system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does it hurt to wash my nostrils with pure water while salty water is fine?
gpt
The insides of your nostrils (sinuses) are lined with mucous membranes, which are made of cells which are filled with slightly salty water. Water can flow through cell walls through osmosis, and in such a situation the water flows in a way that equalizes the cell's salinity (salt level) with the water around it. So when you pour unsalted water in your nose, the millions of cells suck up the less-salty water and end up bursting. Ouch!!! If the external water has equal salinity, the water doesn’t flow either way and your cells remain intact. Ahhhhh…..