The most common side effect with electrotherapy is skin irritation or rash, caused by the adhesives in the electrodes or the tape holding the electrodes in place. Overusing electrotherapy may cause a burning feeling in the skin. Directions about the duration of therapy should be followed closely to avoid a problem.
Electrical stimulation should not be applied over malignancies or areas with broken skin or an infection. Bruising, bleeding, or infections are possible with the types of electrotherapy that penetrate the skin.
Placing the pads over the heart or over pacemaker leads could cause cardiac arrhythmia and placing them over a pregnant woman's abdomen could cause fetal damage. In fact, people with pacemakers and pregnant women are generally advised to avoid electrotherapy altogether.
Placing the pads over the throat could cause low blood pressure. Using electrotherapy while driving is not recommended.