You’re standing in line. The person in front of you is frantically digging through a designer tote, pulling out a half-used bottle of expensive sunscreen while a TSA agent watches with that specific, tired expression they all seem to share. It's a classic airport scene. Even though we’ve been living with these rules for nearly two decades, the carry on liquid policy remains one of the most consistent points of friction at the airport. It's frustrating. Honestly, it’s mostly because the rules feel a bit arbitrary when you're just trying to get to your gate without losing thirty dollars' worth of face cream.
Let’s get the basics out of the way first. Most people know the "3-1-1" rule, but they don't actually know why it exists or where the loopholes are. If you’re flying in the United States, the Transportation Security Administration (TSA) mandates that all liquids, aerosols, gels, creams, and pastes must be in containers of 3.4 ounces (100 milliliters) or less. All these containers have to fit into a single, clear, quart-sized bag.
One bag per passenger. That’s it.
But here is where it gets weird. Did you know that peanut butter is considered a liquid? It is. If you try to bring a jar of Jif through security, it’s going in the trash. The same goes for salsa, jam, and even some types of soft cheese. Basically, if you can spill it, spray it, spread it, or pump it, the TSA considers it a liquid. This isn't just bureaucratic pettiness; it’s based on the physical properties of substances that could potentially be used to create explosives.
Why the carry on liquid policy is actually changing (slowly)
You might have noticed some airports don’t make you take your liquids out of your bag anymore. This isn't because they've stopped caring. It’s because of CT (Computed Tomography) scanners. These machines are massive upgrades from the old X-ray tech. They create a 3D image of your bag's contents, allowing officers to rotate the view and see through clutter.
In the UK and parts of Europe, they’ve been promising to scrap the 100ml limit entirely thanks to this tech. However, don’t get too excited. Major hubs like London Heathrow and Gatwick have hit snag after snag with the installation of these heavy machines. They actually had to push back their deadlines because the floors of the terminals literally couldn't support the weight of the new scanners without reinforcement.
So, for now, the status quo remains. If you’re flying domestic in the US or international from most major hubs, you better have that quart-sized bag ready.
The medical and baby food exceptions you need to use
Here is a detail that saves a lot of headaches: the carry on liquid policy has a very generous "necessary" clause. If you have medically necessary liquids, medications, or supplies for a baby, the 3.4-ounce limit does not apply.
This includes:
- Breast milk, formula, and juice for infants or toddlers.
- Prescription liquids like insulin or cough syrup.
- Frozen gel packs used to keep medical items or milk cold (as long as they are solid ice when you hit the X-ray).
- IV fluids.
You don't need to fit these in your tiny quart bag. You just need to tell the officer you have them. They will likely perform an additional screening—sometimes a quick swab of the bottle or a vapor test—but they won't take it away. Pro tip: keep these items in a separate small bag within your carry-on so you can pull them out quickly. It saves you from having your entire suitcase torn apart because a bottle of Pedialyte triggered an alarm.
The "Solid" workaround that savvy travelers use
If you’re tired of playing Tetris with your toiletries, the best move is to stop carrying liquids altogether. The market for solid toiletries has exploded lately. You can get high-quality shampoo bars, conditioner bars, and even solid toothpaste tabs. Since these aren't liquids, they don't count toward your limit.
I’ve seen people pack a month's worth of toiletries into a tiny corner of their bag because they switched to solids. No leaks. No mess. No "3-1-1" anxiety.
Let's talk about makeup. This is a gray area that trips up a lot of people. Eyeliner pencils? Fine. Liquid foundation? That’s a liquid. Lip balm? Usually fine, but if it’s a gloss or a very soft cream, keep it in the bag. Mascara is technically a liquid. It feels small enough to ignore, but an overzealous agent can and will flag it if your quart bag is already overflowing.
International differences are a real trap
Just because you got through JFK with a certain bag doesn't mean you’ll get through Heathrow or Tokyo Narita the same way. The carry on liquid policy is theoretically standardized by ICAO (International Civil Aviation Organization), but enforcement varies wildly.
In some European airports, they are incredibly strict about the size of the clear bag. They might even provide their own bags and force you to transfer your items. If your items don't fit in their bag, something is getting tossed. I once saw a traveler lose a brand-new bottle of expensive French perfume because the bottle was 125ml, even though it was only half full.
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That’s a crucial point: the limit is on the container size, not the amount of liquid inside. A 6-ounce bottle with only 1 ounce of lotion in it is still a violation. It’s going in the bin.
Duty-free and the "Secure Tamper-Evident Bag"
Buying liquor or perfume at the duty-free shop is the one way to bypass the 3.4-ounce rule, but it comes with a major catch. If you have a connecting flight, you have to be careful.
If you buy a bottle of gin in Mexico and fly to Atlanta, then have a connection to Chicago, you have to clear customs in Atlanta. Once you clear customs, you are outside the "secure area." When you go back through TSA for your domestic leg, that big bottle of gin is now a prohibited item... unless it’s in a Secure Tamper-Evident Bag (STEB).
The shop should provide this. It’s a clear plastic bag with a red border that shows if it’s been opened. If the seal is broken, or if you don't have the receipt visible inside the bag, the TSA will make you check it or toss it. Honestly, it’s often easier just to pack the duty-free stuff in your checked bag after you clear customs but before you re-check your luggage for the final leg.
Practical steps for your next flight
Don't wait until you're in the security line to organize. It creates stress for you and everyone behind you.
- Get a reusable TSA-approved bag. The disposable Ziplocs rip easily. A sturdy, clear TPU bag with a zipper is a great investment. It stays open on its own, making it easier to pack.
- Label your "medical" liquids. Even if it’s just contact lens solution, if it’s over 3.4 ounces, keep it separate and tell the agent upfront.
- Check your snacks. Yogurt, hummus, and creamy dips are liquids. Hard snacks like crackers or fruit are fine.
- Empty your water bottle. It sounds obvious, but it’s the #1 reason bags get pulled for manual search. Drink it or dump it before the line.
- Go solid where you can. Swap the bulky shave cream for a shave bar or a small oil.
The carry on liquid policy isn't going anywhere for the foreseeable future, at least not globally. While tech is improving, the patchwork of different scanners across the world means the safest bet is to stick to the 100ml rule. It’s annoying, sure, but being the person who holds up the line because of a jumbo-sized bottle of hairspray is worse.
Check your labels. If it says 100ml or 3.4oz, you’re golden. If it says 110ml, leave it at home or put it in your checked suitace. Simple as that.