Electric blankets use grids of thin, insulated wires to generate heat internally. Earlier ones used adjustable thermostats to control temperature, but modern blankets (after 1984) use rheostats. Rheostats not only measure the heat generated by the blanket, but the body heat generated by the user as well. This results in a more even heating and fewer hot spots.
The history of these blankets is a little murky. When electricity was first introduced into households around the 1900s, would-be inventors added an electrical element to many common items. The first electric blankets were bulky and extremely dangerous. Most people saw them as curiosities, not legitimate consumer products. Few examples of early ones exist intact.
It wasn't until the 1920s that electric blankets became appealing to the general public. Tuberculosis patients would spend much of their recovery time outdoors in the fresh air, but the temperatures would drop overnight. Nurses began using these blankets to keep their patients warm while they remained outside. Eventually they made their way into the consumer market.
Electric blankets were actually more popular in the 1970s and 1980s, especially among the elderly and people with lower incomes. One thin one could take the place of several expensive cover sheets, insulating blankets and comforters. They could be placed on wheelchairs for added comfort. A hot-natured sleeper could adjust his blanket temperature without affecting his cold-natured spouse. Manufacturers touted many benefits of the blankets, but one serious drawback remained.
Because the wires embedded in electric blankets are powered by electricity, there has always been a risk of shock or fire. Manufacturers routinely warn against misuse of the blankets, but consumers themselves cannot always detect compromised wiring. The continued use of older blankets has lead to significant problems with accidental fires and electrocutions. Many of the most dangerous models have already been recalled, but some elderly or low-income consumers continue to use the thermostat-controlled models sold in the 1980s.
There have also been suggestions that long-term exposure to electrical fields can lead to the development of cancer. Research in this area is still ongoing, but proponents of a cancer-free lifestyle suggest limiting the use of electric blankets. Alternatives do exist, including the use of heated waterbeds or modern insulated blankets that retain much more body heat. Consumers who do want to buy a newer model should look for a generous power cord length, an adjustable rheostat controller separate from the blanket, and detailed safety instructions. Those sold at thrift stores, flea markets and yard sales may be too old for safe usage.