There is a nasal cavity in the human nostrils. There is a thin and tender mucous membrane on the surface of the nasal cavity. There are many very thin blood vessels on the mucous membrane. When you pick your nose with your hands, the sharp and hard fingernails can easily tear the mucous membrane and bleed. In addition, if the mucous membrane is scratched, germs will penetrate into the small blood vessels, and the nostrils will become red, swollen and inflamed.

There are also many small hairs in the nostrils, called nasal hairs. Nose hair is also very useful. When you inhale, it can filter and retain dirt in the air. If we pick out our nose hairs, dirt will be sucked into our bodies, which can also make us sick.