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.

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.

Sunlight can create harmful molecules in your skin, but your body naturally produces nitric oxide to balance them out—this balance keeps your skin healthy.

In people with certain skin conditions like psoriasis and eczema, their bodies make too much of two harmful chemicals that combine to create a damaging substance, which throws off their natural balance and weakens their body’s ability to protect itself.

Some light-based treatments might help calm down angry, inflamed skin by copying how sunlight naturally balances certain chemicals in your skin, which could make conditions like eczema or psoriasis feel better.

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.