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What is a TENS Unit? + How to Use & How Does it Work

Written by Joe Cohen, BS | Last updated:
Jonathan Ritter
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology) | Written by Joe Cohen, BS | Last updated:

A TENS unit is a device that stimulates nerves throughout the body by applying an electrical current through the skin. People use these devices to relieve pain: but do they work? What is the theory behind them? Read on to find out!

What is TENS?

TENS unit

Figure 1 Source: http://www.therxreview.com/tens-unit-what-it-is-and-what-it-does/

TENS is short for transcutaneous electrical nerve stimulation. It is generally considered a safe (when used correctly), inexpensive, and non-invasive method of stimulating nerves by applying electricity to the surface of the skin.

Because it can be used to stimulate almost any nerve in the body, TENS has a very diverse range of uses. One of the most common uses of TENS is to reduce chronic pain throughout the body. Other people use it to help with psychological disorders, improve lung function, and potentially enhance athletic performance.

Because it is a relatively recent technology, new uses for TENS are constantly being developed and discovered.

However, not all studies find that TENS is effective, and the results can be quite inconsistent across different studies. One possible reason for this is that TENS treatment may be very susceptible to the placebo effect.

Unfortunately, many of the early studies on TENS were not placebo-controlled, which can make it difficult to draw firm conclusions.

Therefore, we encourage healthy skepticism when looking at any particular health claim about TENS.

TENS (transcutaneous electrical nerve stimulation) units stimulate the nerves by applying electricity to the skin. People use them to relieve pain, but the evidence of their effectiveness is fairly low.

FDA Regulation

TENS units have not been approved by the FDA for any medical purpose or health claim. Talk to your doctor before using TENS.

TENS devices are classified as Class II devices. They can be approved as “adjunct in the treatment of pain” as long as they are similar enough — that is, at last as safe and effective — to already cleared TENS devices on the market.

How It Works

It’s not actually known for certain how TENS might work, although a few prominent theories claim to explain at least some of its effects.

The most common explanation of how TENS works for pain relief involves the “gate control” theory of pain. The basic idea is that stimulating large areas of the skin may shut off or suppress the nervous system in the upper part of the spinal cord. Closing this “gate” may prevent pain signals from passing to the brain from the rest of the body [1].

Reduced pain may cause the body to release natural (“endogenous”) opioids or the body’s “natural painkillers” — according to another explanation [1].

Repeated use of a TENS unit may also lead to gradual changes in the nearby muscles which allows them to relax more easily, which could lead to decreased sensations of pain in those muscles [2].

Some researchers speculate that TENS units might work by closing the “gate” that passes pain signals between the brain and body, but this has not been meaningfully backed up with evidence.

Variations and Techniques

Although the way that TENS is used can be very flexible and is often tailored to the individual users’ needs, there are a few popular variations referred to by specific names.

The most common is Acu-TENS, which means that the TENS stimulation pads are placed on specific acupuncture points [3].

There is also a technique called “tVNS”, which stands for transcutaneous vagus nerve stimulation. This is a method of connecting a TENS unit to specific parts of the ear in order to stimulate the vagus nerve. Despite the lack of proper clinical evidence, people most commonly use it for mental or psychological conditions (such as depression) [4, 5].

There are also some other devices that are similar to TENS. For example, an interferential currents (IFC) unit works similarly, although its electrical stimulation is stronger and can penetrate deeper into muscles. One study suggested that both TENS and IFC units are effective and do not differ much in their ability to relieve lower back pain. Not many studies have directly compared the effectiveness between the two [6].

Another technique, called electroacupuncture (EA), uses small acupuncture needles to deliver electrical stimulation instead of pads. One study found that EA was more effective than TENS for relieving lower back pain, although this may be because its stimulation is more direct and invasive. Larger trials are lacking. EA is quite impractical for home use, though, as it requires a trained professional to apply [7].

Several varieties of TENS units exist, such as Acu-TENS, tVNS (transcutaneous vagus nerve stimulation), IFC (interferential currents), and EA (electroacupuncture).

How TENS Units Are Used

Although there are many different types of TENS units, most of them share the same basic features.

TENS unit

The first thing you should do is to become familiar with the particular TENS machine you have, and how you can control the settings.

Most TENS units will have two main controls: one to adjust how fast or slow the electronic signals are (generally measured in pulses per second, or “ppm”), while another control will adjust the strength of the electrical stimulation itself. (Note that you should always start with both of these knobs turned all the way off before you turn on the machine!)

Next, you should prepare your skin for the TENS unit by cleaning the area with soap and water, or a small amount of rubbing alcohol.

After your skin has completely dried off, take the stimulation pads from the unit and place them around the area you want to stimulate (for example, wherever your pain is). Slowly turn up and adjust the dials to find the stimulation pattern that you find works the best. Note that if it is applied properly, the TENS treatment itself should not be painful.

There are many different strategies for how and where to place the electrodes on your body. The effectiveness of the TENS may depend on the placement of the pads, so TENS users should experiment and consult a medical expert to find out what might work best for their particular symptoms.

However, one solid rule is to make sure that the pads are not touching each other — at least 1 inch apart is the generally-accepted minimum amount of space between them [8].

TENS unit pads are applied directly to clean skin. A medical expert can help determine the correct placement of the electrodes.


The effects of TENS treatment seem to be dose-dependent, meaning that the benefits people receive may depend on the frequency and intensity that is used.

