As we mentioned, it’s unusual for TENS to result in actual physical damage, even when it is applied repeatedly over the course of the day and during any number of days in a row. However, there are some individuals who should not engage in this or any type of electrical stimulation without first consulting with their doctor, including:
People with a pacemaker - It is likely that any type of electric therapy device will present problems for people with pacemakers. While there are some pacemakers on the market today that are not affected by such devices, they are still relatively small in number. Therefore, you should never use this or any EMS device if you have a pacemaker unless specifically cleared to do so by your doctor.
Pregnant women - While the TENS device itself should present no threat whatsoever to the health of pregnant women, there have not been sufficient scientific studies conducted to be able to state with confidence that it poses no threat to the developing fetus. Therefore, the safe route is the right route and pregnant women should not use any type of EMS device.
Those with epilepsy - Epilepsy is a neurological condition related to the way electrical impulses are processed by the brain. Therefore, many doctors believe it is theoretically possible that engaging in electrical muscle stimulation could somehow initiate an epileptic seizure. It should be emphasized that there is at this time no conclusive evidence that this would occur. But neither is there conclusive evidence that it would not.
Lymphedema - Lymphedema is the result of a compromised lymphatic system and results in localized fluid retention in those affected. It’s thought that TENS treatment may aggravate lymphedema and perhaps result in ever greater amounts of fluid retention. Therefore those with lymphedema are advised to avoid electrical muscle stimulation machines.