A magnet can pause a defibrillator, so check these device warnings first

Key takeaways

• The American Heart Association says people with pacemakers or implanted defibrillators should keep magnets at least 6 inches away and avoid magnetic mattress pads, ab stimulators and electronic body-fat scales.
• If you have nerve damage in your feet, the NIH warns you can burn them without feeling it, so skip heating pads and test water with a thermometer.
• Common medicines, from doxycycline to ibuprofen, plus the herb St. John’s wort, can make skin react badly to sunlight and UV light.
• Flashing light at 3 to 60 flashes per second can trigger seizures in people with photosensitive epilepsy, so check the flash rate on any device that flickers.
• Under its January 2026 policy, the FDA does not plan to check whether low-risk wellness products follow labeling rules, so you are the one who has to read the warnings page.

In May 2021, the Food and Drug Administration posted an unusual notice about phones and smartwatches¹. Some contain magnets strong enough to switch a pacemaker or implanted defibrillator into “magnet mode,” which pauses its normal work. The FDA tested some of these products and confirmed it¹.

Doctors use magnet mode on purpose during procedures. Outside the clinic, a defibrillator in magnet mode may miss a dangerously fast heartbeat, and a pacemaker may switch to pacing at a fixed rate¹.

The agency judged the danger to patients to be low, and at the time it had no reports of anyone being harmed¹. But the lesson reaches past phones. Magnetic bracelets, magnetic mattress pads, ab stimulators and body-fat scales all appear on the American Heart Association’s list of things to keep away from or avoid with an implanted heart device².

Most wellness devices are low risk for most people. Yet the same short list of exceptions shows up across very different products: implanted electronics, numb skin, pregnancy, certain medicines and herbs, light-triggered seizures and blood clots. This guide gathers them in one place.

Many wellness devices reach you with no one checking the warnings

Under guidance updated on January 6, 2026, the FDA treats a product as a low-risk general wellness product if it is meant only for general wellness and poses low risk to users³. For those products, the FDA’s device center does not plan to check compliance with rules on labeling, registration or reporting injuries³.

So the warnings page on a “wellness” massage gun or light panel was written by the maker, and nobody at the agency has to approve it.

The FDA does draw lines. It says a skin-rejuvenating laser is not low risk because it can burn skin and eyes, and neither is a brain stimulator claiming to improve memory³. Devices cleared for a medical use get more review, as our buyer’s map to wellness devices explains.

Implanted heart devices: magnets and current are the concern

If you have a pacemaker or an implantable cardioverter-defibrillator (ICD), a device that shocks the heart out of a deadly rhythm, two things matter most: strong magnets and electricity passed through your body.

The American Heart Association advises, on its page last reviewed in October 2024²:

• Magnets: Keep them at least 6 inches from the implant. In an ICD, a magnet can disable the lifesaving shock. Don’t wear magnetic bracelets or necklaces close to the implant.
• Magnetic bedding: Skip magnetic pillows and mattress pads, which some adjustable or smart beds include.
• Ab stimulators and electronic body-fat scales: The AHA says both are likely to interfere and should be avoided.
• TENS units: These small units send mild current through skin pads to ease pain. They may be acceptable with an ICD if you take precautions, but the pads shouldn’t go on your torso.
• Diathermy: One type of this deep-heat treatment, used in some physical therapy clinics, can permanently damage the device. Consult your heart team first.

Some surprises run the other way. The AHA lists massage chairs and pads, heating pads, handheld back massagers, hot tubs and tanning beds as posing little or no known risk to the implant itself, with motors kept at least 6 inches away².

But “little risk to the implant” is not “safe for your heart.” Heat still strains the heart, as our sauna article explains. And a PEMF (pulsed electromagnetic field) mat uses changing magnetic fields, so ask your device clinic before lying on one.

The AHA also advises carrying your device ID card and telling every health professional about your implant, including dentists and imaging technicians². It makes sense to tell massage and physical therapists, too.

Heat is a dose, and some bodies can’t feel it or shed it

Saunas, hot tubs, infrared mats, heating pads and foot spas ask your body to sense warmth and cool itself. Three groups have trouble with one or both.

