Bottom Line Up Front: Dry ice can rupture your milk storage bags, freeze-burn your supply, trigger expensive hazmat surcharges, and even get your package refused at the drop-off counter. There are safer, simpler, and often cheaper alternatives available to pumping moms today.

You’ve spent weeks — maybe months — building up your freezer stash. Now you nee to ship it, and the first thing that comes to mind is dry ice. After all, it’s cold, it’s available at most grocery stores, and it sounds like exactly what you need.

But here’s what you don’t know….

What Dry Ice Actually Does Inside a Shipping Box

Dry ice is solid carbon dioxide (CO₂) sitting at –109.3°F  dramatically colder than the standard freezer temperature of 0°F  that breastmilk requires. Rather than melting into liquid, it sublimates: it converts directly into CO₂ gas inside a sealed container.

That process creates two invisible threats to your shipment:

• Extreme cold: Temperatures far below what breastmilk storage bags are rated for. Most standard milk bags become brittle and crack at these temperatures.
• Pressure buildup: CO₂ gas expands inside any sealed container. If it can’t escape, the cooler pops open — or worse, bursts — during transit.

7 Reasons Dry Ice Is Risky for Breastmilk Shipping

1. It Can Rupture Your Milk Storage Bags

Dry ice is so cold that it makes plastic breastmilk storage bags extremely brittle. Direct or near-direct contact will cause them to crack and split during transit — spilling your entire stash inside the box. La Leche League USA explicitly warns that dry ice should never come into direct contact with milk bags for this exact reason. If you have to use it,  separate with newspaper or cardboard — but even then, the extreme cold poses a risk to thin-walled pouches.

2. It’s Classified as a Hazardous Material

Both the U.S. Department of Transportation (DOT) and the International Air Transport Association (IATA) classify dry ice as a dangerous good. That means your package requires special hazmat labeling, shipper certifications, and documentation. If you’re not familiar with these requirements, your package can be refused, delayed, or subject to steep fines!

3. Not All Drop-Off Locations Accept It

Many FedEx and UPS locations will not accept packages containing dry ice. You may need to call ahead to multiple locations to find one that will. This creates logistical chaos on the very day you’re trying to ship.

4. The Weight Limits Are Surprisingly Strict

FedEx limits dry ice to just 2.2 lbs per package for most shipments and requires that packages containing dry ice be picked up — not dropped off — at a shipment center. UPS allows a maximum of 5.5 lbs of dry ice per package for air and ground shipments. These limits are easy to exceed when you’re packing enough to keep milk frozen over a 1–2 day transit window, especially in summer.

5. It Can Cause an Explosion Inside the Cooler

Dry ice sublimates into CO₂ gas continuously. If your cooler lid is sealed airtight, pressure will build until the container pops open or bursts during transit. For this reason, you must never tape the lid of a cooler when using dry ice — but a loose lid also means reduced insulation, creating a catch-22 for maintaining temperature.

6. It’s Dangerous to Handle Without Proper Protection

Prolonged skin contact with dry ice causes injuries similar to burns — called cryogenic burns. You need insulated gloves, protective eyewear, and should never handle it in a small enclosed space, as the sublimating CO₂ can displace oxygen and pose a suffocation risk. For a sleep-deprived, time-strapped pumping mom, this extra safety overhead is a real burden.

7. The USPS Won’t Accept It At All

Which is fine because you shouldn’t be shipping with USPS in the first place! Read our blog on why you shouldn’t ship your breastmilk with USPS.

Safer Alternatives That Save The Milk Uses That Actually Work

1.  We Use Gel Ice Packs

Phase-change gel packs are specifically designed to maintain freezing temperatures for 24–48+ hours. Unlike dry ice, they don’t require hazmat labeling, can be reused, and won’t destroy your milk bags. Use multiple packs and place them on all sides of your milk — top, bottom, and sides.

2. We have Insulated Shippers

2-inch styrofoam shippers, keep contents frozen for up to 48 hours. They’re reusable and available through Save The Milk.

3. Specialized Breastmilk Shipping Services

Services built specifically for pumping moms handle the packaging, labeling, and carrier coordination for you — no hazmat headaches. Save The Milk’s shipping service is designed exactly for this: pre-tested, compliant packaging that protects your supply from door to door, with none of the dry ice drama.

4. Discounted Pre-Made Shipping Labels

One of the biggest hidden costs of DIY breastmilk shipping is the label itself. Buying directly at a FedEx or UPS store means paying full retail rates. Save The Milk’s shipping label service lets you purchase pre-made FedEx and UPS labels at steeply discounted rates — saving you money while ensuring your label meets all the requirements for breastmilk shipments.

5. Our Solutions

Overnight and 2nd-day shipping options combined with gel packs is often the most reliable and cost-effective solution — with zero regulatory complexity.

Common Questions

What happens if my breastmilk partially thaws in transit? If milk is still partially frozen with visible ice crystals, it’s safe refreese. Once breastmilk has fully thawed, it should never be refrozen. If milk has thawed but still very cold, use it within 24 hours.

Do I need to label a breastmilk shipment as a biohazard? No. Breastmilk does not require biohazard labeling. If you order a shipping kit through Save The Milk, we include Perishable Stickers so you’re all set. 

Ready to ship without the stress? Save The Milk’s breast milk shipping service handles the hard part so you can focus on what matters.