Sunlight’s UV-A rays might help your blood vessels relax by turning a substance in your skin called nitrite into nitric oxide, even without your body using its usual method—this could be why you feel that warm, tingling sensation in the sun.

When your skin is exposed to sunlight, the tiny cells near your blood vessels release a chemical that helps your blood vessels widen, just like the skin cells do—this might be why your skin turns red and feels warm in the sun.

When your skin is exposed to sunlight, nitrite in your skin—not nitrate—turns into a helpful molecule called nitric oxide that may improve blood flow. Scientists found this happens best when the light is UV-A and the nitrite is in a specific form.

When your skin is exposed to sunlight, it releases a natural substance called nitric oxide that helps calm down harmful molecules in your skin and keeps things balanced — but this doesn't work right if you have long-term skin inflammation.

When there's less sunlight in winter or far from the equator, your skin makes less nitric oxide from sunlight, which can upset the balance in your skin and make conditions like psoriasis or eczema worse.

Certain types of sunlight, specifically a narrow band of UV light between 340 and 370 nanometers, can trigger a helpful chemical reaction in your skin that releases nitric oxide — which might one day be used to treat health problems.