Should you put that bottle of shampoo in your checked bag, or pack it in the small bag you're taking on the plane? The Transportation Security Administration has strict rules about packing liquids in carry-on luggage. So, although you can bring liquid medications and a limited quantity of other liquid must-haves – including toiletries – onto the flight in your carry-on bag, it's almost always easiest to put liquids in a checked suitcase if possible.

The TSA Liquids Rule

The Transportation Security Administration's liquids rule is pretty simple: Excluding medications and a few other items, you're allowed one quart-size, zip-close baggie of liquids in your carry-on luggage. All containers inside that baggie must be 3.4 ounces (100 ml) or smaller, and you may be asked to remove that baggie from your carry-on luggage before going through the security checkpoint. This rule covers more than liquids with a runny consistency like water; gels, pastes, creams and aerosols are included too.

Exemptions for Liquid Medication

There are three exceptions to the TSA's limit on liquids in checked luggage. The first is liquid medication: You can bring medically necessary liquids, creams and the like through the checkpoint in quantities larger than the 3.4-ounce limit that otherwise applies. Just remove said medications from your bag and be prepared for the possibility that they may need extra screening.

Traveling With Children

If you're traveling with children, you're also allowed to bring reasonable quantities of formula, breast milk, juice and jarred food through the screening checkpoint. These liquids won't count toward your one-quart limit for general liquids, but they will be subjected to X-ray or additional screening, which may include opening the containers they're in.

Duty-Free Liquids

The final exemption for liquids in your carry-on luggage is for duty-free items that were purchased at an international airport on your way back to the United States. You can pack more than 3.4 ounces of these liquids in your carry-on, but only if they were purchased in the last 48 hours and remain in their sealed, tamper-proof packaging until you reach your final destination.

Liquids in Your Checked Luggage

As a general rule, as long as it's not flammable – and for alcohol, as long as it's not more than 140 proof – you can pack any liquid in your checked luggage. That includes full-size bottles of toiletries, duty-free alcohol or other beverages purchased abroad, and even a giant jar full of your grandmother's famous tomato soup. But nobody likes retrieving their luggage only to find shampoo, whiskey or soup all over their personal belongings. Save yourself a lot of grief by carefully packaging any liquids that go into your checked bags. Some travelers double-bag toiletries in zip-close bags for safety, while others open the bottle, put a layer of cling plastic over the opening, then replace the lid and place the whole bottle(s) in another bag for safekeeping.