Everything that pours, sprays or spreads falls under the 3-1-1 rule in a carry-on: containers of 3.4 ounces (100 ml) or less, all in one quart size bag. Checked bags have no such limit, which is why toothpaste, shampoo and full size sunscreen usually travel in the hold.The exceptions matter more than the rule. Medication, baby formula and breast milk are exempt in reasonable quantities, duty free bottles need the sealed tamper evident bag, and alcohol has its own strength limits. Each item page below gives the carry-on and checked verdict, the quantity limit and the reason behind it.