While the history of milk banking is rich and evolving, today’s donor human milk systems are built on a foundation of safety, clinical rigor, and growing scientific understanding. This post walks through the essential elements of how milk banks operate, what ensures the safety of the milk, and how donor milk is used in clinical settings.

Eligibility, Screening, and Medical Clearance

Donor human milk is only as safe as the systems that screen and monitor those who provide it. That’s why eligibility and screening for milk donors is both rigorous and standardized, designed to protect recipients—especially premature or medically fragile infants—without creating unnecessary barriers to donation.

Eligibility begins with the basics: donors must be currently lactating and producing more milk than their own baby needs. Most nonprofit milk banks accept donors up to a year postpartum, though some accept donations from parents in their second year of lactation if milk is intended for full-term infants (HMBANA, 2024). Donors must be in good general health and committed to following safe expression, storage, and transport guidelines.

Screening Process

• A detailed health and lifestyle questionnaire, similar to that used for blood donation, screens for risk factors such as recent travel, infections, or exposure to environmental toxins (Unger et al., 2024).

• Potential donors provide a list of all prescription and over-the-counter medications, herbal supplements, and vitamins. Certain substances—such as antineoplastics, radioactive agents, and some psychiatric medications—exclude donation due to potential risks to infants. Others, like limited use of certain SSRIs or thyroid medications, may be reviewed on a case-by-case basis (Peila et al., 2017; Quitadamo et al., 2021).

• Donors must be non-smokers, abstain from recreational drug use, and limit alcohol intake. HMBANA guidelines exclude any milk expressed within 12 hours of alcohol consumption (HMBANA, 2024).

• Importantly, all approved donors must obtain written medical clearance from both their own healthcare provider and their infant’s provider, confirming that donation is safe and that the infant is growing well and receiving adequate milk.

After these steps, potential donors undergo blood testing for infectious diseases, including HIV-1 and HIV-2, human T-cell lymphotropic virus (HTLV) types I and II, hepatitis B and C, and syphilis. The bloodwork must be completed at a certified lab and is reviewed by medical staff at the milk bank before approval (Unger et al., 2024).

Throughout the donation period, ongoing eligibility is monitored. Donors are required to notify the bank of any changes in health status, medication use, or lifestyle that could impact milk safety. Regular communication with donor coordinators helps maintain a high level of vigilance.

These practices are grounded in ethical milk banking principles: donors are never paid, which helps preserve altruistic intent and reduces the risk of unsafe donation due to financial pressure. Instead, they are supported through education, access to lactation support if needed, and sometimes small tokens of appreciation such as thank-you notes or certificates.

Collection, Storage, and Transportation Protocols

Once donors are approved, they are carefully trained in safe milk expression, storage, and handling procedures. This ensures that milk collected at home maintains its nutritional and immunological quality—and that it remains microbiologically safe for medically vulnerable recipients.

Collection

While milk may be expressed using either hand expression or a breast pump, donors are instructed to:

• Wash hands thoroughly before each expression session.

• Use clean, sterilized containers—typically sterile, single-use plastic bottles or glass jars with secure lids.

• Label containers immediately with the date and time of expression.

• Store milk promptly in a freezer set to –18°C (0°F) or colder, ideally within 24 hours if previously refrigerated (Unger et al., 2024; HMBANA, 2024).

Many milk banks provide sterile containers and storage bags, and offer guidance on pump cleaning and handling of milk. Some banks discourage the use of certain plastic bags or containers that may leach chemicals or degrade during freezing (Moro et al., 2020).

Donors are also instructed to monitor for signs of contamination, such as unusual odors, discoloration, or milk that appears curdled—although these may not always indicate a safety issue, they warrant discussion with the milk bank.

Transportation

Transportation of donor milk is a critical part of maintaining safety and quality. Frozen milk must remain frozen until it reaches the milk bank:

• Local donors may deliver milk in person, often using coolers with ice packs or dry ice.

• Remote donors typically ship milk via overnight courier in insulated containers packed with dry ice. Banks provide detailed instructions to ensure milk remains frozen throughout transit (Unger et al., 2024; HMBANA, 2024).

Upon receipt, milk is logged into the bank’s tracking system using unique barcodes or ID numbers, ensuring full traceability from donor to recipient. Each container is visually inspected, labeled, and placed in quarantine freezers until processing. Milk that arrives thawed, improperly labeled, or from donors with expired eligibility is discarded.

Milk banks maintain strict cold chain management. Freezers are monitored continuously, and alarm systems are in place to detect temperature excursions. Chain-of-custody documentation ensures that every ounce of milk can be tracked at each stage of handling—from the donor’s freezer to the recipient’s bedside (Quitadamo et al., 2021).

These meticulous collection and transportation protocols are designed to preserve the biological integrity of milk while protecting it from contamination. Proper handling not only supports infant safety but also reinforces the trust of families and clinicians in the donor milk system.

