What is a TENS machine? Could this help my period pain or endometriosis?

If you’ve been on social media recently, you may have noticed sponsored posts and ads for various small portable electrical devices. They claim to manage menstrual or endometriosis pain safely and without medication.

Most devices have a small box that generates an electrical impulse and wires connected to sticky pads that go on the abdomen.

So how are these devices supposed to stop your pain? Are they safe? Do they actually work?

Read more: Health Check: Are Painful Periods Normal?

These are mini-TENS machines

These devices use “transcutaneous electrical nerve stimulation,” better known as TENS. In other words, they apply small electrical pulses through the skin to stimulate certain types of nerves.

TENS machines are not new. They have been around since the 1970s and have been used for a variety of painful conditions, from muscle injuries to pain relief during childbirth.

However, compared to older models, these latest devices are compact and easy to carry discreetly. They are relatively easy to use, portable, you can use them at home and they cost around 50–200 Australian dollars.

It’s easy to see why such devices can be popular. Half of people with period pain say that over-the-counter medications such as ibuprofen do not relieve period pain. Most people with endometriosis report serious problems with adequate pain relief.

Read more: From sharp butt pains to period poo: 5 lesser-known menstrual cycle symptoms

How can TENS work?

All TENS devices generate small electrical pulses that are somewhat similar to mild electric shocks. These impulses are transmitted across the surface of the skin via adhesive pads.

You usually place these pads where you feel the pain. So for menstrual pain, which is usually at or below the navel but above the pubic area,. You can also place pads on your lower back or even on your coccyx (sacrum). This is because some nerves near the tailbone also affect the pelvic area.

The sticky sole of the TENS machine on the skin — You place two adhesive pads on your stomach or lower back.
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Here’s what we know so far:

The exact mechanisms by which TENS reduces pain are still unclear. There are likely to be many different paths.

First, we need to talk about the different types of nerves. Nociceptors are nerves that send “danger” impulses about existing or potential tissue damage. Sensory nerves in your skin transmit information about things like touch and pressure.

The gate control theory of pain states that the spinal cord has “gates” that can be opened or closed. When these gates are open, nerves can transmit these danger impulses through the spinal cord to the brain, where they can be interpreted as “pain.” If these gates are closed, these impulses cannot reach the brain as easily.

TENS machines, especially at high frequencies (over 50 pulses per second), tend to stimulate sensory nerves (located in your skin). These sensory nerves also send signals to your brain, but at a faster-than-dangerous rate.

These sensory signals can close “gates” in certain parts of the spinal cord. So if the TENS machine can stimulate enough of these sensory nerves in your skin, it will block at least some of these dangerous impulses from reaching the brain. The fewer danger impulses reach the brain, the less likely you are to feel pain.

Closed farm gate across dirt track — TENS machines can close the “gates” in certain parts of the spinal cord, so fewer “danger” impulses reach the brain.
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Then there is the concept of endogenous opioids as pain relievers. These are pain-relieving chemicals that the body produces on its own.

TENS machines stimulate the release of these chemicals, and depending on the frequency of stimulation, different types of endogenous opioids are released.

Read more: Explained: What is pain and what happens when we feel it?

So does TENS work?

For menstrual pain

in 2022 A systematic review found four studies investigating TENS for the treatment of primary dysmenorrhea (periodic pain that occurs without any physical changes in the pelvis).

Menstrual pain was significantly reduced when high-frequency TENS (more than 50 pulses per second) was compared to sham TENS (where the machine looks the same but does not deliver a pulse).

This is consistent with an older Cochrane review that found similar benefits.

The pain-relieving effect usually lasts only when the device is working.

Because of endometriosis

Endometriosis is when tissue similar to the lining of the uterus is found outside the uterus, usually in the pelvic area. There is only one study of TENS for pelvic pain caused by endometriosis.

This study compared two types of TENS, one using a higher frequency for 20 minutes twice a day and one using a lower frequency for 30 minutes once a week. Both types of pads were placed on the tailbone and the women were told to pulse “strong but comfortable.”

Both species improved pelvic pain, pain after sex, and quality of life, but not menstrual pain. This was a very small study (11 women in each group) and there was no control or placebo group. So we need larger studies with a proper control group to be sure if TENS works for endometriosis pain.

Read more: I have painful periods; could it be endometriosis?

Is it safe?

Most studies have shown no side effects when the pads are used on the abdomen or lower spine.

However, if you turn up the intensity too high, it can be uncomfortable. You can also get a rash from the glue on the cushions.

Read more: The first period can be a shock. 5 ways to support your child when they get theirs

Which one should I buy?

All TENS machines should allow modification in intensity (how strong the pulse feels). Some also allow replacement frequencies (how often the pulse occurs).

If you intend to use the device occasionally (less than 4-5 days per month), you may need a device that allows you to change the intensity.

For best relief, the machine should be raised high enough to give noticeable pulses but not be painful. So you have to find your comfort level.

For menstrual pain, a high frequency (more than 50 pulses per second) shows better results than a low frequency (usually 2–5 pulses per second). So make sure the device you are going to buy is set to high frequency or you can change the frequency.

A woman is lying on a sofa holding her stomach and head — Many people find it difficult to manage period pain. So would TENS help?
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For people with endometriosis, it’s a little more complicated. You’ll probably want to use the device more than a few days a month.

Unfortunately, as with regular opioid pain relievers, regular use of TENS can lead to people becoming tolerant of its pain-relieving effects, meaning it doesn’t work as well as it did when they first started using it.

One possible solution to tolerance is to use mixed-frequency TENS where high and low frequencies are alternated. You can also slowly increase the intensity level over time.

TENS also doesn’t work well when people are taking opioids regularly. This is important because people with endometriosis often take opioid medications for pain relief. If you take opioids regularly, high-frequency TENS is likely to be a better option.