Red light therapy has not been shown to cause cancer in humans, and the evidence so far suggests it is safe for skin exposure

Red light therapy uses wavelengths of light between 600 and 1000 nanometers—the red and near-infrared range—to stimulate cells. Unlike ultraviolet (UV) light, which damages DNA and is a known cancer risk, red light does not carry enough energy to break chemical bonds in DNA. The concern sometimes arises because light therapy sounds similar to sun exposure, but the mechanism is fundamentally different.

No human studies have documented red light therapy causing cancer, even after decades of use in medical settings. The largest body of safety data comes from dermatology and wound healing research, where red light has been used since the 1990s. That said, the research on long-term effects remains limited, and some questions about safety in specific populations have not been fully answered.

Key Takeaways

  • Red light therapy operates at wavelengths that cannot damage DNA directly, which is the mechanism by which UV light causes skin cancer.
  • No human cases of cancer have been attributed to red light therapy in medical literature, despite widespread clinical use for over 25 years.
  • Safety data is strongest for short-term skin exposure; long-term effects from repeated home use have not been studied extensively.
  • People with a personal or family history of melanoma should discuss red light therapy with their doctor before use, as individual risk factors may matter.

How red light differs from UV light at the cellular level

The reason UV light causes cancer and red light does not comes down to energy. UV radiation carries enough energy per photon to break the chemical bonds that hold DNA together—a process called ionization. When UV light damages DNA, cells either die or sometimes survive with mutations. Over time, repeated mutations can lead to skin cancer.

Red light photons carry roughly one-tenth the energy of UV photons. They cannot ionize DNA or break chemical bonds. Instead, red light is absorbed by mitochondria—the energy-producing structures inside cells—where it stimulates an enzyme called cytochrome c oxidase. This increases the cell's energy production (ATP) without altering the genetic code. The cell responds by reducing inflammation and increasing repair processes, but the DNA itself is not damaged.

This is why red light is sometimes called "non-ionizing" radiation, a category that also includes visible light and radio waves. None of these can cause the direct DNA damage that leads to cancer.

What human safety data exists

Red light therapy entered clinical use in dermatology and wound care in the 1990s. Since then, it has been used in thousands of medical procedures, mostly for skin conditions like acne, psoriasis, and slow-healing wounds. Regulatory bodies including the FDA have cleared red light devices for specific medical uses, and dermatologists have monitored outcomes.

A 2019 systematic review in Photomedicine and Laser Surgery examined safety across multiple studies and found no reports of cancer or precancerous changes linked to red light therapy. Another 2021 review in Lasers in Surgery and Medicine reached the same conclusion. These reviews included studies spanning decades and thousands of patient exposures.

The strongest safety data comes from medical settings where exposure is controlled and monitored. Home-use devices, which have become more common in recent years, have less published safety data simply because they are newer and less formally tracked. This does not mean they are unsafe—it means the long-term effects of repeated home use have not been studied as thoroughly as clinical use.

Theoretical concerns that have not materialized in practice

Some researchers have raised theoretical questions about whether red light could potentially stimulate cancer cells that already exist, or whether it could increase skin cell growth in ways that might eventually lead to cancer. These are reasonable questions to ask about any therapy that increases cell activity.

In laboratory studies, red light does increase cell proliferation (growth) in normal cells, which is why it helps wounds heal. However, the same studies show that red light also triggers apoptosis—programmed cell death—in some cancer cell lines, particularly melanoma cells. This suggests the effect is not simply "more growth equals more cancer risk." The relationship is more complex and appears to depend on the type of cell and the dose used.

In human studies, no increase in skin cancer rates has been observed in people using red light therapy, despite the theoretical possibility. This gap between theory and observation is common in medicine and usually means the theoretical risk is either very small or does not occur in living humans the way it might in a petri dish.

Who should be cautious and why

While red light therapy appears safe for most people, certain groups should discuss it with a doctor before use. People with a personal history of melanoma or other skin cancer have a higher baseline risk of developing cancer again, and any new skin treatment should be reviewed by their dermatologist. Similarly, people with a strong family history of melanoma may want medical guidance, since genetic factors influence cancer risk.

People taking photosensitizing medications—drugs that make skin more sensitive to light—should also check with their doctor. These medications can interact with light therapy in ways that increase skin irritation, though the cancer risk remains low. Pregnant people should discuss red light therapy with their obstetrician, not because of cancer risk but because safety in pregnancy has not been studied.

People with thyroid conditions should avoid directing red light at the thyroid area, since some evidence suggests red light can increase thyroid activity. This is not a cancer concern but a general safety precaution.

What happens when red light is used on existing skin lesions

A specific concern sometimes raised is whether using red light therapy on a spot of skin that already contains cancer cells could make the cancer grow faster. This is theoretically possible with any treatment that increases cell activity, but it is not documented in the medical literature.

In fact, red light therapy is sometimes used as a treatment for certain skin cancers, particularly non-melanoma types, in a process called photodynamic therapy. In these cases, a photosensitizing drug is applied first, then red light is used to activate it and kill cancer cells. This shows that red light can be used medically against cancer, not just safely alongside it.

The practical takeaway: if you have a new or changing skin lesion, have it evaluated by a dermatologist before using red light therapy on that area. This is standard medical practice for any new skin treatment, not specific to red light.

The difference between home devices and medical-grade equipment

Red light devices sold for home use vary widely in power, wavelength, and safety features. Medical-grade devices used in clinics are typically more powerful and more precisely calibrated. Home devices are generally weaker and considered lower-risk, but they are also less formally regulated and less studied.

The FDA clears some red light devices as medical devices, which means they have met certain safety and effectiveness standards. Other devices are sold as wellness products with no FDA clearance. Neither category has been shown to cause cancer, but the cleared devices have more rigorous safety documentation.

If you are considering a home red light device, look for one that specifies its wavelength (ideally 600–1000 nanometers) and power output. Devices that are FDA-cleared for a specific use have more published safety data than uncleared devices. This does not mean uncleared devices are unsafe—it means the evidence base is smaller.

Frequently Asked Questions

Can red light therapy cause melanoma?

No. Melanoma is caused by DNA damage from UV light, and red light does not carry enough energy to damage DNA. No cases of melanoma have been linked to red light therapy in medical literature, despite its use in thousands of patients over 25 years.

Is red light therapy safe if I have had skin cancer before?

You should discuss it with your dermatologist first. While red light itself does not cause cancer, people with a history of skin cancer have a higher baseline risk, and your doctor may want to monitor any new skin treatments. They can advise based on your specific type of cancer and risk factors.

What if I use red light therapy and later develop cancer?

Developing cancer years after using red light therapy does not mean the therapy caused it. Cancer has many causes and usually develops over years or decades. If you are concerned, your doctor can review your medical history and any risk factors. Reporting the timeline to your doctor helps them understand your full picture.

Are home red light devices less safe than medical ones?

Home devices are generally weaker and therefore lower-risk, but they are less formally studied. Medical-grade devices have more published safety data because they are used in clinical settings where outcomes are tracked. Neither type has been shown to cause cancer, but medical devices have stronger evidence of safety.

Can red light therapy make an existing cancer grow?

This has not been documented in humans. While red light does increase cell activity, it also triggers cell death in some cancer cell types. If you have been diagnosed with cancer, discuss any light therapy with your oncologist before use, but the cancer risk from red light itself is not established.