Sunlight energizes your immune system

New evidence out of Georgetown University suggests that sun exposure — even in the dead of winter — can help you fight off colds better and faster. Let me explain…

When we talk about sun exposure, most people think about ultraviolet B (UVB) wavelengths. UVB wavelengths are invisible to the human eye. And they also activate vitamin D production in the skin. (And as you know, vitamin D helps fight virtually every disease, including infections.) So most of the research on sun exposure has focused on the UVB ray-vitamin D connection.

But for this study, researchers studied a different part of the spectrum — the blue light found in the sun’s rays. Blue light comes from the visible spectrum of solar radiation, and it had been studied in Europe for its healing effects.

The Georgetown researchers found that blue light of the sun reaches through the top layer of skin and activates T-cells in your immune system, telling them to move throughout the body.

(T-cells help kill microbes. And they reach the site of infection by circulating through the blood. Interestingly, the skin hosts approximately twice as many T-cells as found normally circulating in blood. There is a strong connection between the skin organ and the development of the immune system.)

How exactly does it work?

Without getting too complicated, blue light from the sun increases synthesis of hydrogen peroxide. This synthesis then activates a signaling pathway, increasing T-cell movements.

White blood cells in your immune system also release hydrogen peroxide when they come into contact with a microbe to kill it. The release of hydrogen peroxide “calls” more T-cells and other immune cells to recruit them to the site of infection to mount a full immune response.

It all makes perfect sense. And it’s one more good reason to spend more time in the sun without sunscreen.

Furthermore, UVB rays that activate vitamin D only penetrate the atmosphere when the sun is high enough, from April through October, in most parts of the U.S. By comparison, blue light reaches the Earth whenever the sun is shining — 12 months of the year. So you can get your infection-fighting blue light rays year-round by going out in the sun.

Maybe the cold and flu season has something to do with not getting enough of the sun’s blue rays on your skin during the winter?

Researchers in Georgetown’s Department of Pharmacology and Physiology — the same department where I serve as an Adjunct Professor — published this study last December 20, just in time for the annual winter solstice, the day when the diurnal duration of sun light is the shortest of the year.

If you’ll excuse me now, I am going out to get some sun. Make sure to get some yourself this weekend.


  1. “Intrinsic Photosensitivity Enhances Motility of T Lymphocytes,” Scientific Reports 12/20/2016; 6: 39479