People with nerve damage. Diabetes can dull feeling in the feet. The National Institute of Diabetes and Digestive and Kidney Diseases warns that people with this nerve damage can burn their feet without realizing it⁶. It advises against heating pads and hot water bottles on the feet, and suggests testing the water you wash your feet in with a thermometer: 90°F to 95°F is safe⁶. Apply the same logic to any heated mat or foot bath.

People taking certain medicines. In September 2025, the Centers for Disease Control and Prevention listed drug classes that can weaken heat tolerance⁷. Examples:

• Water pills (diuretics) such as furosemide can dehydrate you and upset your electrolytes.
• Beta blockers such as metoprolol reduce sweating and blood flow to the skin.
• Sedating antihistamines such as diphenhydramine reduce sweating.
• Antipsychotics, tricyclic antidepressants and the seizure drug topiramate can impair cooling.
• Lithium can become toxic when you’re dehydrated, and stimulants such as amphetamine raise body temperature.

The CDC notes the list isn’t complete⁷. A pharmacist can check yours.

People who are pregnant. The CDC says pregnancy can make heat illness more likely and can bring it on sooner. It adds that high body temperature and fever during pregnancy have, in some cases, been tied to birth defects and other problems⁸. Ask your prenatal provider before using a sauna or hot tub.

Light: what’s in your pill bottle, and how fast it flashes

Medicines and herbs. The FDA describes two kinds of drug-related light sensitivity⁹. A phototoxic reaction is skin irritation, often like a sunburn, that can appear within hours. A photoallergic reaction is an allergic rash that may take several days.

The FDA’s list of drugs that can cause them is long. It includes the antibiotics doxycycline and ciprofloxacin, antihistamines such as cetirizine, statins, water pills, ibuprofen and naproxen, birth control pills and the acne drug isotretinoin⁹. Not everyone who takes them reacts⁹.

Herbs belong on the list too. The NIH’s National Center for Complementary and Integrative Health says St. John’s wort, taken in large doses or put on the skin, might cause severe skin reactions in sunlight¹⁰. It also weakens many drugs, including birth control pills and warfarin¹⁰.

What about a red-light panel? The FDA’s warnings concern sunlight and ultraviolet light, including tanning beds⁹. We found no research testing these reactions under red or near-infrared panels, so treat it as an open question. Ask your pharmacist first, and start with a short session.

Flashing light and seizures. The Epilepsy Society, a British charity, says about 3% of people with epilepsy are photosensitive¹¹. Flashing at 3 to 60 times per second can trigger a seizure, and 16 to 25 flashes per second is the most likely range¹¹.

If a meditation goggle or brain-training gadget flickers, find out its flash rate. Anything between 3 and 60 per second sits inside that trigger range, so anyone with epilepsy should ask a neurologist first.

Caught off guard by flashing? The charity advises putting a hand fully over one eye and looking away¹¹.

Massage guns and vibration: protect clots and fragile tissue

Hands-on massage is low risk for most people, according to NCCIH¹². But the center notes rare serious harms: a blood clot, nerve injury or a broken bone. Some of the reported cases involved vigorous massage, like deep tissue work, or people at higher risk, such as older adults¹².

A massage gun or vibration plate delivers strong, repeated force. So never pound or vibrate a leg that is newly swollen, tender and painful. Those are signs of deep vein thrombosis (DVT), a clot in a deep vein, says the National Heart, Lung, and Blood Institute¹³.

A clot that travels to the lungs, called a pulmonary embolism, causes shortness of breath and pain when you breathe. Call your provider right away about DVT symptoms¹³.

If you take a blood thinner, bruise easily, have thin bones or are in cancer treatment, ask before using strong percussion. People with cancer may need lighter pressure in sensitive areas¹².

A master table: who should check before using what

“Ask first” means talk with the clinician who knows your condition before your first session. Your manual may add more. Our device-by-device articles cover whether each one works.

