Humidifier for runny nose?

My son has had a runny nose for about a week and I was wondering if a cool most humidifier would help with that? Or does it only really help for stuffy noses? 
He doesn't have any other symptoms going on (like a fever, cough, anything like that) so I think it's just allergies. But I can tell it's bothering him because he's constantly rubbing it.