When you're aroused, the blood vessels in your genitals dilate and the tissue swells, allowing for increased blood flow. But it turns out, that swelling happens above the belt too — including in the nose. Structures in your nasal passages called turbinates, which help filter the air you breathe, puff up. During sex, though, your body produces adrenaline, which constricts your blood vessels to reduce blood flow again, causing your turbinates to shrink. “Since your nose is getting less blood flow, there’s less inflammation,”Dr. Benninger says. “That means your nose can open up and it’s easier to breathe.