Can you take mouthwash on a plane?

On a domestic flight only the quantity limits apply. On an international flight the liquid rule comes on top.

Domestic flights in Japan

The 100ml liquid limit does not apply.

International flights from Japan

Each container 100ml or less, all of them inside one transparent re-sealable bag of 1 litre or less, one bag per person.

Breath spray is listed with mouthwash. A gargle sold as a medicine falls under liquid over-the-counter medicines instead, which are excepted from the 100ml limit in the amount needed in the cabin if you declare them to the screener.

Japan's lists put an everyday mouth rinse with cosmetics, and a gargle sold as a medicine is handled by a different row.

What the Japanese lists call it

The list of restricted items files it as マウスケア用品：洗口液 (mouth-care products: mouth rinse) in its cosmetics group, which it defines as grooming products plus goods with a refreshing, fragrant, cleansing, deodorising or sanitising effect. The liquids list uses other words for the same thing: 口腔洗浄液 (oral rinse) and 口中清涼剤 (breath freshener).

Gargle is not among the named medicine examples

The exception row for prescription and over-the-counter medications gives liquid cold medicine, liquid stomach medicine and cough syrup as its Japanese examples. A gargle is not written there. For anything carried under that row, the list says the screener may ask for evidence that it is needed, such as a copy of the prescription or the pharmacy bag.

A small bottle of medicine follows the ordinary route

The Japanese list adds that a liquid or gel medicine in a container of 100 ml or less can go in the 1 litre zip bag and be carried on like any other liquid, with nothing to say to the screener. At that size a medicated gargle and a cosmetic mouthwash pass the checkpoint in the same way.

South Korea's entry is for a gargle solution

South Korea's searchable list has no general mouthwash entry in our copy. It lists a gargle solution (헥사메딘 가글액) under the cabin liquids control and says that for a medicine the passenger shows a prescription or similar proof to the security officer, who may allow the amount needed during the flight.

The carry-on answer for mouthwash is the same in all 8 other places we checked. The limits themselves are not identical, so read the row for the country you fly from.

Each row comes from that authority's own page. Airlines can be stricter, and the screening officer has the final say.

What to do

Move mouthwash to the bag you check in before you reach security, within the checked-baggage limits above. Narita Airport states that anything given up at the checkpoint is discarded and cannot be returned.