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Kairo pocket warmers are an extremely useful and cheap method to keep your hands warm in winter. This article explains how pocket warmers work and introduces popular types that can be found at supermarkets and convenience stores.
Kairo is the name for small sachets containing heat-generating liquid or powder that one can carry around to stay warm.
Photo by pang yu liu
When looking back on the history of kairo, people kept warm in the 17th and 18th centuries by heating stones, sand or salt, then wrapping them in cloth and putting the bundles in their chest pockets of their clothing. Around the same time, ash-type kairo, made of charcoal and wood ash mixed together and placed in a metal vessel, appeared on the market.
In the twentieth century, hakukin kairo was invented, which utilized the scientific reaction between platinum metal and the flammable liquid benzene. It had to be wrapped up in cloth when used, or it would get too hot. Hakukin kairo products from many companies appeared on the market, and in a flash, the use of kairo became routine.
Since 1975, disposable kairo, which are now the most commonly used type of kairo, have progressively become more and more advanced. This kairo comes in a special film that prevents exposure to air. When opened, it is designed so a chemical reaction with the air occurs and the kairo heats up.
There are several types of disposable kairo. Some are designed to be stuck to a layer of clothing or carried in a pocket, and still others are made specifically for feet. A kairo's heat will reach a temperature of 50°C to 68°C (122°F to 154°F); the sticky variety retains this heat for 12 to 14 hours, while the non-sticky variety lasts for 18 to 20 hours. In the winter, kairos are very convenient when going outdoors.
You can use sticky-type disposable kairo to warm up a particularly cold spot on your body, and they are quite convenient. It is said that warming up the sacrum (the bone located at the base of the spine, slightly above the buttocks) is an effective way to relieve pain symptoms like backaches and menstrual cramps. Give it a try yourself.
Attach the sticky side to your clothing. After five minutes, the kairo will heat up. Take care not to stick kairo directly onto your skin, or on a place where it could touch your skin! It could result in first-degree burns. Once the kairo loses its heat, quickly remove it from your clothing. The more time passes, the more difficult it will be to remove.
Activate the non-sticky variety of kairo by removing it from its bag and giving it a vigorous shake. Once the contents mix together, the kairo will heat up.
Japanese winters are extremely cold, but you can overcome the chill of the season with this helpful trick. Whenever you think it's too cold to bear, drop by a drugstore or convenience store and pick up a disposable kairo.