Can you bring hair oil 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.

Hair oil has no pressurised can and no solid form, so the whole answer turns on how each list treats a cosmetic oil.

Korea names hair oil, the UK and Hong Kong say oils

Korea's aviation security site returns an entry for 헤어오일 (hair oil), next to a separate one for cleansing oil with the same wording. GOV.UK does not go down to the product: its liquids list has cosmetics and toiletries, including creams, lotions, oils and perfumes. Hong Kong's CAD uses nearly the same string, creams, lotions, oils, perfumes, cosmetics.

Japan's list has bath oil and aroma oil, not hair oil

The hair care row in Japan's list of restricted items gives hairspray, hair tonic, hair growth products, hair colour and bleach. Oil is printed in that cosmetics class as bath oil and as aroma oil, and the liquids list has a bath oil row as well. Hair oil is read into the class by its definition: items used to care for the body and appearance.

ANA's wording for cosmetic oils

ANA's FAQ on cosmetics lists oils with creams, lotions, sprays and gels as the cosmetics that fall under the liquid limit in carry-on baggage. Its baggage page adds 2 details for a bottle of hair oil: a container over 100 millilitres is refused even when it holds 100 millilitres or less, and 100 millilitres is read as 100 grams.

Mainland China's domestic flights: 1 bottle, opened for a check

CAAC bans liquids from carry-on on domestic flights, with an exception for cosmetics used during the trip. A cosmetic has to meet 3 conditions together: 1 item of each type, a container of no more than 100mL, and an open-bottle inspection. On international and regional flights CAAC applies the 100mL container and 1L resealable bag instead.

The 0.5 litre bottle cap is not universal

Japan counts hair oil as a toiletry in both cabin and hold, so each container is held to 0.5 L or 0.5 kg. Korea's hair oil entry gives no per-container figure for domestic flights or checked baggage. The TSA's liquids rule gives none either: it tells passengers to pack containers larger than 3.4 ounces or 100 milliliters in checked baggage.

The carry-on answer for hair oil 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 hair oil 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.