Red light therapy is widely regarded as one of the safest therapeutic modalities available today. Unlike UV light, prescription medications, or invasive procedures, photobiomodulation at red and near-infrared wavelengths carries a remarkably low risk profile. However, that doesn't mean side effects are impossible. Understanding what can happen — and why — helps you use red light therapy confidently and safely.
In this guide, we break down every known side effect, explain the underlying causes, identify who may be at higher risk, and share practical tips for avoiding problems entirely.
Are Side Effects Common?
The short answer is no. Across thousands of clinical studies and decades of research, serious adverse events from red light therapy are extremely rare. A 2019 review published in the Journal of Biophotonics analyzed over 1,000 photobiomodulation studies and found that the vast majority reported no adverse effects. When side effects did occur, they were overwhelmingly mild and temporary.
That said, red light therapy does involve delivering energy to biological tissue, and individual responses can vary. Here are the side effects that have been documented in clinical literature and user reports.
Temporary Redness or Warmth
The most commonly reported side effect is mild skin redness (erythema) or a warm sensation in the treated area. This typically appears during or immediately after a session and resolves within 30 minutes to a few hours. It's caused by increased blood flow to the area — which is actually part of the therapeutic mechanism — rather than any tissue damage.
If you experience persistent redness lasting more than a few hours, you may be using too high an irradiance, sitting too close to the device, or treating for too long. Reducing session time or increasing your distance from the panel usually resolves the issue.
Eye Strain and Sensitivity
Red light therapy devices emit bright visible and near-infrared light. While red and NIR wavelengths are not inherently damaging to the retina at therapeutic doses (unlike UV or blue light), prolonged direct staring at high-intensity LEDs may cause temporary eye discomfort, headaches, or light sensitivity.
Most manufacturers include protective goggles with their devices, and we strongly recommend using them — especially with high-powered panels. Near-infrared light (800–850nm) is particularly important to shield against because it's invisible to the naked eye, meaning your blink reflex won't activate to protect you.
Recommended Eye Protection
If your device didn't include goggles, or you need a replacement pair, look for glasses rated for 600–900nm wavelengths. You can find affordable options on Amazon:
Headaches
Some users report mild headaches during their first few sessions, particularly when treating the face or forehead area. This appears to be related to the increased nitric oxide release and vasodilation that red light therapy promotes. For most people, this side effect diminishes after a few sessions as the body adapts.
If headaches persist, try shorter sessions (5 minutes instead of 10–15), treat areas farther from the head, or increase the distance between you and the device. Always use eye protection, as squinting at bright light can also contribute to tension headaches.
Temporary Skin Tightness or Dryness
A small number of users notice mild skin tightness or dryness after sessions, particularly on the face. This is thought to result from the mild heating effect of the LEDs and possibly from increased cellular turnover. Applying a gentle moisturizer after treatment typically addresses this completely.
The "Healing Crisis" or Initial Flare-Up
Some users with inflammatory skin conditions like acne or rosacea report a brief worsening of symptoms during the first week or two of treatment. While not well-documented in clinical literature, this phenomenon is commonly described in user communities and may reflect increased cellular activity and detoxification processes before the anti-inflammatory effects fully take hold.
If you experience an initial flare-up, consider reducing your session frequency to every other day and gradually increasing as your skin adjusts.
Biphasic Dose Response: More Isn't Better
One of the most important concepts in red light therapy is the biphasic dose response (also called the Arndt-Schulz law). Research consistently shows that there's an optimal dosing window for photobiomodulation: too little light produces no benefit, the right amount stimulates healing, and too much can actually inhibit cellular function or cause mild tissue stress.
A 2012 study published in Dose-Response confirmed that excessive energy densities (typically above 50–60 J/cm²) could reduce or negate therapeutic effects. This doesn't mean high doses are dangerous per se, but it underscores why following manufacturer guidelines for session duration and distance matters.
Safe Dosing Guidelines
For most conditions, research supports energy densities between 3–30 J/cm² per session. A typical home panel session of 10–15 minutes at 6–12 inches away falls well within this range. Read our protocol guide for detailed dosing recommendations by condition.
Who Should Be Cautious?
While red light therapy is safe for the vast majority of people, certain groups should exercise extra caution or consult a healthcare provider before starting treatment:
People taking photosensitizing medications. Some antibiotics (tetracyclines, fluoroquinolones), retinoids (tretinoin, isotretinoin), certain chemotherapy drugs, and some herbal supplements (St. John's Wort) increase skin sensitivity to light. While red and NIR wavelengths are far less problematic than UV in this regard, it's wise to start with shorter sessions and monitor your skin's response.
People with active cancer. Because red light therapy stimulates cellular metabolism and proliferation, most experts recommend avoiding treatment over or near areas with known active tumors. While there is no definitive evidence that red light therapy promotes cancer growth in humans, the precautionary principle applies. Note that red light therapy has actually been used successfully in clinical settings to manage treatment side effects like oral mucositis from chemotherapy.
People with epilepsy or seizure disorders. Some red light therapy devices have a pulsing mode. While the default continuous-wave mode presents no seizure risk, rapidly pulsing visible light could theoretically trigger photosensitive seizures in susceptible individuals. If you have epilepsy, use continuous-wave mode only and avoid staring directly at the LEDs.
Pregnant women. There is no evidence that red light therapy harms a developing fetus, but there's also limited clinical data specifically studying its use during pregnancy. Many practitioners consider it likely safe, particularly for facial or extremity treatments, but recommend avoiding direct treatment of the abdomen as a precaution. Consult your OB-GYN before starting any new therapy during pregnancy.
For a deeper dive into who should avoid red light therapy entirely, see our complete safety guide.
How to Minimize Side Effects
Virtually all reported side effects from red light therapy are avoidable with a few simple practices. Start with shorter sessions (5–8 minutes) and gradually increase to your target duration over the first week. Always wear protective eyewear, especially with high-powered panels. Follow the manufacturer's recommended treatment distance — typically 6–18 inches for full-body panels. Stay hydrated, as increased cellular metabolism does require adequate water intake. And most importantly, resist the temptation to overdo it. Consistency at moderate doses beats aggressive treatment every time.
Recommended Safe & Effective Devices
Quality devices with proper safety certifications make a big difference. The Hooga HG PRO 300 is an excellent entry-level panel with solid irradiance and built-in eye safety features.
The Bottom Line
Red light therapy has one of the best safety profiles of any wellness modality available today. Serious side effects are essentially unheard of in the published literature, and the mild, temporary effects some users experience — slight redness, warmth, occasional headaches — are easily managed by adjusting session parameters. By following dosing guidelines, using eye protection, and starting conservatively, you can enjoy the benefits of red light therapy with minimal risk.
Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before starting any new therapy, especially if you have a pre-existing medical condition or are taking medications.