TENS Units for Pain: How They Work and Safe Use

How TENS works

A TENS unit has a control box with dials or buttons, wires and sticky electrode pads. The pads are placed on the skin around or near the painful area. The unit sends small electrical pulses, which feel like tingling, buzzing or tapping. Two main ideas explain why this might ease pain:

• Gate control. The pulses stimulate large touch nerves, which may "close the gate" on pain signals travelling to the brain.
• Endorphin release. At lower frequencies and stronger intensity, TENS may encourage the body's own pain-relieving chemicals.

TENS does not treat the cause of pain. It is used for short-term relief, often while doing exercises, gentle activities or sleeping preparations. Research reviews have found that TENS may help some people with certain pain conditions, such as knee osteoarthritis or some nerve pains, but overall evidence is limited and of mixed quality. Some guidelines do not recommend it for chronic low back pain. A trial of a few weeks, with a pain diary, helps decide whether it is worthwhile for your parent; see keeping a pain diary and talking to the doctor.

Who may consider TENS

A doctor or physiotherapist may suggest a trial in situations such as:

• Osteoarthritis pain in the knee, hand or neck;
• Muscle and joint pain that limits movement;
• Some nerve pains, after assessment;
• Pain after some surgeries, with surgeon's approval;
• Chronic pain where other measures give limited relief;
• as one tool within a plan of exercise, heat, pacing and medicine; see chronic pain in older adults.

It should not delay diagnosis. New, severe, unexplained or worsening pain needs a doctor.

Who should not use TENS, or must ask a doctor first

TENS is not safe for everyone. Do not use, or seek medical advice first, if:

• You have a pacemaker, implanted defibrillator, or other implanted electrical device. Electrical signals may interfere. This is the most important rule. Do not use TENS anywhere on the body unless the cardiologist or device clinic confirms it is safe.
• You have a heart rhythm problem or serious heart disease.
• You have epilepsy, particularly for electrodes near the head and neck.
• You are pregnant (not usually relevant in later life).
• You have a known or suspected cancer at the site, or unexplained lumps.
• You have a deep vein thrombosis, or a suspected clot, or electrodes would sit over a clot or swollen, red, hot leg; see swollen legs in older adults.
• The skin is broken, infected, rashy, burned, sunburnt or fragile.
• The area has reduced or absent feeling, such as in diabetic neuropathy, after stroke or with nerve damage. A person may not feel a burn or too-strong current. Use only with medical advice; see neuropathy foot care.
• You have dementia or confusion and cannot understand or report discomfort. A carer must supervise.
• You are unable to adjust the device or remove pads.
• The pain is undiagnosed, severe or sudden.
• You have an allergy to the adhesive of pads or gel.

Where electrodes must not go

Never place pads:

• on the front or sides of the neck, over the carotid artery, which can affect heart rate and blood pressure; see cervical collars and neck pain;
• across the chest or over the heart, or on the upper back near the heart if you have heart disease, without a doctor's advice;
• on the head or face, including near the eyes and mouth;
• over broken, inflamed or infected skin, wounds or rashes;
• over areas of numb skin;
• over implanted devices;
• over genitals;
• on the abdomen in pregnancy or with a hernia or bowel problems, unless advised;
• over swollen or clot-affected legs;
• over recent scars or surgical sites, unless the surgeon agrees.

Choosing a unit

1. Check with a doctor or physiotherapist before buying, particularly if you have heart, skin or nerve problems. 2. Safety certification. Choose a device sold with clear documentation, an intended use statement, safety standards and a warranty. Be wary of unbranded, unverified units; see spotting fake or poor quality care products and medical device licences and safe buying. 3. Easy controls. Large, clear buttons or dials, a screen that is readable, and a lock to stop accidental changes. People with arthritis or tremor need simple controls. 4. Intensity control with fine steps from zero, and a smooth ramp-up. A unit that jumps in power can cause a painful shock. 5. Modes. Most have several preset programmes (for example continuous, burst, modulated). Presets are usually enough for beginners. 6. Timer that switches off after a set period, such as 20 or 30 minutes. 7. Channels. Dual-channel units allow two pairs of electrodes. 8. Pads. Re-usable, self-adhesive pads in suitable sizes. Check you can buy replacements easily. 9. Power. Battery type, battery life and charging. Batteries should be easy to replace. 10. Lead wires that are strong and not easily pulled out. 11. Clip to attach to a belt or pocket. 12. Return and warranty; see equipment returns, warranty and servicing.

