Can you take pepper spray or bear spray on a plane?

Pepper spray and bear spray on flights in and from Japan

The rule for pepper spray and bear spray comes from the Civil Aviation Bureau's list of restricted items and is the same on domestic and international flights.

Pepper spray and bear spray: carry-on and checked baggage in Japan
Where	Allowed?	What applies
In the cabin	No	No. Bear spray, pepper spray and tear gas spray are not allowed.
In checked baggage	No	No.

Pepper spray and bear spray: no checked-bag allowance in Japan

Several countries let a small self-defence spray travel in checked baggage, but Japan's list does not, and it names bear spray first.

A row of crosses in the spray-can table: The list published by Japan's aviation bureau places bear spray, pepper spray and tear gas spray in its table of spray cans, directly under the row for cans that use no flammable or toxic gas. That row may be carried and checked. This one has a cross in both columns and no quantity.
Why putting it in a suitcase does not help: Narita Airport's FAQ explains that carry-on baggage is checked for anything usable as a weapon, and checked baggage for goods prohibited from transport. Knives and air guns fail the first test only, so they may be checked. Pepper spray is caught by the second: the liquids list puts it with paint and tyre repair sprays, which are not permitted in the cabin or in checked baggage.
Bear spray is refused even where pepper spray may be checked: The TSA allows a small container of mace or pepper spray in checked baggage, yet lists Bear spray separately with a No in both columns. CASA's forbidden entry runs pepper spray, oleoresin capsicum spray, OC spray, capsaicin spray, mace or bear spray. The European Commission's cabin list uses the wider term animal repellent sprays.

Pepper spray and bear spray: the rule country by country

The carry-on answer for pepper spray and bear spray is the same in all 7 other places we checked.

Pepper spray and bear spray: carry-on and checked baggage rules by country
Flying from	Carry-on	Checked bag	What the authority says
JapanCivil Aviation Bureau	No	No	Bear spray, pepper spray and tear gas spray are not allowed. Source
United StatesTSA	No	With limits	Carry-on: no. Checked: one 4 fl. oz. (118 ml) container of mace or pepper spray with a safety mechanism; sprays with over 2 percent tear gas (CS or CN) by mass are prohibited. Some airlines may not allow it. Bear spray is banned in both.TSA entry: Pepper Spray, Bear spray Source
European UnionEuropean Commission, EASA	No	—	Mace, pepper sprays, capsicum sprays, tear gas, acid sprays and animal repellent sprays are prohibited in cabin baggage. Source
United KingdomUK Government	No	No	Self defence or disabling sprays (for example mace and pepper spray) cannot be taken in hand luggage or in the hold. Source
South KoreaMOLIT Aviation Security 365	No	With limits	Tear gas, pepper spray and acid spray are banned from the cabin. In checked baggage, self-defence sprays are limited to 1 per person, 100ml or less. Source
Hong KongCivil Aviation Department	No	No	Mace, pepper or capsicum spray, acid sprays, animal repellent sprays and tear gas are banned from cabin baggage. Hong Kong police list tear gas with arms that are illegal to carry without a licence, in hand-carried or hold luggage. Source
Mainland ChinaCAAC	No	With limits	Mace, tear gas, pepper spray and animal repellent spray that are not state-controlled items cannot be carried on but can be checked. State-controlled items cannot be carried on or checked. Source
AustraliaHome Affairs, CASA	No	No	Pepper spray, capsicum spray, mace and bear spray are forbidden items: not permitted in carry-on or checked baggage.CASA Pack Right entry: Pepper spray, oleoresin capsicum spray, OC spray, capsaicin spray, mace or bear spray Source

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

If security in Japan will not let pepper spray and bear spray through

What to do: Pepper spray and bear spray cannot go in checked baggage either. Leave them behind or hand them to someone who is not flying. Narita Airport states that anything given up at the checkpoint is discarded and cannot be returned.
If it gets on board: Taking an item that is restricted from the cabin onto an aircraft is punishable under Japan's Civil Aeronautics Act: up to 2 years' imprisonment or a fine of up to 1,000,000 yen.

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