The listed below are dangerous items which are not permitted to send by international mail. For details, please see "Nonmailable Articles in International Mail" on the website of Japan Post Service.
Flares, Fuses, Fireworks etc.
Flammable aerosols, Camping gas, Butane gas etc.
Compressed oxygen, Liquid nitrogen, Spray, Fire extinguishers, Diving Tanks etc.
Liquid Ammonia, Carbon monoxide Oxidized ethylene etc.
Perfume, Manicure, Paint, Alcohol, Oil lighter, Adhesives, Ink, Heating oil, Thinner, Gasoline etc.
Matches, Sulfur, Metallic powder, Phosphorus, Celluloid etc.
Substances liable to spontaneous combustion
Charcsoal, Sodium sulfide, Metallic catalysts
Substances which in contact with water emit flammable gases
Calcium, Magnesium, Barium etc.
Oxygen generator chemical, Hydrogen peroxide solution, Ammonium nitrate fertilizer, Bleaching powder etc.
Curing agents etc.
Toxic and Infectious Substances
Insecticides, Agricultural chemicals, Antiseptics, Mercury compounds etc.
Bacteria, Viruses, Waste medical supplies etc.
Radium, Cesium, Plutonium, Uranium etc.
Mercury, Sulfuric acid, Hydrochloric acid, Acetic acid, Sodium hydrate, Potassium hydrate, Wet battery etc.
Miscellaneous Dangerous Goods
Magnetized materials, Dry ice etc.
To find more details, check the information by Japan Post