Generally:
* TSA (Transportation Security Administration - in the US) allows: Aerosol hair mousse in your carry-on if it's in a container that is 3.4 ounces (100 milliliters) or less. The container must also fit in a single, quart-sized, clear, plastic, zip-top bag.
* Larger Aerosols Must Be Checked: If your aerosol hair mousse is larger than 3.4 ounces, it must be placed in your checked baggage.
Important Considerations:
* Airline Regulations: Always check the specific airline's website for their rules regarding aerosols and carry-on items. Some airlines may have stricter rules than the TSA.
* International Flights: Regulations vary significantly from country to country. Check the rules of the country you are departing from and arriving in. Some countries may prohibit aerosols in carry-on luggage altogether.
* "Travel-Sized" Products: Look for hair mousse specifically labeled as "travel-sized." These are usually compliant with the 3.4-ounce rule.
* Confiscation: If your aerosol hair mousse does not meet the size requirements, it will likely be confiscated at the security checkpoint.
In Summary:
If your aerosol hair mousse is 3.4 ounces (100 ml) or less and fits in your quart-sized bag, you can likely carry it on. If it's larger, pack it in your checked baggage. Always check with your airline and the relevant authorities in the countries you're traveling to.