Pasteurization and Batch Testing

Once donor milk is collected and stored, the next critical step in ensuring its safety is pasteurization. Human milk banks accredited by HMBANA and other international organizations use the Holder pasteurization method, a scientifically validated process that carefully balances microbial safety with preservation of milk’s bioactive properties.

The Holder Method: Safety Through Heat

The Holder method involves heating pooled donor milk to 62.5°C (144.5°F) for 30 minutes, followed by rapid cooling to 4°C (39.2°F) or below. This temperature-time combination is well established to inactivate a wide range of pathogens—including:

• Viruses such as HIV, CMV, HTLV, and hepatitis B and C

• Bacterial pathogens including E. coli, Staphylococcus aureus, and Listeria monocytogenes (Peila et al., 2017; Quitadamo et al., 2021)

While flash-heat or ultraviolet pasteurization methods are being explored in research settings, the Holder method remains the gold standard in nonprofit milk banking due to its consistency, proven efficacy, and regulatory acceptance (Unger et al., 2024).

Pooling and Batch Processing

Before pasteurization, milk from one donor or multiple donors may be pooled together in sterile conditions to create standardized batches. Pooling helps ensure consistency in nutrient composition and volume availability. However, pooling is only done when:

• All milk is from approved donors with current serologic testing

• All milk has been properly stored, labeled, and logged

• The batch size complies with the milk bank’s protocols for donor tracking and quality control (HMBANA, 2024)

The pooling process is conducted in sterile environments, using equipment and containers that are cleaned and sanitized to food-grade or medical-grade standards.

Microbial Testing: Before and After

Microbiological testing is conducted at two key points:

Pre-pasteurization testing: A small sample of the pooled milk is cultured to check for bacterial contamination before pasteurization. If the bacterial load exceeds acceptable levels, the milk is discarded before processing.

Post-pasteurization testing: After pasteurization, another sample is cultured. The goal is zero bacterial growth. Any batch that tests positive for contamination—no matter how minor—is immediately discarded (Unger et al., 2024; HMBANA, 2024).

This double-testing model is essential to ensuring high levels of microbiological safety, especially for immunocompromised infants in NICUs.

Storage After Pasteurization

Approved, pasteurized donor milk is stored in deep freezers at –20°C or colder, often in secure, monitored medical freezers with alarm systems and backup power. Milk is labeled with barcodes that track:

• Donor identity

• Pooling batch

• Pasteurization date

• Expiration date

• Final microbial testing results

Typically, pasteurized donor milk is considered safe for use up to 3–12 months, depending on storage conditions and protocols (Unger et al., 2024).

Pasteurization and batch testing are the critical control points that turn raw human milk into a reliable, regulated clinical product. These processes are not just about temperature—they reflect decades of research, safety innovation, and commitment to the infants who need this life-saving resource most.

Nutritional and Immunological Value of PDHM

While donor milk undergoes pasteurization to ensure safety, it still retains many of the key nutritional and bioactive components that make human milk the optimal food for infants. For medically fragile babies—particularly those born preterm—this can be a critical lifeline.

Retained Bioactive Components

Despite the heating process involved in Holder pasteurization, PDHM still contains numerous beneficial components:

• Human milk oligosaccharides (HMOs) remain largely intact and continue to function as prebiotics that shape the infant’s gut microbiome and prevent pathogen adhesion

• Lactoferrin, though reduced, maintains some antimicrobial activity and supports iron absorption

• Secretory IgA levels drop significantly, but traces remain and may still offer mucosal protection

• Cytokines, growth factors, and hormones such as epidermal growth factor (EGF) and insulin-like growth factors can survive pasteurization to varying degrees (Peila et al., 2017; Quitadamo et al., 2021)

Thus, while pasteurized donor milk is not identical to raw mother’s milk, it far surpasses infant formula in terms of immunological and developmental support, especially for fragile newborns.

Donor milk may also help support the infant’s developing gut microbiome—particularly when used in conjunction with maternal milk or probiotics. While pasteurization eliminates live microbes, the preserved HMOs and antimicrobial peptides can influence microbial colonization in beneficial ways (Unger et al., 2024).

In sum, PDHM preserves many of the most vital components of human milk. Though not a perfect replacement for mother’s own milk, it provides the next best option, especially when fortified appropriately. In both short- and long-term outcomes, PDHM offers advantages over formula—nutritionally, immunologically, and developmentally.

Clinical Use in NICUs and Beyond

The use of pasteurized donor human milk (PDHM) has become a cornerstone of neonatal nutrition, particularly in neonatal intensive care units (NICUs) caring for vulnerable infants. While mother’s own milk remains the gold standard, PDHM provides a life-saving alternative when maternal milk is unavailable, insufficient, or contraindicated.

In the NICU: Life-Saving Nutrition for the Smallest Patients

The most common and evidence-supported use of donor milk is for very low birth weight (VLBW) infants, defined as those weighing less than 1500 grams at birth. These infants face serious health risks, including:

• Necrotizing enterocolitis (NEC), a devastating gastrointestinal disease with high morbidity and mortality

• Sepsis and other infections due to immature immune systems

• Feeding intolerance, which can delay growth and increase dependence on parenteral nutrition

Multiple randomized controlled trials and meta-analyses have shown that VLBW infants fed human milk—either maternal or donor—have significantly lower rates of NEC and other complications compared to those fed formula (AAP, 2017; Peila et al., 2017). The protective effects are so profound that the American Academy of Pediatrics recommends donor milk as the preferred alternative to maternal milk for preterm infants in the hospital setting (AAP, 2017).

