Exposure via Breast Milk

While breastfeeding provides vital nutrition and protection for babies, certain substances can pass from mother to infant through breast milk. Understanding what can be transmitted and how to minimize risks helps mothers make informed decisions about safely continuing to breastfeed.

Table of contents

• What Is Exposure via Breast Milk
• How Substances Enter Breast Milk
• Environmental Chemical Exposures
• Occupational Exposures
• Medications and Breast Milk
• Infectious Diseases
• Benefits Usually Outweigh Risks
• Minimizing Exposure

What Is Exposure via Breast Milk

Exposure via breast milk refers to the passage of substances from a breastfeeding mother to her infant through the milk she produces. These substances can include environmental chemicals, medications, infectious agents, and other compounds that the mother encounters in her daily life or workplace. The amount and type of exposure varies greatly depending on many factors^[1].

Most substances that a mother is exposed to can potentially reach breast milk to some degree. However, the actual amount that transfers to the infant is typically very small. In general, less than 1% of a drug will pass through breast milk to the baby^[7]. Despite this, understanding these exposures is important because infants are particularly vulnerable, and their developing bodies may respond differently than adults to even small amounts of certain substances.

How Substances Enter Breast Milk

Substances enter breast milk primarily through a process called diffusion, which means they move from the mother’s bloodstream into the milk. The amount that reaches breast milk depends on the concentration in the mother’s blood and the specific properties of the substance^[10].

Several factors determine how much of a substance ends up in breast milk. Medications and chemicals that are highly bound to proteins in the blood tend to stay in the bloodstream and transfer less into milk. Substances that dissolve easily in fat are more likely to enter breast milk because breast milk contains significant amounts of fat. The mother’s body chemistry, the timing of exposure, and how well her body breaks down or eliminates the substance all play important roles^[12].

The infant’s actual exposure depends not only on what’s in the milk but also on how much milk the baby drinks and whether the baby’s digestive system absorbs the substance. A fully breastfed newborn who drinks large amounts of milk may have greater exposure than an older infant who is also eating solid foods and breastfeeds less frequently^[7].

Environmental Chemical Exposures

Breastfeeding mothers may encounter various chemicals in their everyday surroundings. While the benefits of breastfeeding outweigh the potential risk of exposure to chemicals through breast milk for most infants, mothers should try to reduce or eliminate their exposure to environmental chemicals as much as possible^[1].

PFAS (per- and polyfluoroalkyl substances) are man-made chemicals used in non-stick cookware, water-repellent clothing, stain-resistant fabrics, some cosmetics, and products that resist grease, water, and oil. Babies can be exposed to PFAS while breastfeeding. However, given current scientific understanding, the benefits of breastfeeding outweigh any potential risks of PFAS exposure through breast milk^[1].

Pesticides are chemicals used to destroy unwanted vegetation, insect pests, rodents, or fungi. Exposure to pesticides can happen by inhaling them, eating foods that were sprayed with pesticides, or absorbing them through the skin. Some of these chemicals may pass into breast milk, but studies on the effects of this exposure are lacking. Breastfeeding mothers should try to reduce exposure to these chemicals as much as possible by washing or peeling fruits and vegetables and limiting contact with pesticide applications^[1].

Lead is particularly concerning because mothers can expose infants to lead through breast milk, and even low levels of lead in blood have been shown to negatively affect a child’s intelligence, ability to pay attention, and academic achievement. Women who have been exposed to lead can have it in their blood or breast milk either from direct exposure during pregnancy or lactation, or from lead stored in their bones and teeth from prior exposure being released during pregnancy or lactation^[13].

Insect repellents, when used as directed, are safe and effective for breastfeeding women. However, breastfeeding mothers should keep the repellent away from their nipple area so their child does not get any in his or her mouth while feeding^[1].

Occupational Exposures

Some breastfeeding mothers may encounter chemicals through their work. Most mothers who work around chemicals can safely breastfeed their babies. However, mothers should try to reduce or eliminate their exposure to occupational toxicants as much as possible while breastfeeding. Employers should provide mothers with information and training on their potential occupational exposures^[2].

Chemotherapy drugs used to treat cancer are toxic at very low doses. Some are known to cause cancer with no known safe level of exposure. For breastfeeding mothers exposed to chemotherapy drugs at work, it is best to reduce or eliminate exposure as much as possible^[2].

Dry cleaning solvents, particularly perchloroethylene (also known as PCE, PERC, perchlor, or tetrachloroethene), are the most used solvents in dry cleaning facilities. Studies show that PCE can enter breast milk if a mother is exposed. Greater amounts can be found in the breast milk of women exposed to higher amounts of PCE over longer periods^[2].

Laboratory chemicals and agents can potentially expose staff in clinical or research laboratories 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 health care provider and employer about how to reduce exposure as much as possible^[2].

Working near diagnostic x-ray sources does not affect breast milk, and receiving an x-ray also does not affect breast milk. However, workers who handle radioactive materials must take precautions to reduce exposure^[2].

