Red light therapy has one of the best safety profiles of any therapeutic technology available to consumers. In over 4,000 published studies, serious adverse events are extremely rare. That said, side effects can occur, and certain populations should exercise caution or consult a physician before using RLT devices.

Common Minor Side Effects

These are generally mild, temporary, and dose-related:

  • Skin redness (erythema) — Usually resolves within hours; most common in fair-skinned individuals or when sessions are too long or too close
  • Warmth or tingling sensation — Normal, especially from near-infrared wavelengths. Should be comfortable — not hot
  • Mild headache — Occasionally reported after first sessions; usually resolves as the body adapts
  • Eye strain — From looking at the bright LEDs without protection. Prevented entirely by wearing goggles
  • Temporary fatigue — Some users experience tiredness after early sessions as the body responds to increased cellular activity

Overexposure Effects (Biphasic Dose Response)

RLT follows a "biphasic dose response" — the right dose is therapeutic, but too much can be counterproductive or mildly harmful. Overdosing by staying too long, too close, or using excessively powered devices can cause:

  • Temporary inflammation rather than anti-inflammation
  • Increased skin sensitivity or redness
  • Temporary reduction in the beneficial effects (the cells become temporarily unresponsive)

This is why standard protocols recommend 10–20 minute sessions — not 60+ minutes. More is not better above a therapeutic threshold.

Important: RLT Is Not UV Light

A common misconception is that RLT is similar to tanning beds and therefore carries cancer risk. It does not. UV wavelengths (200–400 nm) damage DNA and cause skin cancer. Red and near-infrared wavelengths (600–1100 nm) are on the completely opposite end of the spectrum and have no carcinogenic mechanism. They're fundamentally different technologies.

Genuine Contraindications — Who Should Consult a Doctor First

  • Active cancer or history of photosensitive cancer — RLT theoretically could stimulate cellular growth; always consult your oncologist
  • Photosensitizing medications — Some antibiotics (tetracyclines), NSAIDs, retinoids, and psychiatric medications increase light sensitivity
  • Lupus (SLE) and photosensitive autoimmune conditions — These individuals are often sensitive to visible light and may react to RLT
  • Epilepsy — Bright flashing or pulsing light can trigger seizures in photosensitive individuals; avoid pulsing RLT devices
  • Pregnancy — Insufficient data; consult your OB/GYN, though no harm has been demonstrated
  • Direct application over thyroid cancer or thyroid nodules — Given RLT's known thyroid effects, caution is warranted over thyroid tissue in these cases

What Red Light Therapy Does NOT Cause

  • Skin cancer (no UV radiation involved)
  • Sunburn
  • DNA damage
  • Addiction or dependency
  • Interaction with oral medications (it's topical light, not a drug)