While 鼻涕 itself is just a biological reality, the social customs surrounding it differ between China and the West. In many Western cultures, it's considered hygienic and normal to blow your nose decisively, even loudly, into a tissue to clear the nasal passages. Sniffling is often seen as annoying or unhygienic. In China, the opposite can be true, especially among older generations or in more formal settings. Blowing one's nose loudly in public, particularly at a meal, can be seen as impolite and disruptive to the group harmony. It draws attention to a bodily function that is considered private. Therefore, it is more common to see people sniffling or excusing themselves to a restroom to blow their nose discreetly. This reflects a cultural value of not imposing one's personal discomfort on the shared public space. While this is changing with younger generations, being mindful of this etiquette is wise.
鼻涕 is a high-frequency word used in various everyday contexts.
The term's connotation is overwhelmingly neutral and descriptive. It is not a rude or vulgar word.