Traveling through an airport can be stressful with so many rules about what you aren't allowed to pack, let alone what you need to remove from your carry-on at x-ray screening. One rule that sometimes trips up passengers is the Transportation Security Administration's 3-1-1 liquid restrictions. Follow these rules to be sure none of your liquids are confiscated next time you fly.

3-1-1 Liquid Rule

In their carry-on bag, passengers can bring aerosols, liquids and gels, as long as two conditions are met. First, each container can't be larger than 3.4 ounces. Second, all the containers must fit into one quart-sized, clear plastic bag with a zip top. The TSA forbids gallon bags and bags with fold-over tops.

When sending bags through the x-ray machine, most passengers are asked to remove the quart-sized bag from their luggage and put it in the bin. Passengers with TSA Precheck status can usually leave the bag of liquids in their luggage. Larger quantities of toiletries and liquids can be placed in checked-in luggage.

Exceptions are Possible

Passengers traveling with babies and small children can bring larger quantities of juice, breast milk or baby formula in their carry-on luggage. The TSA also allows passengers to bring larger quantities of prescription medication; liquids for passengers with medical conditions; medical and cosmetic items with gels or saline, such as prosthetic breasts; and frozen items as long as the item is completely frozen at the time of screening. Passengers claiming exempted items must separate them from other carry-on liquids and declare the items to airport security at the X-ray screening point.

Duty Free Items

Passengers on nonstop international flights to and from the United States can take any size containers of duty free liquid on a plane. Passengers with a connecting flight in the United States with a final destination outside the country cannot bring any duty free liquids over 3.4 oz. in their carry-on bag; this will be verified at airport security. Passengers who purchase duty-free items in the United States before traveling abroad can have their purchases placed in tamper-resistant International Civil Aviation Organization bags, which must remain sealed until they go through foreign customs. Some countries, like Japan, do not provide ICAO bags at their duty free stores.

Other Luggage Restrictions

All sharp objects, including knives and scissors, firearms and martial arts weapons must be placed in checked-in luggage. Passengers can carry on tools that are smaller than 7 inches long. Athletic equipment, including ski equipment, pool cues, baseball bats and dumbbells, must be placed in checked-in baggage. Flammable liquids are prohibited on the aircraft entirely, except for cigarette lighters, which must be in a carry-on bag, and compressed gas cartridges for life vests. Passengers should be aware that the TSA prohibits gel shoe inserts inside the cabin, as well as snow globes.