However, the optimal stimulation levels might be different depending on the specific condition you are using TENS for. For example, a review of 43 TENS studies found that “moderate” levels of TENS (medium frequency and strength of electrical stimulation) was effective for reducing muscle pain, but that other types of pain may benefit from more intense stimulation levels [9].

Because each condition is different, it is not possible to recommend any particular set of TENS unit settings. However, researchers have noted TENS is much more likely to have positive results when patients carefully follow the instructions that their medical experts give them [10].

In clinical research, the effectiveness of TENS appears to depend on the frequency and intensity of treatment. It’s very important to carefully follow all instructions from a medical professional.

Side Effects and Limitations

TENS is considered to be safe when properly used.

The vast majority of participants in the many TENS studies that have been done reported no adverse side-effects.

One of the only reported negative effects is minor skin irritation at the placement of the electrodes, as well as possible pain when removing the electrode pads [11].

Limitations and Caveats

The way in which TENS units are used can make it difficult to draw solid conclusions from many studies.

Most of the time, TENS is administered not by a medical professional, but by the patients themselves in their own home — therefore, the way they use their TENS unit may be inconsistent, and it can be difficult to verify whether all the patients in a given study followed the procedures correctly or in the same way. Some research has shown that few patients follow the recommendations perfectly, and therefore may not achieve the maximum desired results.

This means that caution should be used when trying to draw conclusions from any single TENS study, as the results may not be entirely reliable [12, 13, 14].

Another problem is that one of the most common uses of TENS is to treat pain — but pain can be highly subjective and difficult to measure precisely (quantitatively).

Relatedly, it is also very difficult to know how much of TENS’ effects might be due to the placebo effect. Many of the early studies done on the TENS unit did not use a placebo group, and at least one large placebo-controlled study has reported no significant differences between the effects of TENS treatment and the effects of a placebo.

Similarly, a large-scale review of many different TENS studies came to the conclusion that they could not confirm for certain that the TENS unit was any more effective than a placebo for treating osteoarthritis pain. In light of these issues, any study that is not placebo-controlled should be looked at with some skepticism until further research confirms their results [11, 1, 15].

We strongly recommend caution when trying to draw conclusions from any single study on TENS units. Be aware that the placebo effect likely played a role in positive results.


Because it involves running (low levels of) electricity through the body, there is a small chance that the TENS unit could interfere with an implanted device, such as a pacemaker. Although the studies on this are unclear, it would be wise to use caution and consult a doctor before using TENS if you have a pacemaker [16].

User Experiences

The opinions expressed in this section are solely those of the users who may or may not have medical or scientific training. Their reviews do not represent the opinions of SelfHacked. SelfHacked does not endorse any specific product, service, or treatment.

Do not consider user experiences as medical advice. Never delay or disregard seeking professional medical advice from your doctor or another qualified healthcare provider because of something you have read on SelfHacked. We understand that reading individual, real-life experiences can be a helpful resource, but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified healthcare provider.

There are many different TENS units you can purchase, and they are sometimes even covered by some insurance programs.

TENS units also vary considerably in size and strength — therefore, keep in mind that these user experiences may be specific to the particular TENS unit and setting that each person used.

Most people also say that their TENS unit is easy to set up and learn how to do yourself, as most of the machines are designed to be as straightforward as possible.

Some users report a reduction in back pain, which seems to be one of the most common home uses of this product. Other users have said that using it has helped them to manage their pain after surgery. There are other reports of users saying it was incredible for keeping their headaches at bay.

Some of the main complaints include that the pads of some machines are either too sticky or not sticky enough, which can make them somewhat difficult to set up properly. Additionally, as with any electronic product, there are always reports of units breaking or not working properly after some time – so it may pay off, in the long run, to invest in a relatively higher-quality unit if you plan on using it regularly for an extended period of time.

Finally, many users have noted that the feeling of the electricity on your skin can be strange at first, and can take a while to get used to. A few users have even said that they were never quite able to get used to the strange feeling of it, and therefore did not decide to keep using their TENS unit.


A TENS unit is a device that stimulates nerves throughout the body by applying an electrical current through the skin. It is most commonly used to relieve pain, though the evidence of any benefit is of relatively low quality due to a lack of well-controlled studies.

Some researchers speculate that TENS units might work by closing the “gate” that passes pain signals between the brain and body, but this has not been meaningfully backed up with evidence. Several varieties of TENS units exist, such as Acu-TENS, tVNS (transcutaneous vagus nerve stimulation), IFC (interferential currents), and EA (electroacupuncture).

The effectiveness of TENS units may be strongly dependent on the frequency and intensity of application. We strongly recommend following any instructions given by a medical professional.

Further Reading

About the Author

Joe Cohen, BS

Joe Cohen, BS

Joe Cohen flipped the script on conventional and alternative medicine…and it worked. Growing up, he suffered from inflammation, brain fog, fatigue, digestive problems, insomnia, anxiety, and other issues that were poorly understood in traditional healthcare. Frustrated by the lack of good information and tools, Joe decided to embark on a learning journey to decode his DNA and track his biomarkers in search of better health. Through this personalized approach, he discovered his genetic weaknesses and was able to optimize his health 10X better than he ever thought was possible. Based on his own health success, he went on to found SelfDecode, the world’s first direct-to-consumer DNA analyzer & precision health tool that utilizes AI-driven polygenic risk scoring to produce accurate insights and health recommendations. Today, SelfDecode has helped over 100,000 people understand how to get healthier using their DNA and labs.
Joe is a thriving entrepreneur, with a mission of empowering people to take advantage of the precision health revolution and uncover insights from their DNA and biomarkers so that we can all feel great all of the time.


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