Low temperature burns occur when the skin is exposed to temperatures of around 40 degrees C to 50 degrees C over prolonged periods of time. This can happen during sleep, when a hot water bottle or electric warmer is in contact with the same area of skin for an extended time. Skin can be subject to burns after exposure to temperatures of 44 degrees C over periods of three to four hours, or of 46 degrees C over periods of between 30 minutes and one hour.

According to Koji Sumiyoshi, the director of Sumiyoshi Skin Clinic in Tokyo and a part-time lecturer at Juntendo University, the structure of the dermal tissue can be compromised by temperatures above a certain level even if sensory nerves do not experience sensations of pain or burning. Therefore, people should exercise caution even at temperatures that feel comfortable.

Sumiyoshi explains how low temperature burns occur: “A heating device pressed against the skin exerts pressure, and this negatively effects blood circulation.”

Normally, when skin comes into contact with a heat source, the action of the blood disperses heat throughout the rest of the body. However, when pressure is applied to blood vessels, blood circulation is hindered and heat remains concentrated. The deeper layer of skin — the dermis — which is more susceptible than it appears, can then sustain severe damage.

With normal burns, cooling the affected area with water can mitigate their severity. However, in the case of low temperature burns, such cooling “is of limited effectiveness, as the damage to the deeper layers of the skin is already done by the time one notices anything,” Sumiyoshi said. Should this occur, it is vital that you immediately go to the hospital and receive medical treatment.

Preventive Measures

The first precautionary defence against low temperature burns is to avoid using hot water bottles and similar items over long periods of time.

Akio Iketani, director of the National Institute of Technology and Evaluation, offers further advice: “When using a hot water bottle or other heating devices, don’t place them directly against your body, but rather use them to warm the bed and then remove them once you’re ready for sleep. Also make sure to switch off electric warmers.”

There have also been instances of toilet seats with heating functions causing low temperature burns when users sit on them for a prolonged period, with four such cases confirmed in 2015. In all cases, the injured were elderly people aged 80 or older.

“It’s conceivable that the elderly may fall asleep while using the bathroom, after sitting on the toilet for prolonged periods. Family members should have the temperature settings at low, or turn the heat off altogether when they know the toilet will be in use,” Iketani suggests.

Smartphones have also proven an unexpected source of low temperature burns.

According to the National Consumer Affairs Center of Japan, a woman in her 40s from Nara Prefecture reported a low temperature burn while her smartphone was charging under her arm while she slept. The Tokyo metropolitan government’s Safety and Living Section conducted an experiment where an active smartphone with a running application was wrapped in a blanket. Over a period of between 50 minutes and two hours, the temperature of the phone rose to approximately 50 C.

 “Please exercise caution when using your smartphone in bed,” said Hiromi Miyanaga, the section chief, urging greater awareness of safety issues.