The TSA limits carry-on liquids, aerosols, and gels to 3.4 ounces (100 mL) as a security measure against potential threats. This rule, known as the 3-1-1 liquids rule, was implemented in response to a foiled terrorist plot in 2006 involving liquid explosives. By limiting the quantity of liquids, aerosols, and gels passengers can bring in their carry-on luggage, the TSA aims to minimize the risk of someone using these substances to create an explosive device or cause harm on board an aircraft.

The 3-1-1 liquids rule requires that any liquids, aerosols, and gels passengers carry on board must be in containers no larger than 3.4 ounces (100 mL) and placed in a single, quart-sized, clear plastic bag. This approach allows security personnel to quickly and efficiently screen these items during the airport security checkpoint process, ensuring the safety of all passengers and crew members.