Device	Ask first or skip if you…	Why	Source
Magnetic bracelets, pillows, mattress pads	Have a pacemaker or ICD	Magnets can trigger magnet mode; in an ICD, they can disable shocks	12
PEMF mats	Have a pacemaker, ICD or other implant	They use magnetic fields; AHA advises avoiding magnetic pads	2
TENS units	Have an ICD or pacemaker, are pregnant, or want pads on the head, neck or chest	AHA says not on the torso; one cleared TENS label rules out pregnancy and advises against use with demand pacemakers	25
Ab stimulator belts, body-fat scales	Have an implanted heart device	Likely to interfere; AHA says avoid	2
Heating pads, heated mats, foot spas	Have numb feet or nerve damage	You can burn without feeling it	6
Saunas, hot tubs, infrared cabins	Are pregnant, or take diuretics, beta blockers, sedating antihistamines, lithium or stimulants	Heat illness comes sooner in pregnancy; some drugs weaken cooling	78
Red-light and LED devices	Take light-sensitizing drugs or St. John’s wort	Skin reactions are documented with sunlight and UV; red light untested	910
Flashing light goggles or gadgets	Have epilepsy or a family member with it	3 to 60 flashes per second can trigger seizures	11
Massage guns, vibration plates	Have a swollen, painful leg, take blood thinners, or have fragile bones	Rare clots and fractures are reported with vigorous massage	1213
Cold plunges	Have heart rhythm problems or Raynaud’s	Covered in our cold plunge article	—

How solid is each warning?

Warning	Evidence level	What it rests on
Strong magnets switch implanted heart devices into magnet mode	Strong evidence	A built-in feature, confirmed by FDA tests with consumer magnets1
Phone and watch magnets have injured people with implants	Not enough evidence	FDA knew of no injuries in 20211
Heating pads are safe on numb feet	Evidence says no, or unsafe	NIH warns of burns people don’t feel6
Getting overheated is harmless in pregnancy	Evidence says no, or unsafe	CDC links high temperature and fever to birth defects in some cases8
Some drugs and St. John’s wort cause sun reactions	Strong evidence	FDA and NCCIH910
Red-light panels trigger those reactions	Not enough evidence	Our search found no studies; FDA’s warnings cover sunlight and UV9
Flicker at 3 to 60 per second triggers seizures in photosensitive epilepsy	Strong evidence	Epilepsy Society11
Massage or vibration dislodges clots	Not enough evidence	Rare reports; size of risk unknown12

How to read the warnings page in a manual

The warnings page is worth five minutes, especially because a wellness product’s label may never have been reviewed by the FDA³.

A real example shows how specific these pages get. In 2005, the FDA cleared a prescription TENS unit called E-Stim II. Its labeling said not to use it across the head, over the carotid sinus in the neck, or during pregnancy. It also said the unit was not recommended for people with demand pacemakers, because the current can block their output⁵.

It also warned that pads across the neck or mouth could cause throat spasms severe enough to close the airway. And it noted that blocking pain can hide a warning sign of a worsening problem⁵.

When you read a manual, look for:

• Placement rules. Where must pads, heads or panels never go?
• Time and intensity limits. A maximum session length is a safety limit, not a suggestion.
• Named conditions. Search for implants, pregnancy, diabetes, epilepsy, clots and cancer.
• What’s missing. A manual with no warnings at all calls for more caution, not less.

Before your first session: a checklist and a script

Run through this list for each new device, and again if your health or medicines change.

1. Do I have anything implanted? A pacemaker, ICD, nerve stimulator or pump means a call to the clinic that manages it¹².
2. Does it use a magnet, a current or flashing light? Those features drive most implant and seizure cautions²¹¹.
3. Can I feel heat and pressure normally there? If not, use a thermometer, a timer and low settings⁶.
4. Am I pregnant? Ask before any heat device⁸.
5. What do I take? Check prescriptions, over-the-counter drugs and herbs against the heat and light lists⁷⁹¹⁰.
6. Is any area swollen, painful or newly injured? Keep percussion away and get it checked¹³.
7. Am I on the contraindications page? Then don’t use the device⁴.
8. Do I know the stop signs? Stop for chest pain, fainting, trouble breathing, a seizure or a blistering burn. Call 911 for the first four.

