[ TIPS · THE DISPATCH ]

The Carry-On Liquids Rule Has a Loophole Most Travelers Miss

The 3-1-1 rule isn't the whole story. Medical liquids, solid toiletry swaps, and duty-free sealed bags are all TSA-approved ways to carry more than 3.4 oz in your carry-on — and most travelers have no idea.

I spent three years flying carry-on only before I realised I’d been playing by rules that were stricter than the actual rules. I was wedging shampoo into tiny bottles, decanting my face wash into a 1 oz container that dispensed approximately four drops per pump, and leaving my big jar of prescription moisturiser at home entirely. All because I thought 3.4 oz was the hard ceiling. It’s not.

The TSA’s 3-1-1 rule is real, but it has three legitimate exceptions that are written into official policy and are widely ignored — either because the TSA website buries them, or because travelers assume the worst when they see a uniformed agent. Let me walk you through each one, exactly how to use it, and where the actual limits are.

This is the one that genuinely changes the game for a lot of people. Per TSA policy, “medically necessary liquids, gels, and aerosols” are exempt from both the 3.4 oz limit and the quart-sized bag requirement. That’s not a grey area — it’s stated clearly on the TSA website and has been policy since before I started traveling seriously.

What counts as medically necessary:

• Prescription medications in liquid form (insulin, liquid antibiotics, cough syrup with a script)
• Over-the-counter items you can reasonably argue are medical — contact lens solution, saline nasal spray, eye drops
• Baby formula, breast milk, and juice for infants or toddlers (this one has essentially no volume limit)
• Gel ice packs used to keep medications cold

You do not need a doctor’s note. You do not need to show a prescription label (though having one helps if an agent questions you). You simply need to declare the items separately at the checkpoint, pull them out of your bag before it goes through the scanner, and tell the agent what they are. They may swab the containers for explosive residue — that’s normal, takes 45 seconds, and does not mean they think you’re suspicious.

I carry a large bottle of prescription-strength hydrocortisone cream (it’s a gel, it counts) and a full-size contact lens solution without batting an eye. The one time an agent stopped me, I said “prescription gel and saline, I’ve declared them” and was through in under a minute.

Three years ago I would have told you solid shampoo bars were punishment. They left my hair feeling like straw, they dissolved in the shower tray, and the good ones cost £18. That’s changed significantly.

Solid toiletry alternatives that are genuinely worth using in 2026:

• Shampoo bars: Ethique’s Pinkalicious (around $16, lasts 3–4 months of regular use) and Lush’s Honey I Washed My Hair ($14) actually produce lather and don’t wreck color-treated hair. I’ve tested both extensively.
• Toothpaste tablets: Bite and Unpaste are the brands worth trying. They’re slightly gritty at first, but you adapt in two days. A tin of 62 tablets ($12) covers a three-week trip.
• Solid sunscreen: EltaMD makes a solid SPF 30 stick ($28) that’s legitimately good for face and shoulders. It’s not a substitute for body coverage on a beach day, but it handles incidental sun on a city trip.
• Solid face wash: CeraVe Hydrating Cream-to-Foam cleanser comes in a solid bar format now. For a trip through Japan — where you’re washing your face twice a day — this is my go-to. (Speaking of Japan, if you’re planning a longer rail journey, my piece on six days through Japan’s countryside from Kanazawa to Hakone covers what to actually pack for that kind of trip.)

None of these count as liquids, gels, or aerosols. They go in your bag with your socks. No quart bag, no size limit.

The honest trade-off: you’ll spend 20–30 more dollars up front than you would on travel-size liquids. But you’ll stop throwing away half-empty bottles at the airport, and you’ll get through security faster. I’ve done the math — it’s worth it after your second trip.

This one is technically correct but has a lot of nuance that people either don’t know or get wrong, resulting in confiscated whisky at a connection.

The rule: liquids purchased at duty-free shops past the security checkpoint can be carried in your carry-on, regardless of volume, if they are in a sealed, tamper-evident Security Tamper-Evident Bag (STEB) with the receipt visible inside the bag. The bag must not be opened or tampered with.

This works on direct flights with essentially no drama. You buy a litre of Hendrick’s at the Amsterdam airport duty-free, it goes in a sealed bag at the register, you board, done.

Where it gets complicated: international connections through the US. If you’re flying Amsterdam → Chicago → Los Angeles, you’ll clear US Customs in Chicago and go back through TSA security. At that point, TSA does not recognise the international STEB as an automatic pass. They can and do confiscate it. The exception is if you have a same-day connecting flight that’s under a certain time threshold and the STEB was issued within 24 hours — but enforcement is inconsistent enough that I wouldn’t stake a $60 bottle of olive oil on it.

My practical rule: duty-free sealed bags are safe on direct flights and on itineraries where your connection is in the same country as your departure. For US connections from international origin, either check a bag for the duty-free purchase or drink the wine in the lounge.

For a two-week trip, my liquids quart bag now has room to breathe because I’ve moved most things to solids or medical exemptions. Here’s the breakdown:

In the quart bag (3.4 oz or under):

• Perfume sample vials (free from department store counters, honestly)
• A small tube of lip balm with SPF
• Travel-size dry shampoo aerosol (the one thing I haven’t replaced)

Declared separately as medical:

• Full-size contact lens solution (360 ml)
• Prescription eye drops
• Saline nasal spray (this one I use proactively on long-haul flights — cabin air is brutal)

No bag needed (solids):

• Shampoo bar, conditioner bar, solid face wash, toothpaste tablets, solid sunscreen stick

The result is I have 80 percent of my quart bag free for things I actually need in liquid form, and I’m not hunting for a pharmacy in Lisbon at 10pm because I ran out of contact solution. (If you’re heading to Lisbon long-term, I wrote about where to stay when you’re remote-working for a month — the neighbourhood you pick affects everything from your morning commute to your grocery run.)

It happens. Most TSA agents know policy well, but you’ll occasionally hit someone who doesn’t know the medical exemption or who misreads a solid product as a gel. Stay calm, state what you know (“TSA policy allows medically necessary liquids above 3.4 oz when declared”), and ask to speak with a supervisor if needed. You can also file a complaint with TSASupport on Twitter/X — they’re responsive and will correct agents who are enforcing non-existent rules.

The TSA’s own website (tsa.gov) is the source of truth. Screenshot the relevant policy page before a trip if you’re carrying anything unusual. Having it on your phone takes five seconds and wins arguments.

For more packing strategy across different trip types, the itineraries section has destination-specific breakdowns including gear recommendations. And if you’re traveling solo, especially as a woman, the piece on genuinely safe solo female destinations in Latin America in 2026 covers security logistics beyond just airport security.

The 3-1-1 rule is real. It’s just not the whole rule, and alot of smart travelers treat it like it is.

Know the exceptions, use them confidently, and stop leaving your full-size moisturiser at home.

This article contains affiliate links marked rel="sponsored". We may earn a commission at no extra cost to you.