Shipping Breast Milk: Best Practices for Sending Frozen Milk

Shipping breast milk – whether you’re a donor sending milk to a recipient or a parent traveling – requires careful packing to keep the milk frozen and safe. Breast milk is perishable, so the goal is to maintain proper cold temperature during transit. Here are best practices for shipping frozen breast milk:

1. 1Freeze the milk solid and prep it well. Always freeze your milk before shipping. Store it in small, flat quantities (e.g. 3-5 oz per bag) because flatter bags freeze and thaw faster and allow efficient packing. Ensure each storage bag or container is sealed tightly with no air to prevent freezer burn. It’s worth investing in high-quality breast milk storage bags that are less prone to leaks and can be packed tightly (some brands have compact shapes ideal for stacking).
2. 2Use an insulated container. Line a sturdy cardboard box with an insulation layer. The classic approach is a Styrofoam cooler inside a cardboard box. The foam walls should be at least ~1-2 inches thick. Place a large plastic bag or liner inside the cooler to catch any leaks (and to enclose ice packs if they sweat). Note: Styrofoam alone only keeps milk frozen for about a day, so you will need to include cold packs or dry ice (more on that next). There are also advanced insulated shipping kits (like medical-grade coolers with vacuum insulation); these can maintain frozen temps for 2-4 days without ice, but they can be expensive. Many donors simply use a foam cooler and lots of ice packs.
3. 3Add plenty of cold source (dry ice or gel packs). For keeping milk frozen longer than 24 hours, dry ice is highly effective because it’s colder than ice and doesn’t melt into liquid (it sublimates to gas). If you use dry ice, handle it with gloves and follow carrier rules – usually you’re limited to <5 pounds and must label the package “Dry Ice” with the weight. Don’t seal the cooler completely airtight if using dry ice; the CO₂ gas needs to vent, or pressure can build up. Gel ice packs (like reusable freezer packs) are also a good option – they’re food-safe and not as cold as dry ice, but if you use a lot of them, they can keep milk frozen for 1-2 days. Some shippers use a combo: for example, frozen milk sandwiched between frozen gel packs on all sides. Place the milk bags at the bottom of the cooler, then cover with ice packs on top and around, since the top and sides are where warmth can seep in first. Fill any extra air space in the cooler with crumpled paper or more insulation – empty space causes faster warming.
4. 4Ship overnight if possible. The faster the transit, the better. Choose overnight or express shipping so the milk spends minimal time in transit (preferably no more than 24-36 hours). Mark the shipment “Perishable – keep frozen”. You don’t necessarily need to pay for dry ice shipping if you packed with gel packs and it’s overnight, but for longer distances or delays, dry ice provides insurance. Many shipping services allow shipping breast milk, but be aware not all drop-off locations accept packages with dry ice (check with the carrier or pre-ship at a staffed location). FedEx and UPS both have guidelines on shipping perishable items; FedEx even offers a special cold shipping box that keeps 2-8°C for ~48 hours without ice – though that’s fridge temp, not frozen.
5. 5Communication and timing. Ship early in the week (Monday–Wednesday) to avoid weekend delays. Provide the recipient/tracking so someone can immediately transfer the milk to a freezer on arrival. It’s wise to avoid shipments over holidays or bad weather when delays are likely. If you’re the receiver, have space in your freezer ready (or coolers if you plan to keep it on dry ice until use).
6. 6Traveling with milk: If you are transporting milk on a plane or personal travel, frozen milk is allowed through TSA (as a medical/infant feeding item) even when you’re not with your baby. Pack it similarly in a cooler with ice packs. Declare it at security – they may do an extra screening, but breast milk is permitted. For flights, completely frozen bags travel best (solid frozen milk doesn’t count toward liquid limits). Use hotel freezers or dry ice for multi-day trips as needed.

By following these practices – freezing flat, using plenty of insulation and ice, and shipping quickly – many moms successfully ship breast milk across the country with minimal thawing. It’s not uncommon for a well-packed cooler to arrive with milk bags still frozen solid after overnight shipping. If milk does partially thaw in transit but still has ice crystals, it can be safely refrozen upon arrival (fully thawed milk, however, should be used within a day).

In summary, treat breast milk like the precious, perishable cargo it is: keep it cold, keep it fast, and keep it well-packed. This ensures that donated or personal milk reaches its destination intact and safe for baby.