Can You Pass An Infection Through Breast Milk?

Yes, you can pass some infections through breast milk — but far fewer than most people assume. Breast milk itself is not a common route of transmission for most illnesses. The infections that genuinely travel through milk are a short, specific list, and they behave very differently from the ones you catch by coughing or touching a contaminated surface.

The more important point for most parents: in nearly every case where transmission through milk is possible, breastfeeding is still considered beneficial and is usually continued with precautions. Human milk carries antibodies and immune factors tailored to the baby’s environment. The decision about whether to keep nursing during an infection is a clinical one, made with a doctor, not a blanket rule.

Can You Pass An Infection Through Breast Milk?

Only a small number of infections are known to pass to a baby through breast milk. The list is dominated by viruses: HIV, human T-cell lymphotropic virus type 1 (HTLV-1), cytomegalovirus (CMV), and hepatitis B and C under certain conditions. Some bacterial infections can also reach the baby through milk, but this is uncommon and usually tied to mastitis or a skin infection on the breast.

What surprises many people is how short that list is compared with how many infections a parent might have. Colds, flu, strep throat, COVID-19, and most gastrointestinal bugs do not transmit through milk. A sick parent is far more likely to pass those to a baby through breathing, hands, or shared surfaces than through nursing.

The distinction matters. Transmission through milk depends on whether a pathogen can survive in milk, reach the mammary gland, and infect an infant through the digestive tract. Most organisms cannot do all three.

Which Infections Can Actually Be Transmitted Through Breast Milk?

The infections with documented transmission through human milk are well characterized in the medical literature. They fall into viral and bacterial categories, and each has its own pattern.

Viral infections

• HIV. HIV can pass through breast milk. This is well established. The risk is not absolute, and it varies with factors like viral load, duration of breastfeeding, and whether the parent is on effective antiretroviral therapy. In many high-income settings, guidelines advise against breastfeeding when a parent has HIV and safe alternatives exist. In settings where safe formula is not reliably available, guidelines from global health bodies support breastfeeding alongside antiretroviral treatment because the risks of not breastfeeding are substantial. This is a genuinely complex area where the right answer depends on the local context and clinical guidance.
• HTLV-1. This virus, which is uncommon in the US, can be transmitted through breast milk. Guidelines generally advise against breastfeeding for parents who carry HTLV-1 where safe alternatives are available.
• Cytomegalovirus (CMV). CMV can pass through breast milk. For full-term, healthy infants this is generally not a concern. For very premature infants, particularly those born before about 30 weeks, breast milk CMV can occasionally cause symptomatic infection. Some neonatal units freeze or pasteurize milk for this group. This is a decision made by the care team.
• Hepatitis B. Transmission through breast milk is not considered a significant route. The bigger concern with hepatitis B is transmission at birth, which is why infants of parents with hepatitis B receive vaccination and immune globulin shortly after delivery. With that protection in place, breastfeeding is generally supported.
• Hepatitis C. Hepatitis C transmission through breast milk is not well documented and is not considered a major route. Guidance generally supports breastfeeding. One practical caveat: if nipples are cracked or bleeding, some clinicians advise temporarily pumping and discarding milk until the skin heals, because of theoretical blood exposure.

Bacterial infections

Bacterial transmission through milk is uncommon. The scenario clinicians watch for is mastitis — inflammation of the breast tissue, often with infection — where bacteria can be present in milk. Even then, continuing to breastfeed or express milk is typically recommended because emptying the breast helps resolve the inflammation, and the bacteria involved are usually not harmful to a healthy infant’s gut. A skin infection on the breast, such as a staph infection, is a different situation and needs medical evaluation.

What About Colds, Flu, and COVID-19?

These do not pass through breast milk. Respiratory viruses spread through droplets and contact, not through milk. A parent with a cold or flu is contagious to the baby by being close to them, not by nursing them.

Here is the part many parents find counterintuitive: nursing during a respiratory illness is usually protective. When a parent is infected, their body produces antibodies against that specific virus, and those antibodies appear in breast milk. The baby receives them through feeding. This is one of the clearest examples of milk adapting to the environment it is made in.

Practical steps during a respiratory illness are about reducing exposure, not stopping feeds:

• Wash hands before and during feeds.
• Consider wearing a mask while nursing or holding the baby during the most contagious phase.
• Keep surfaces and shared items clean.
• Continue feeding as usual unless a clinician advises otherwise.

COVID-19 follows the same pattern. The virus has not been shown to transmit through breast milk in a way that causes infant infection. Guidance from major health bodies has consistently supported breastfeeding with hygiene precautions when a parent has COVID-19.

What About Infections That Affect the Breast Itself?

When the breast tissue is infected, the situation is different from a systemic illness. The main concern is mastitis, which causes pain, redness, swelling, and often fever and flu-like symptoms.

Current clinical guidance generally supports continuing to breastfeed or express milk during mastitis. The milk is not considered dangerous to a healthy infant, and removing milk helps the breast heal. Some clinicians recommend feeding on the affected side first to encourage drainage. If symptoms are severe, worsening, or accompanied by high fever, medical evaluation is needed — some cases require antibiotics, and a small number progress to an abscess that needs drainage.

One clarification worth knowing: mastitis is not always infectious. It can begin as inflammation from milk stasis — milk not draining well — and only sometimes involves bacteria. That is part of why the approach focuses on drainage and support rather than assuming antibiotics are always needed.

What Should You Do If You Think You Have an Infection?

Talk to your clinician before making any decision about stopping breastfeeding. The right answer depends on which infection you have, your treatment, your baby’s age and health, and what safe feeding alternatives are available to you.

Some general principles hold across most situations:

• Most common infections do not require stopping breastfeeding.
• For infections that can transmit through milk, the decision is individualized and often depends on whether safe alternatives exist.
• If you are on medication, check whether it is compatible with breastfeeding — many are, and some are not.
• Never discard milk or stop feeding based on an internet search alone.

If you have HIV, HTLV-1, or are being treated for a serious infection, this conversation needs to happen with a clinician who knows your full history. The guidance is specific and the stakes are real.

Does Freezing or Heating Milk Kill Infections?

Heat treatment of expressed milk can reduce some pathogens, and Holder pasteurization — a specific controlled heating method used in milk banks — is effective at inactivating many viruses and bacteria. Home freezing is not the same thing. Freezing does not reliably kill HIV, CMV, or most bacteria in milk.

Do not assume that freezing or ordinary warming makes milk safe from a pathogen that can transmit through it. If a clinician has advised against feeding your milk because of an infection, home processing is not a substitute for that guidance.