What Does a TENS Machine Do?

The Short Answer –

A Transcutaneous Electrical Nerve Stimulation Machine (commonly known as a TENS unit) is a battery operated device that uses pads to transmit small electrical pulses to areas of pain with the aim of providing pain relief.

Clinical research has shown that, providing you use a good TENS machine, and understand when NOT to use it, significant short-term pain relief can be achieved.

TENS machines are currently medically recommended (depending on your country) for a wide range of painful problems including…

  • Arthritis
  • Back Pain
  • Bruising
  • Calf Strain
  • Dead Leg
  • Fibrositis Joint Pain
  • Headaches Migraines
  • Knee Pain
  • Lumbago Muscle Stress
  • Neck Pain
  • Neuralgia
  • Osteoarthritis
  • Period Pains
  • Postherpetic Neuralgia
  • Pregnancy/ Labour Pains
  • Rheumatism
  • Sciatica
  • Shoulder Pain
  • Sleeplessness
  • Spondylosis
  • Sports Injuries
  • Tennis Elbow
  • Tenosynovitis
  • Wrist Pain
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Image of four TNS machine pads on someone's back

What Does A TENS Machine Do?

A TENS machine (transcutaneous electrical nerve stimulation) works by you attaching patches (also known as ‘electrodes’) to your body carrying a mild electrical current.

These electrical impulses are designed to work in two ways –

1. To reduce the chance for your CNS (central nervous system) to transmit messages of pain to your brain, by flooding with lots of tiny messages.

2. To stimulate the production of endorphins – groups of hormones that include natural pain relievers.

The electrical current from the TENS machine is designed to stop the nerves sending pain sensation messages through your body to your brain. If the pain messages don’t reach your brain, then they can’t be processed correctly and sent back.

This ‘blocking’ of pain signals is ultimately what helps to relieve pain in the affected area. The whole concept actually relies on what is known the ‘Gate Control Theory’.

We have covered Gate Control Theory and how a TENS machine works in much more ‘How Does A TENS Unit Work?

Many doctors now actively recommend use of a TENS machine as the best form of treatment if rest is unsuccessful, although others may question the lack of clinical evidence behind them.

In certain cases, your doctor’s surgery may already offer training in correct use of the TENS machine, but now these are an established treatment the understanding of how they can help you is much better.

A Dial Scoring Pain Relief From A TENS Machine

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What Are The Benefits of TENS Machines?

Pain Relief

TENS machines are not designed to ‘cure’ the source of your pain, but rather to provide short-term pain relief – sometimes only for as long as they are being used, other times for hours afterwards.

Few Side Effects

They are very safe in as much as there is little that can go wrong (as long as read the instructions). They don’t carry side effects in the way that most modern drugs so and unlike some forms of vigorous exercise, there is little chance of the treatment actually making your pain worse.

Similarly, when they do provide powerful examples of pain relief, it gives you the opportunity to reduce other pain medications that may carry much more dangerous long-term effects.

Easy To Use

They are also non-invasive, while most are fairly small and quite portable. Certain models can even clip to a belt to provide you with pain relief throughout the day and beyond.


Because it is not a chemical designed to affect your mind or chemical balance within your body, TENS machines are considered non-addictive.

Small And Portable

Most TENS machines today are actually small enough to carry around with you. This means you could use them at work, at home – even on the train on your commute to work if you so desired.

Link to the page 'What Does A TENS Machine Do And What Makes A Good One'

Side Effects Of A TENS Machines.

Although I’ve just stated that TENS machines are relatively safe, there are always the odd danger, especially if you don’t read the manual.

The side effects that can happen include an allergic reaction to the electrodes (pads) or an uncomfortableness with the ‘tingling’ feeling of the electrical impulses.

Hypoallergenic patches can be purchased however that should cut out any allergic reaction if you need to.

One other warning though – placing the electrodes on your eyes is not a good idea unless you want an eye injury and similarly putting them on your neck can cause low blood pressure or muscle spasms.

However, as long as you read the guidance and take note of the people who should avoid using a TENS machine you should be fine.

Who Should NOT Use A TENS Machine?

  1. People with a pacemaker or other electrical implant.
  2. People with heart problems
  3. Pregnant women (at least don’t use near the pelvic area and consult you doctor first)
  4. People With Epilepsy. Electrical impulses have been known induce seizures.
  5. If you intend to use a TENS machine on a flight, make sure you get permission from the airline first.

What Does A TENS Machine Do – Using One At Home

As with any form of pain relief, the fact that it works for one person, does mean it will definitely work for someone else.

This is especially true with TENS machines because they can rely on a good understanding of how/ where to apply the TENS machine for various types of pain. We cover exactly what to look for in a good TENS machine further down in this article.

The quality of the TENS machine itself also varies greatly. This is then reflected in their price – typically varying in price for £40 up to £200 depending on various features.

As mentioned some doctor’s surgeries consider them to be essential medical equipment and so have one readily accessible for patients – however depending on the surgery/ your health service or your insurance, each treatment can work out quite costly.

Purchasing a mobile TENS machine of your own has many advantages –

  1. You can use it much more regularly
  2. You can use it when it is most convenient for you.
  3. You can vary the frequency.

This will help with making sure you do not build up a tolerance straight away. As DeSantana et al noted in concluding a clinical trial in 2007 this tolerance can be broken by regularly varying the frequency of the electrical pulses.

Alternatively, and even more effectively – keep the pulses at high intensity (the most efficient level according to the review by Vance et al for ‘Pain Management’ and instead vary the application sites of the electrodes. 

4) You can use it for a variety of pains or keep it just in case you develop new pains later in life. There are a range of studies showing it effectiveness in treating everything from osteoarthritic knee pain (Adedoyin et al) to Fibromyalgia (Lauretti et al)

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Conclusion –

So…what does a TENS machine do? Well, with the use of clever electrical pulses it can block the pain signals travelling to your brain.

This can provide essential pain relief for many people.

Of course, there is no guarantee that a TENS machine will work for everyone, but then no pain treatment does.

Perhaps the biggest vote for their effectiveness, and there is data that backs up their use as well, is that many family doctors now see them as a viable alternative to painkillers, without all the side effects.

If you do decide that a TENS machine could help you, just make sure you read the guidance on ‘What Makes A Good TENS Machine‘ or indeed our review of the best TENS machines available today (from a medical perspective) ‘What Is The Best TENS Machine To Buy?‘ before making your decision.

Getting the right device and using it properly really does make all the difference to it’s overall effectiveness.

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References –

1. DeSantana JM, Santana-Filho VJ, Sluka KA. (2007) Modulation between high- and low-frequency transcutaneous electric nerve stimulation delays the development of analgesic tolerance in arthritic rats. Archives Of Physical Medicine And Rehabilitation.

2. Carol GT Vance, Dana L Dailey , Barbara A Rakel & Kathleen A Sluka. (2014). Using TENS for pain control: the state of the evidence. Pain Management

3. Adedoyin RA, Olaogun MO, Fagbeja OO. (2002) Effect of interferential current stimulation in management of osteo-arthritic knee pain. Physiotherapy 88, 493–499 (2002).

4. Lauretti GR, Chubaci EF, Mattos AL. (2013). Efficacy of the use of two simultaneously TENS devices for fibromyalgia pain. Rheumatol. Int. 33, 2117–2122 (2013)