Medications and Breast Milk

Almost any medicine a mother takes by mouth goes into her breast milk. Most of the time this is a tiny amount that is not likely to be a risk to the baby. However, there are exceptions where some medicines can be found in high levels in breast milk^[5].

Most medicines are safe to take while breastfeeding, and most commonly used drugs are relatively safe for breastfed babies. The dose received via milk is generally small and much less than the known safe doses of the same drug given directly to newborns and infants^[12].

The number of adverse reactions to drugs passing through breast milk is small. Warnings about not using a drug in lactation may sometimes be based on just one reported incident. Drug manufacturers are not required to produce clinical data on the safety of the use of a new drug in lactation when applying for a license to market their product, so many drugs are labeled as not recommended during breastfeeding simply because they have not been studied^[7].

Certain drugs are contraindicated during breastfeeding and include anticancer drugs, lithium, oral retinoids, high doses of iodine, amiodarone, and gold salts^[12]. When prescribing medications for a breastfeeding patient, those with the lowest risk to the infant should be selected, and dosing should ideally occur before the infant’s longest sleep interval^[10].

Infectious Diseases

A large body of evidence clearly demonstrates both the protective effects of breastfeeding and documents the transmission of specific infections to infants through breast milk. Documenting transmission of infection from mother to infant by breastfeeding requires not only the exclusion of other possible mechanisms of transmission but also the demonstration of the infectious agent in the breast milk and a subsequent clinically significant infection in an infant^[3].

Few illnesses are actually transmitted via breast milk. Instead, the unique properties of breast milk help protect infants from colds and other typical childhood viruses^[8]. Infectious organisms can reach breast milk either by secretion in the fluid or cellular components of breast milk or by contamination of the milk at the time of or after expression^[3].

In the rare event of a breast milk mix-up where one mother’s milk is accidentally given to another mother’s child, the risk of transmission of infectious diseases is small. The risk of transmission of HIV to an infant who received a single bottle of another mother’s milk is very low. Most US women living with HIV are identified prior to or during their maternity hospital stay and most have been on treatment. Additionally, most women with HIV in the United States do not breastfeed if their viral load is detectable^[8].

It is very unlikely that a child would be at risk for hepatitis B or C by receiving another mother’s breast milk. These viruses cannot be spread from a woman to a child through breastfeeding or close contact unless there is exposure to blood^[8].

Benefits Usually Outweigh Risks

Decisions concerning breastfeeding in a mother with an infectious illness or exposure to chemicals should balance the potential benefits of breastfeeding versus the known or estimated risk for the infant. Uncertainty and lack of knowledge often lead to advising against breastfeeding out of fear, which then deprives the infant of the potential protective, nutritional, and emotional benefits of breastfeeding exactly at the time when they are most needed^[3].

The advantages of breast milk should never be underestimated, nor should the wishes of a mother to continue to breastfeed and the right of the infant to continue to receive it. Taking medication does not usually mean that a mother has to stop breastfeeding temporarily or permanently^[7].

Breast milk provides babies with a defense against environmental toxins. Environmental pollutants have a greater impact on a baby while they are developing inside their mother’s womb during pregnancy, not when being breastfed. After birth, breastfeeding is the best protection that a baby has for normal growth and development. Breast milk contains antioxidants and immune protective factors which can lessen the effects of any environmental toxins a baby is exposed to^[15].

Despite the stark evidence of severe short- and long-term impacts of conflict on women and young children, guidance on breastfeeding safety during chemical and biological threats is often lacking. The abundant guidelines and research available typically focus on the general population rather than providing specific, easy-to-understand information for breastfeeding mothers and infants^[4].

Minimizing Exposure

There are several ways breastfeeding mothers can reduce their exposure and their baby’s exposure to potentially harmful substances. Mothers should avoid smoking cigarettes, using recreational drugs, and drinking alcohol. They can reduce intake of animal fats while increasing intake of grains, fruits, and vegetables. Removing pesticides by washing or peeling fruits and vegetables is helpful^[15].

Breastfeeding mothers 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. They should try to avoid breathing in smoke and fumes and handling ash from fires. Avoiding exposure to toxic chemicals in the workplace is important, and if exposure occurs, removing and carefully washing clothes and shoes helps avoid bringing toxic chemicals into the home^[1].

For mothers concerned about lead exposure, breastfeeding recommendations vary based on the amount of lead in the mother’s blood. Women with blood lead levels between 5 and 39 micrograms per deciliter can breastfeed, though infant blood lead levels should be monitored. Mothers with blood lead levels at or above 40 micrograms per deciliter are encouraged to pump and discard their milk until their levels drop^[13].

Mothers should eat healthy foods and take a multivitamin or prenatal vitamin each day to make sure their breast milk is full of nutrients for their baby. They should drink lots of water to stay hydrated and limit caffeine intake to no more than two cups of coffee per day^[16].

It is important for mothers to discuss any concerns with their health care provider and talk about each medicine and supplement they take. Accurate information from current, reliable resources helps mothers make informed decisions about safely continuing to breastfeed while protecting their babies from unnecessary exposure^[5].