How to use a TENS unit safely

Follow the maker's instructions and any advice from a physiotherapist.

1. Turn the unit off and set the intensity to zero before attaching or removing pads or changing settings. 2. Prepare the skin. Clean with soap and water and dry; do not use creams or oils under the pad. Hair may need trimming but not shaving, since small cuts make the skin sore. 3. Place pads on intact, normal-feeling skin, around the painful area, about 2.5 cm or more apart, not touching each other. Common positions: either side of the painful spot, or above and below it. Do not place pads over the places listed above. 4. Connect leads firmly to the pads, and the unit. 5. Set the mode and timer. 6. Turn on and slowly increase intensity until you feel a strong but comfortable tingling, without muscle twitching that hurts or pain. It should never feel painful or burning. Reduce if it becomes uncomfortable. After a few minutes, the sensation may fade (accommodation); you can raise the intensity a little. 7. Use for the time advised, typically 20 to 40 minutes per session, a few times a day, or as the therapist says. Do not use continuously for hours. 8. Sit or lie comfortably. Do not use TENS while driving, operating machinery, cooking, bathing, showering or in water, or while sleeping, unless the maker specifically allows it. 9. At the end, turn the intensity to zero, switch off, and remove pads by peeling gently. 10. Check the skin under the pads for redness, irritation or burns. Mild pinkness that fades within an hour is common; persistent redness, blistering or itching means stop. 11. Store pads on their backing sheet in a sealed bag, and replace when sticky power is lost. 12. Keep a diary of pain levels, times used and settings, to see if it helps.

Common problems and tips

• Pads peeling off. Skin may be oily or hairy; clean the skin or trim hair; replace pads.
• Skin irritation. Try a different pad brand or position, ask the pharmacist about hypoallergenic pads, rest a day, and do not use on irritated skin.
• Muscle twitching painful. Lower the intensity or change the pad placement.
• No sensation. Check the battery, lead connections and pad contact. If the skin has lost feeling, stop.
• No pain relief. Try a different position, mode or time of day, or accept it may not work for you. Review after a few weeks.
• Dizziness, nausea or palpitations. Stop and seek medical advice.
• Electrical interference from phones, microwaves or other devices is not usual; keep the unit away from water and from other electrical devices; do not use near others who have implanted devices.

Combining TENS with other care

TENS works best within a plan.

• Exercise and movement, as taught by a physiotherapist; see exercise with arthritis and gentle exercises for knee and hip pain.
• Heat or cold, but not at the same time as TENS on the same area, and not on numb skin; see heat or cold for joint pain.
• Supports, such as knee sleeves or back belts, with caution so that pads and electrodes are not covered inappropriately; see knee support buying guide and back belts and lumbar supports.
• Medicines, prescribed by a doctor; see painkillers and older adults.
• Sleep and mood support; see sleep problems in older adults.
• Specific uses: using a TENS unit for back and knee pain.

When to ask a professional

Ask a doctor or physiotherapist before trying TENS, especially with a pacemaker, heart problems, diabetes, neuropathy, skin problems, epilepsy, cancer or unexplained pain. They can show you where to place pads and which settings to use. See a doctor if the pain is getting worse, if TENS gives no relief after a fair trial, or if you notice skin damage, dizziness or palpitations. Seek emergency help for chest pain, severe breathlessness or fainting.