because HIV can be transmitted through breast milk. However, the context matters: routine prenatal care includes HIV testing, most women with HIV are identified before or during their hospital stay for childbirth, and most have been on antiretroviral therapy (ART), which are medications that suppress the virus. For mothers on effective ART with a sustained undetectable viral load (meaning the virus cannot be detected in blood tests), the risk of transmission through breastfeeding is less than one percent. Additionally, most women with detectable viral loads in the United States do not breastfeed. These factors mean that the already low risk of HIV transmission through a single accidental exposure to another mother’s milk is extremely small.^[8]

It is very unlikely that a child would be at risk for hepatitis B or hepatitis C by receiving another mother’s breast milk. Neither virus can spread from woman to child through breastfeeding or close contact unless there is exposure to blood. Furthermore, most U.S. infants receive hepatitis B vaccination starting shortly after birth, which provides protection. There is no vaccine for hepatitis C, but there is no evidence that breastfeeding spreads this virus either.^[8]

Medical Imaging and Diagnostic Procedures

When breastfeeding mothers require medical testing, concerns sometimes arise about whether the test will affect breast milk or the baby. For most common diagnostic imaging procedures, there is no reason to interrupt breastfeeding. Regular x-rays, including chest x-rays and other diagnostic x-rays, do not affect breast milk because the radiation used in these tests passes through the body and does not remain afterward. Similarly, contrast materials (special dyes) used for computed tomography (CT) scans or magnetic resonance imaging (MRI) are not concerning during breastfeeding—although many medications do pass into breast milk, the tiny amounts of contrast material that enter milk are not harmful to infants.^[8][10]

However, certain nuclear medicine tests that use radiopharmaceuticals require special consideration. These are radioactive substances given to patients for certain types of medical imaging or treatment. Unlike x-rays, these radioactive materials can concentrate in breast tissue and be secreted into milk, potentially exposing the infant to radiation. The specific radiopharmaceutical used, the dose given, and how long it remains in the body determine how breastfeeding should be managed. For some tests, breastfeeding can resume after a waiting period; for others, such as when radioactive iodine 131 is used for certain thyroid conditions, breastfeeding must be stopped completely. Mothers facing these tests should discuss the specific situation with their healthcare team and can pump and discard milk during any required waiting period to maintain their milk supply.^[10][12]

When Breast Milk Mix-Ups Occur

Despite significant efforts to prevent such events in childcare settings and healthcare facilities, expressed breast milk from one mother is occasionally given to another mother’s baby by accident. When this happens, both families need to be notified, but it’s important to understand that the risk of transmitting an infectious disease through a single breast milk mix-up is very small. The unique properties of breast milk actually help protect infants rather than harm them in most situations.^[8]

When a mix-up occurs, specific steps should be taken. The mother whose milk was given to another child should be asked about when the milk was expressed, how it was handled, her medication use, recent infectious disease history, and whether she had cracked or bleeding nipples during milk expression. The family whose child received another mother’s milk should be informed of the event, told that the transmission risk is small, given whatever information is available about the milk, and encouraged to notify their child’s physician. Any decisions about medical management or testing of the infant should be made by the physician and family working together based on the specific situation.^[8]

Reducing Exposure While Supporting Breastfeeding

There are practical steps breastfeeding mothers can take to reduce exposure of themselves and their babies to potentially harmful substances while continuing to provide the benefits of breastfeeding. These steps focus on minimizing contact with environmental chemicals, making safer choices when possible, and maintaining overall health.^[15][16]

Mothers can eat a healthy diet rich in whole grains, fruits, and vegetables while reducing intake of animal fats, where some environmental pollutants tend to concentrate. Washing or peeling fruits and vegetables removes pesticide residues. Staying well-hydrated by drinking plenty of water supports overall health during breastfeeding. Taking a daily multivitamin or continuing a prenatal vitamin helps ensure breast milk contains all needed nutrients. Ensuring adequate intake of omega-3 fatty acids, particularly DHA, supports the baby’s brain development—this can come from foods like fish low in mercury or from supplements.^[16]

Avoiding or minimizing exposure to harmful substances is crucial. Mothers should not smoke cigarettes, use recreational drugs, or drink alcohol while breastfeeding. They should limit contact with common chemicals such as solvents found in paints, non-water-based glues, furniture strippers, dry-cleaned clothes, nail polish, and gasoline fumes. Avoiding breathing smoke and fumes from fires and handling ash carefully protects against toxic exposure. In workplaces with chemical exposures, following safety protocols strictly and discussing accommodation options with employers helps reduce risk.^[15]

If a mother believes she has been exposed to something harmful at work or elsewhere, she should remove and carefully wash her clothes and shoes to avoid bringing toxic chemicals into her home. For mothers with specific exposure concerns, discussing them with a healthcare provider can help determine whether any special precautions are needed or whether breastfeeding can safely continue as usual.^[2][15]

Most common approaches to managing exposure concerns

• Medication safety assessment
  • Selecting medications with favorable properties: high protein binding, low fat solubility, short half-life, and poor oral absorption in infants
  • Timing doses strategically, such as before the infant’s longest sleep period
  • Using topical medications rather than oral when possible
  • Consulting authoritative resources like LactMed for current safety information
  • Continuing medications that effectively treated conditions during pregnancy when appropriate
• Environmental exposure reduction
  • Washing or peeling fruits and vegetables to remove pesticide residues
  • Reducing intake of animal fats where pollutants concentrate
  • Increasing consumption of whole grains, fruits, and vegetables
  • Limiting contact with household chemicals, solvents, and pesticides
  • Using EPA-registered insect repellents according to directions while keeping them away from the nipple area
  • Avoiding smoke, fumes from fires, and handling of ash
• Workplace safety measures
  • Following recommended best practices when handling infectious materials and chemicals
  • Using appropriate biological and chemical safety equipment correctly
  • Working with employers to reduce exposure through improved ventilation, protective equipment, or modified duties
  • Removing and washing work clothes and shoes before entering the home to avoid bringing chemicals inside
  • Consulting workplace radiation safety officers when handling radioactive materials
• Lead exposure management
  • Monitoring maternal and infant blood lead levels when exposure is suspected
  • Continuing breastfeeding when maternal levels are below 40 micrograms per deciliter
  • Temporarily pumping and discarding milk when maternal levels reach or exceed 40 micrograms per deciliter
  • Identifying and eliminating sources of lead exposure in the environment
• Nutritional support
  • Taking a daily multivitamin or continuing prenatal vitamins during breastfeeding
  • Ensuring adequate DHA intake (200-300 milligrams daily) through low-mercury fish or supplements
  • Maintaining good hydration by drinking water throughout the day
  • Limiting caffeine intake to no more than two cups of coffee daily
• Infectious disease precautions
  • Balancing benefits of breastfeeding against known transmission risks for specific infections
  • Following public health guidance for contraindications to breastfeeding in certain situations
  • Understanding that most common illnesses do not require stopping breastfeeding
  • Recognizing that breast milk provides immune protective factors that help defend against infections
• Medical imaging considerations
  • Continuing breastfeeding normally after standard x-rays and diagnostic imaging with contrast materials
  • Following specific waiting periods or stopping breastfeeding when radioactive substances are used for certain nuclear medicine procedures
  • Pumping and discarding milk during required waiting periods to maintain milk supply
  • Discussing timing and safety with healthcare providers before procedures involving radiopharmaceuticals