Not sure how to ask? Try this with your pharmacist:

“I’m thinking about using a [device] for about [minutes], [times] a week. I take [medicines and supplements], and I have [conditions or implants]. Does anything here make this risky?”

Many natural-health readers believe a remedy should fit the person. Devices are no different. Knowing your own exceptions is part of listening to your body, and it lets you enjoy warmth, light and touch with fewer surprises.

When something goes wrong: report it, and read other reports

The FDA’s MAUDE database collects reports of device problems from makers, hospitals and the public. It’s updated monthly and holds about 10 years of reports¹⁴. On the MAUDE search page, you can enter a brand name or product code.

Read results with care. The FDA says these reports can’t show how often problems happen, and a report alone doesn’t prove the device caused the harm¹⁴. Many problems are never reported¹⁴. Use MAUDE to learn what has gone wrong, not to rank brands.

If you’re hurt, report it to the FDA’s MedWatch program online, on consumer Form FDA 3500B, or at 1-888-INFO-FDA (1-888-463-6332)¹⁵. Your clinician isn’t required to report for you, so file it yourself if needed¹⁵.

If an ad promised something the device couldn’t do, tell the Federal Trade Commission at ReportFraud.ftc.gov.

Questions readers ask

The bottom line

Most wellness devices are low risk for most people, and many of their manuals are never checked by a regulator. A short list of exceptions does most of the harm: implanted heart devices near magnets or current, numb skin under heat, pregnancy and overheating, light-sensitizing medicines and herbs, flashing light with epilepsy, and pressure on a possible blood clot.

Before you plug anything in, read the contraindications, run the checklist and ask a pharmacist about your medicines. If something goes wrong, stop, get care, and report it to the FDA so the next person has better information.

Related reading

• “FDA registered” isn’t “FDA approved”: a buyer’s map to wellness devices
• Red-light therapy’s strongest evidence is for cancer mouth sores, not wrinkles
• The famous sauna longevity study used Finnish saunas, not infrared cabins
• A cold plunge eases soreness but can shrink your muscle gains
• What happens when you don’t tell your doctor about supplements

Sources

1. U.S. Food and Drug Administration. “Magnets in Cell Phones and Smart Watches May Affect Pacemakers and Other Implanted Medical Devices.” FDA, 2021. fda.gov
2. American Heart Association. “Devices That May Interfere With ICDs and Pacemakers.” AHA, 2024. heart.org
3. U.S. Food and Drug Administration. “General Wellness: Policy for Low Risk Devices.” FDA guidance, 2026. fda.gov
4. U.S. Food and Drug Administration. “Device Labeling Guidance #G91-1 (Blue Book Memo).” FDA, 1991. fda.gov
5. U.S. Food and Drug Administration. “510(k) K050435: E-Stim II Transcutaneous Electrical Nerve Stimulator.” FDA, 2005. accessdata.fda.gov
6. National Institute of Diabetes and Digestive and Kidney Diseases. “Diabetes & Foot Problems.” National Institutes of Health, 2017. niddk.nih.gov
7. Centers for Disease Control and Prevention. “Heat and Medications – Guidance for Clinicians.” CDC, 2025. cdc.gov
8. Centers for Disease Control and Prevention. “Heat and Pregnancy.” CDC, 2024. cdc.gov
9. U.S. Food and Drug Administration. “The Sun and Your Medicine.” FDA. fda.gov
10. National Center for Complementary and Integrative Health. “St. John’s Wort.” National Institutes of Health, 2025. nccih.nih.gov
11. Epilepsy Society. “Photosensitive Epilepsy.” Epilepsy Society, 2025. epilepsysociety.org.uk
12. National Center for Complementary and Integrative Health. “Massage Therapy: What You Need To Know.” National Institutes of Health, 2019. nccih.nih.gov
13. National Heart, Lung, and Blood Institute. “Venous Thromboembolism: Symptoms.” National Institutes of Health, 2022. nhlbi.nih.gov
14. U.S. Food and Drug Administration. “About Manufacturer and User Facility Device Experience (MAUDE).” FDA. fda.gov
15. U.S. Food and Drug Administration. “Reporting Serious Problems to FDA.” FDA MedWatch. fda.gov