Electric blankets keep the bed warm before you get in and while you are sleeping. Electric blankets are not bad for you per se, but heating blankets are not meant for use with certain medical conditions or electrical hazard concerns. Safe operation is important for safety and health reasons.
Electromagnetic fields concern some doctors. Electrical fields surround any wire with electrical current traveling through it. Although the blankets must pass the safety standards, electromagnetic fields are a concern for pregnant women and people with pacemakers. Ask you doctor if there is a risk when using a heating blanket during pregnancy or if you have a pacemaker. Manufacturers do make low-voltage electric blankets that have a power converter that changes the AC to DC for people concerned about electromagnetic fields.
Electric blankets are not recommended for use on infant and small children's beds. Blankets operate on electrical current and can cause electrical shock if the infant or child would wet the bed or spill liquid on the blanket. Infants can't tell you if the blanket is too warm on the skin.
People who cannot move or with poor circulation should not use the electric blanket. Paraplegics, quadriplegics and those who are incapacitated can suffer burns. Diabetics may have loss of sensation in their limbs, which prevents them from feeling if the blanket is too warm.
People should not use the electric blanket on a bed if they don't know how to operate the controls or understand how a heating blanket works. According to Sunbeam and Perfect Fit Industries, only people that can operate the heating control and know how the blanket works should use their product.