Wikipedia
Nose-blowing
Nose-blowing is the act of expelling nasal mucus by exhaling forcefully through the nose, usually into a facial tissue or handkerchief. In some cultures, blowing one's nose in public may be considered a breach of etiquette.
Nose-blowing may be used to alleviate nasal congestion or rhinorrhea (runny nose). A 2000 study showed that nose-blowing produces a high degree of pressure in the nasal cavities and may worsen a cold by propelling nasal mucus into the paranasal sinuses.