The Basic Rule: Liquids, Gels, and Aerosols Are Restricted

Most airlines follow the 3-1-1 rule for liquids: containers of 3.4 ounces (100 milliliters) or smaller, all fitting into one quart-sized clear plastic bag, one bag per passenger. This applies to anything that flows, spreads, or sprays—including shampoo, toothpaste, peanut butter, yogurt, and deodorant. The rule exists because the Transportation Security Administration (TSA) and equivalent agencies in other countries treat these items as potential security risks during flight.

Solid items—even if they feel like they could be liquid—usually pass through. A bar of soap, a stick of deodorant, or a solid perfume are fine. But the moment something is creamy, pasty, or in a spray bottle, it counts as a liquid or gel and must follow the 3-1-1 rule. If you are unsure about a specific item, the TSA website has a "What Can I Bring?" tool where you can search by name.

Key Takeaways

  • Liquids, gels, and aerosols must be 3.4 ounces or smaller and fit in one clear quart-sized bag per person.
  • Sharp objects like knives, box cutters, and razors are prohibited in carry-on bags but allowed in checked luggage.
  • Electronics larger than a laptop (like a full-sized gaming console) may be screened separately but are usually allowed.
  • Medications in their original labeled containers are permitted, and you do not need to declare them unless they contain restricted substances.
  • Rules vary slightly by airline and country, so check your specific carrier's website before packing.

Items That Are Always Prohibited in Carry-On Bags

Weapons and sharp objects are the main category. This includes knives of any length, box cutters, razors, scissors with blades longer than 4 inches, and ice picks. Firearms, ammunition, and explosives are also banned. Tools like hammers, wrenches, and screwdrivers are prohibited because they can be used as weapons, though some airlines allow small multi-tools if the blade is under 2.36 inches.

Sporting equipment with a sharp edge or point—such as ski poles, spear guns, or martial arts weapons—cannot go in your carry-on. Flammable items like lighter fluid, paint thinner, and certain types of batteries are restricted. Self-defense sprays like pepper spray and mace are prohibited on most airlines, though some allow them in checked bags under specific conditions.

If you need any of these items at your destination, pack them in your checked luggage instead. Checked bags have different rules: many items banned from carry-on are permitted below deck because the cargo hold is not pressurized the same way and passengers cannot access it during flight.

Electronics and Batteries: What Fits in Your Bag

Laptops, tablets, phones, and cameras are allowed and do not count toward your liquid limit. You will need to remove your laptop from your bag during security screening, so pack it where you can reach it easily. Larger electronics like gaming consoles, portable projectors, or external hard drives are permitted but may be screened separately—just be prepared to open your bag if asked.

Batteries have specific rules. Standard AA, AAA, and 9-volt batteries in your carry-on are fine. Lithium batteries—the rechargeable kind in phones and laptops—are allowed as long as they are installed in a device. Spare lithium batteries (not in a device) are restricted on most airlines; if you need spares, check with your carrier first, as some allow them in limited quantities while others prohibit them entirely in carry-on.

Power banks and portable chargers are allowed as long as they are under 100 watt-hours. Larger power banks may be prohibited or require airline approval. If you are traveling with expensive or fragile electronics, carrying them on rather than checking them is usually safer because you control how they are handled.

Medications, Food, and Personal Care Items

Prescription and over-the-counter medications in their original labeled containers are permitted in carry-on bags. You do not need to declare them to security unless they contain controlled substances. If your medication is a liquid (like insulin or cough syrup), it is exempt from the 3-1-1 rule—you can bring more than 3.4 ounces, but you should declare it at security and be prepared to show the label.

Solid foods like sandwiches, fruit, cookies, and cheese are allowed. Peanut butter, jam, honey, and other spreads count as liquids or gels and must follow the 3-1-1 rule. Yogurt, pudding, and ice cream are also restricted. Alcohol in your carry-on is prohibited, though you can purchase it after security and bring it on the plane in some cases (rules vary by airline and destination).

Toiletries like toothpaste, shampoo, lotion, and sunscreen must be 3.4 ounces or smaller. Solid deodorant, bar soap, and solid perfume do not count as liquids. Razors with disposable cartridges are prohibited, but electric razors are usually allowed. If you wear contact lenses, solution counts as a liquid and must follow the 3-1-1 rule.

Items That Depend on Your Airline or Destination

Some items fall into a gray area where rules differ by carrier or country. Lighters are prohibited on most U.S. airlines, but some international carriers allow one lighter in your carry-on. Vaping devices and e-cigarettes are allowed by many airlines but prohibited by others; check before you pack. Certain types of batteries and power tools may be permitted by one airline and banned by another.

If you are traveling internationally, your destination country may have stricter rules than your departure airport. For example, some countries prohibit certain types of sporting equipment or tools that would be fine in the United States. The safest approach is to check both your airline's website and the rules of your destination country before packing anything you are uncertain about.

Some items require advance notice. If you are traveling with a large musical instrument, a mobility device, or medical equipment, contact your airline ahead of time. They may need to arrange special handling or seating, and knowing the rules in advance prevents delays at the airport.

How to Pack Efficiently Within the Rules

Start by placing your liquids bag at the top of your carry-on where you can pull it out quickly at security. Keep your laptop and large electronics accessible—you will need to remove them. Pack heavier items at the bottom and lighter items on top to prevent crushing fragile goods.

Use small containers or travel-sized bottles for liquids whenever possible. Many drugstores sell empty bottles in the 3.4-ounce size, and you can fill them with your own products. This saves space and ensures you stay within the limit. If you are unsure whether an item is a liquid, err on the side of caution and pack it in your liquids bag.

Wear slip-on shoes to security so you can remove them quickly. Keep your ID and boarding pass easily accessible. If you are traveling with medications, keep them in their original containers and place them where you can show them if asked. These small steps make the security process faster and reduce the chance of delays.

Frequently Asked Questions

Can I bring a full-size bottle of perfume if I buy it at the airport after security?

Yes. Once you pass through security, you can purchase full-size liquids at airport shops and bring them on the plane. The restriction applies only to items you bring from home or pack before security screening. Keep your receipt in case you need to show it.

Are gel insoles or gel eye masks allowed in carry-on?

Gel insoles and cooling gel masks are usually allowed because they are not considered liquids—they are solid gels. However, if they leak or feel like they could spill, pack them in your liquids bag to be safe. When in doubt, ask a security officer before you go through the line.

What if I forget my medications at home and need to buy them at my destination?

You can purchase over-the-counter medications at pharmacies and drugstores at your destination. For prescription medications, you will need to contact a local pharmacy or doctor. Some medications available by prescription in one country require a prescription in another, so research ahead if you are traveling internationally.

Can I bring a lighter or matches for camping?

Lighters and matches are prohibited in carry-on bags on most airlines. If you need them for camping, pack them in your checked luggage—but check your specific airline first, as some prohibit them in checked bags too. Buying them at your destination is often easier than trying to transport them.

Do I need to remove my phone and headphones from my bag at security?

No. Phones, headphones, and small electronics can stay in your bag. You only need to remove laptops and larger electronics. Removing your liquids bag and placing your ID and boarding pass on top of your bag will speed up the screening process.