Most NICUs using PDHM implement a tiered feeding protocol:

1. Mother’s own milk is always prioritized.
2. PDHM is used as a bridge or supplement when maternal milk is unavailable or delayed.
3. Formula is used when neither maternal nor donor milk is available.

PDHM is often fortified to meet the higher nutritional needs of preterm infants and carefully monitored to ensure adequate growth.

Use Beyond the NICU

Although NICUs remain the primary setting for donor milk use, its application is expanding in outpatient and community settings. These include:

• Post-discharge support for preterm or medically complex infants who continue to need human milk but whose mothers are unable to fully lactate

• Congenital conditions, such as gastrointestinal malformations or cardiac defects, where human milk’s digestibility and immune protection are critical

• Infants with formula intolerance, severe allergies, or metabolic disorders, where donor milk may be better tolerated

• Adopted infants, when adoptive parents wish to provide human milk and lactation induction is not possible or sufficient

• Temporary maternal illness or medication use, where breastfeeding is interrupted but donor milk can fill the gap

While these expanded uses show promise, access outside of the NICU remains uneven. Barriers include cost, limited supply, lack of provider awareness, and insurance reimbursement restrictions. In most U.S. states, Medicaid and private insurance cover PDHM in the NICU but not in outpatient settings, although advocacy efforts continue to change this landscape (Unger et al., 2024).

Equitable Access as a Clinical and Ethical Imperative

Equity is increasingly recognized as an essential consideration in donor milk distribution. Infants born to marginalized populations—such as Black, Indigenous, and Latinx families—are disproportionately born preterm and at higher risk for complications like NEC, yet may have less access to PDHM due to systemic inequities and hospital resource disparities (Unger et al., 2024).

Milk banks and public health advocates are working to address these gaps by:

• Expanding Medicaid coverage for outpatient donor milk

• Creating hospital donation and access programs in underserved communities

• Educating clinicians and families about when and how to access PDHM

The clinical use of PDHM represents both a scientific achievement and a public health responsibility. In NICUs, its benefits are well established. Expanding access beyond the hospital walls—while ensuring ethical, equitable distribution—represents the next frontier in donor milk care.

Looking Ahead

The science and systems behind donor milk banking are a testament to how far we’ve come in protecting infant health. From rigorous donor screening to precise pasteurization and clinical application, every step in the process is built to ensure that human milk remains both safe and life-saving—especially for our most vulnerable infants.

As lactation professionals, understanding the inner workings of milk banking empowers us to advocate more effectively, educate with confidence, and guide families through feeding choices rooted in both compassion and science. Donor milk is not just a substitute—it’s a powerful tool in our clinical toolbox, backed by decades of research and public health commitment.

Coming up in Part 3: We’ll explore the global landscape of human milk banking—highlighting how milk banks operate around the world, the cultural and systemic barriers that affect access, and the ethical considerations shaping donor milk distribution. From international best practices to challenges in equity and sustainability, we’ll examine what it takes to ensure that lifesaving donor milk is available to every infant who needs it.

References

American Academy of Pediatrics. (2017). Donor human milk for the high-risk infant: Preparation, safety, and usage options in the United States. Pediatrics, 139(1), e20163440. https://doi.org/10.1542/peds.2016-3440

Bloom, B. T. (2016). Safety of donor milk: A brief report. Journal of Perinatology, 36(4), 392–393. https://doi.org/10.1038/jp.2015.207

Human Milk Banking Association of North America. (2024). HMBANA standards for donor human milk banking: An overview.

Peila, C., Moro, G. E., Bertino, E., Cavallarin, L., Giribaldi, M., Giuliani, F., Cresi, F., & Coscia, A. (2016). The effect of Holder pasteurization on nutrients and biologically-active components in donor human milk: A review. Journal of Pediatric Gastroenterology and Nutrition, 8(8):477. doi: 10.3390/nu8080477.

Perrin, M. T., Fogleman, A. D., Newburg, D.S., & Allen, J.C. (2016). A longitudinal study of human milk composition in the second year postpartum. Maternal & Child Nutrition, 13(1), e12239. https://doi.org/10.1111/mcn.12239

Quitadamo, P. A., Giuseppina, P., Cianti, L. Lurdo, P. Gentile, M. A., & Villani, A. (2021). The revolution of breast milk: The multiple role of human milk. International Journal of Pediatrics, 2021, 8814552. https://doi: 10.1155/2021/6682516.

Unger, S. & O’Connor, D.  (2024). Review of current best practices for human milk banking. Maternal & Child Nutrition, Suppl 4(Suppl 4):e13657. doi: 10.1111/mcn.13657.