Shining a Light on Autoimmune Diseases: “The Sunshine Cure”

by Brian T Lynch, MSW

This is my summary of an essential article in Scientific American from June 2025. The article is called "The Sunshine Cure"; the discovery that sunlight boosts your immune system is leading to new disease-fighting therapies, by Rowan Jacobsen, et al.

Kathy Young of Virginia Beach was diagnosed with multiple sclerosis (MS) in 2008. MS is a disease in which her immune system attacks the protective sheath that insulates the nerve fibers in her central nervous system. Her symptoms included weakness, spasms, speech and vision problems, extreme fatigue, and what she called cog fog or low-grade cognitive impairment. Like most MS sufferers, her symptoms would sometimes flare up and then improve somewhat, but overall, her symptoms gradually worsened. For years, Miss Young was forced to rest in bed several times a day.

Today, she is among a small group of MS patients who bathe themselves briefly each day in an ultraviolet (UV) light box designed initially to treat psoriasis. Within a few months, her fatigue disappeared. Blood tests confirmed that her inflammatory levels dropped to low levels and remained there for over a year. She still has symptoms of MS, which is incurable and progressive, but she is better able to function, and her vitality has returned.

A few clinical trials on MS light therapy have been conducted, and early evidence indicates that UV light can calm an over-aggressive immune system. This may prove beneficial in treating symptoms in other autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis, Crohn's disease, and colitis.

Research conducted in 1974 found that UV light exposure on the skin of mice caused tumors to grow. UV light can damage a cell’s DNA, leading to cancerous cell growth. But when the cancerous tumors of UV-exposed mice were transplanted onto mice that were not exposed to UV light, the immune systems of the unexposed mice were able to kill the cancerous tumors. This led to the discovery that UV light causes tumors to grow and, at the same time, suppresses the immune system, allowing the tumors to continue growing.

The immunosuppression effect of UV light explained a long-known fact that sunlight seemed to improve psoriasis, another autoimmune condition. Furthermore, UV light treatment on one patch of psoriasis on a patient improved the condition of other untreated patches as well. This meant that the photochemical interactions in our skin produce beneficial substances that are distributed throughout the body. Photoimmunology became a new medical discipline. In laboratory experiments, photoimmunologists observed that the entire immune system of mice exposed to UV radiation switched to anti-inflammatory states. The trick is to strike the right balance of UV light exposure to suppress an overactive immune system without causing too much DNA damage.

Confirmation of the immunosuppressive impacts of UV light came when studies searched for correlations between various autoimmune diseases and geographic latitudes where patients lived. The closer to the equator a person lives, the more sun exposure they receive. The correlation was clear with most autoimmune diseases. The strongest link was with multiple sclerosis. The higher the latitude, the higher the incidence rate of MS, and MS patients reported more seasonal relapses. Another study compared sun damage on the back of a sample group's hand (a lifetime indicator of sun exposure) with MS cases and found that people with the most sun damage have one-third the rate of MS. Also, children who spend less than 30 minutes outside each day have twice the lifetime risk of developing MS compared to children who spend an hour or more outside daily.

In another small clinical trial, twenty patients with an early-stage version of MS were recruited. Half received UV light box treatment, and the other half did not. Within a week, blood tests on the treatment group showed a drop in inflammatory proteins that stayed lower even after the UV treatments ended. Three months later, the treatment group’s disease-severity scores fell 13 points while the untreated group’s scores rose by 14 points. A year after treatment, all who didn’t get the UV therapy developed full-blown MS, but 30% of the UV treatment group did not yet fully develop MS symptoms. It appears that UV light therapy not only calms the immune response in MS patients but also seems to reset the immune system balance.

UV therapy has positive implications for other autoimmune diseases as well as conditions related to chronic inflammation, such as Alzheimer's disease, arthritis, asthma, and some heart diseases. Exactly which photochemical compounds or combinations of compounds produce the beneficial effects remains unknown. It isn’t vitamin D3, however, as was initially believed (not that vitamin D isn’t beneficial). The difficulty arises from the many molecular byproducts that UV exposure produces in our skin. There is much more to learn, and scientific studies are just getting underway in earnest. The big takeaway for now is the need to maintain a healthy balance of sunlight, whatever that may be. It is probably a different mix for each of us, but the extremes of sunlight and no sunlight should clearly be avoided.