For years, travelers have become accustomed to meticulously packing liquids ranging from shampoo to sunscreen in their carry-on bags in order to meet the TSA liquid limit—and avoid getting that expensive perfume confiscated.

Internationally, this rule is known as “3-1-1." Liquids, gels, and creams packed in a carry-on must be in containers no larger than 3.4 ounces (100 mL). All containers must fit in a single, clear, quart-sized bag. (Larger liquids can still be brought along on your travels but must be packed in checked luggage .)

While commonly referred to as “liquids,” these regulated substances are technically known as LAGs , an abbreviation for liquids, aerosols, and gels.…