Red light therapy is generally considered low-risk, but several groups of people should either avoid it entirely or use it only under medical guidance. The main concerns involve active cancer, photosensitizing medications, pregnancy, certain eye conditions, and skin disorders that react to heat. Here’s a closer look at each group and why the risk exists.
People With Active Cancer
Applying red light therapy directly over a tumor site is considered a contraindication. The concern is rooted in cell culture studies showing that light in the red and near-infrared range can stimulate the growth of cancer cells and increase their aggressiveness. Animal research reinforces this worry: one study on mice with subcutaneous melanoma found that high-dose red light (660 nm) significantly increased tumor size, while a separate study on thyroid cancer in mice showed faster tumor growth in the treated groups.
The picture is complicated. Some research suggests light therapy can damage tumors, enhance other cancer treatments, or stimulate the immune system. But because the evidence cuts both ways and the stakes are so high, the standard clinical position is to avoid red light therapy over or near any known malignancy. If you’re in active cancer treatment and considering red light therapy for side effects like mouth sores from chemotherapy, that’s a conversation to have with your oncologist, since the light would need to be directed away from the tumor site.
People Taking Photosensitizing Medications
Dozens of common medications increase how your skin and eyes react to light. If you take any of these drugs, red light therapy could cause unexpected skin reactions, burns, or eye irritation. The list of photosensitizing medications is long and spans many drug categories:
- Heart and blood pressure drugs: amiodarone, hydrochlorothiazide (and combinations containing it), amlodipine, atenolol
- Antibiotics: amoxicillin, certain tetracyclines
- Mental health medications: amitriptyline, aripiprazole, alprazolam, bupropion
- Pain medications: acetaminophen (in liquid form), butalbital combinations
- Immunosuppressants: azathioprine
- Skin treatments: acitretin, bexarotene
This is only a partial list. A published review catalogued well over a hundred oral medications with documented light sensitivity. If you’re unsure whether your medication qualifies, check the packaging for phrases like “protect from light” or “may cause photosensitivity,” and ask your pharmacist before starting any light-based therapy.
Pregnant Women
Red light therapy is generally not recommended during pregnancy. The North American Association for Laser Therapy has specifically recommended against using low-level light therapy directly over a developing fetus. A systematic review of laser therapy during pregnancy found that it is often listed as an absolute contraindication and used as an exclusion criterion in musculoskeletal research studies.
The issue isn’t that harm has been proven. It’s that almost no research has evaluated the safety of red light therapy on pregnant patients, and without that evidence, healthcare professionals default to caution. If you’re pregnant and dealing with musculoskeletal pain or skin concerns, treatment is typically postponed until after delivery.
People With Eye Conditions or No Eye Protection
Red light therapy poses real risks to the eyes when used improperly. The National Eye Institute highlighted a study showing that red light devices marketed for myopia treatment can exceed safety limits for the retina during the sustained exposure times these treatments require. Even devices using Class I lasers, which are safe for brief accidental viewing, may cause photochemical and thermal damage to the retina with longer use.
People with existing eye diseases, including retinal conditions and macular degeneration, face higher risk and should talk to an eye specialist before using any red light device. For everyone else, the rule is simple: always wear the protective eyewear that comes with your device. Many at-home panels and masks sit close to the face, and squinting or closing your eyes is not sufficient protection.
People With Melasma or Heat-Sensitive Pigmentation
If you have melasma, red light therapy deserves extra caution. Pure red light in the 630 to 660 nm range is relatively low-risk for pigmentation on its own. The problem is that many consumer devices, especially LED masks and full-body panels, also emit near-infrared wavelengths that penetrate deeper into the skin and generate significant heat. That heat directly stimulates the pigment-producing cells in your skin, a process called heat-induced melanogenesis.
Dermatologists report that the heat, not the red light itself, is the main culprit. Patients with melasma commonly notice darkening after two to six weeks of regular LED mask use, particularly with devices that include near-infrared wavelengths. High-intensity panels cause faster pigment flares. The good news is that improvement often occurs after stopping use. If you have melasma and want to try red light therapy, look for devices that emit only in the 630 to 660 nm range without near-infrared, use the lowest effective intensity, and keep sessions short to minimize heat buildup.
People With Photosensitive Epilepsy
Some red light therapy devices use pulsed or flickering light settings, which can be dangerous for the roughly 3% of epilepsy patients who have photosensitive seizures. Flashing lights between 5 and 30 flashes per second are the most likely to trigger seizures, and the consensus recommendation is that photosensitive individuals should not be exposed to flashes greater than three per second.
Color matters too. Deep, saturated red is specifically identified by the Epilepsy Foundation as one of the most problematic colors for triggering photosensitive responses. This makes pulsed red light therapy a uniquely bad combination for anyone with this condition. If you have photosensitive epilepsy, avoid any pulsed or flickering red light device entirely. Continuous-wave (non-pulsing) devices carry less seizure risk, but discussing it with your neurologist first is the safest approach.
People With a History of Skin Cancer
Even if you’re currently cancer-free, a personal history of skin cancer warrants caution. Because red light can stimulate cell proliferation, there’s a theoretical concern about encouraging the growth of precancerous or early-stage malignant cells that haven’t been detected yet. This doesn’t mean red light therapy is definitively harmful for skin cancer survivors, but medical guidance consistently recommends checking with a dermatologist before starting treatment, especially if you’ve had melanoma or have numerous atypical moles.
Risks With At-Home Devices
Consumer red light therapy devices are a growing market, and quality varies widely. The FDA has issued recalls for devices with faulty cord connectors that cause power interruptions and shutdowns. While that specific issue is more of an inconvenience than a danger, the broader concern is that at-home devices lack the oversight of clinical settings. Common user errors include holding panels too close to the skin (causing burns), using devices for far longer than recommended, and skipping eye protection.
If you fall into any of the groups above, the risks are amplified with at-home devices because there’s no practitioner monitoring your session. Even if you don’t have any contraindications, stick to the manufacturer’s recommended distances, session times, and protective gear.