MRI is not bad for you. It uses powerful magnets and radio waves to create images of your body, with no ionizing radiation involved. Unlike CT scans or X-rays, which deliver small doses of radiation that accumulate over a lifetime, MRI produces none. For the vast majority of people, the procedure is safe and carries no lasting health effects. That said, there are real risks in specific situations that are worth understanding before you go in.
No Radiation, but Not Zero Energy
The reason MRI is considered safer than many other imaging tools is straightforward: it doesn’t use the type of energy that damages DNA the way X-rays and CT scans do. Instead, the machine generates a strong magnetic field and pulses of radio-frequency energy. Your body absorbs some of that energy as heat, a process measured by something called the specific absorption rate (SAR). International safety standards cap whole-body heat absorption at 2 watts per kilogram for routine scans, and the FDA sets its own ceiling at 4 watts per kilogram over 15 minutes. Modern scanners are designed to stay within these limits automatically.
In practice, most people feel little or no warmth during a scan. The heating effect increases with stronger magnets and longer scan times, which is why technologists monitor these parameters closely. Burns are rare and typically linked to specific circumstances, like skin-to-skin contact, coiled wires, or metallic objects on the body, not to the scan itself operating normally.
What About Long-Term Effects?
Some laboratory studies have found that exposure to strong magnetic fields can temporarily increase certain types of DNA damage in isolated blood cells, with the effect growing as exposure time lengthens. In one study, human blood cells exposed to a 3-Tesla MRI for up to 89 minutes showed a measurable increase in single-strand DNA breaks compared to unexposed cells. However, these are findings in cells studied under controlled conditions, and comprehensive reviews have concluded that static magnetic fields alone have no or extremely small effects on cell growth and genetic toxicity in living people. No long-term health consequences, including cancer, have been established from diagnostic MRI use in patients.
The Noise Is Louder Than You’d Expect
One risk that catches people off guard is how loud the machine is. MRI scanners at 3 Tesla can produce sound levels exceeding 105 decibels, roughly comparable to a rock concert or a chainsaw. At 7 Tesla, used mostly in research settings, levels can reach nearly 122 decibels. The FDA caps the maximum allowable sound at 140 decibels and requires that time-averaged noise with hearing protection stay at or below 99 decibels.
This is why you’re given earplugs or headphones before every scan. Well-fitting earplugs reduce noise by 10 to 30 decibels, which brings exposure within safe limits for the duration of a typical exam. If you aren’t offered hearing protection, ask for it. Skipping it during a long scan could genuinely risk temporary or permanent hearing changes.
Contrast Dye Carries Its Own Risks
Not every MRI involves contrast, but when it does, you’ll receive an injection of a gadolinium-based agent that helps certain tissues show up more clearly. Most people tolerate it fine. In a study of over 10,600 contrast-enhanced MRI exams, 32 allergic-type reactions occurred. Of those, 75% were mild (hives, nausea, minor itching), 12.5% were moderate, and 12.5% were severe. Severe reactions are rare but real, making it important to tell your technologist about any previous reactions to contrast agents.
The bigger concern with gadolinium involves your kidneys. In people with severely reduced kidney function (a filtration rate below 30), the contrast agent can trigger a serious condition called nephrogenic systemic fibrosis, which causes hardening, tightening, and thickening of the skin and can affect internal organs. This condition has not been reported in people with normal kidney function. If you’re over 60, have diabetes, or have high blood pressure, your doctor will likely check your kidney function with a blood test before ordering a contrast MRI.
Gadolinium Stays in Your Body
The FDA has confirmed that trace amounts of gadolinium remain in the body, including the brain, for months to years after injection. This retention is greater with older, linear forms of the contrast agent compared to newer, macrocyclic types. So far, gadolinium retention has not been directly linked to adverse health effects in people with normal kidneys, and the FDA’s position is that the benefits of contrast-enhanced MRI still outweigh the potential risks. Still, the FDA now requires a patient medication guide be provided before every gadolinium injection and recommends that clinicians minimize repeated contrast studies when possible, especially in pregnant women, children, and people with inflammatory conditions.
Metal Implants and Pacemakers
The magnetic field inside an MRI scanner is extraordinarily strong, typically 1.5 to 3 Tesla, or roughly 30,000 to 60,000 times the strength of Earth’s magnetic field. This means any ferromagnetic metal in or on your body can move, heat up, or malfunction. Traditional pacemakers and implantable defibrillators are considered incompatible with MRI because the magnetic field can interfere with their programming, overheat their leads, or cause them to deliver inappropriate shocks.
Newer “MRI-conditional” pacemakers and defibrillators exist and can be safely scanned under specific conditions, typically at 1.5 Tesla with limited energy settings. These devices still need to be reprogrammed before and after the scan, and a cardiologist is usually present during the exam. If you have any implanted device, including joint replacements, spinal hardware, cochlear implants, or aneurysm clips, tell the MRI team. Many modern orthopedic implants are MRI-safe, but confirmation is always required before you enter the scanner room.
Pregnancy
MRI is generally considered safe during pregnancy. Studies have shown no significant harm at 1.5 or 3 Tesla in any trimester. As a precaution, many guidelines recommend using 1.5 Tesla during the first trimester when both options are available, since theoretical risks like tissue heating are slightly higher at stronger field strengths. The real concern during pregnancy is gadolinium contrast. A large population study found that contrast exposure during pregnancy was associated with a higher risk of stillbirth, neonatal death, and certain childhood skin conditions, particularly when exposure occurred in the first trimester. For this reason, gadolinium is avoided during pregnancy unless absolutely necessary.
Claustrophobia and Anxiety
About 2.3% of patients scheduled for an MRI cannot complete the scan or need sedation because of claustrophobia. That translates to roughly 2 million failed or terminated MRI procedures worldwide each year. Among patients who already experience anxiety, the rate of claustrophobic reactions jumps to around 35%.
If you know enclosed spaces are difficult for you, there are options. Newer wide-bore and short-bore scanners have reduced claustrophobia rates by a factor of three compared to conventional machines, bringing the rate below 1% in some studies. Open MRI scanners, which have a gap in the magnet instead of a full tunnel, allowed over 90% of previously claustrophobic patients to complete their scans in one study. The tradeoff is that open scanners typically operate at lower field strengths, which can mean slightly lower image quality for certain exams. Sedation is another option, though facilities will often try a different scanner type first to avoid the risks that come with sedation.
If you’re anxious but want to avoid medication, ask the facility what type of scanner they use, whether you can go in feet-first (for non-head scans), and whether they offer music or a mirror that lets you see out of the bore. These small adjustments make a real difference for many patients.