I have developed postnasal drip, constant clearing of throat, and cough for 8weeks now. I went to my GP who thought it was due to seasonal allergies even though I’ve never been tested for allergies before. She told me to use a nasal saline spray and then use Nasacort, Which I’ve been doing for the entire eight weeks. About six weeks ago I saw an allergist and got tested and nothing Lit up for allergies so the doctor thought I perhaps have environmental allergies and not seasonal allergies. He told me to stay on the same treatment that my GP said. I am absolutely miserable and now my nose is raw inside. I am a CPAP user and have never used the humidifier. Can post nasal drip be caused by not using my humidifier on my CPAP?

Welcome to the forum.

Honestly I am not sure, but assuming you have a humidifier on your PAP machine, you can turn it on at a moderate level and try it. If for example, it is a ResMed 10 PAP, your humidifier is built-in and only needs the tub filled with water and turn it on. Typically, other machines have the humidifier as a piggy back add on. If your house water is drinkable, it may be used in the humidifier though most PAP manufacturers state distilled water. I have used my ResMed for 2 years with tap water after 1 year of distilled. There's not much difference, just maybe rinsing the tub more often with tap water usage.

_________________
Duct tape carrying K9; the tape helps quiet stupid.
Dave K9DWB 73s

https://www.sleepfiles.com/OSCAR
http://www.apneaboard.com/wiki/index.php/OSCAR_Help
http://www.apneaboard.com/wiki/index.php/OSCAR_Chart_Organization

Yes, not using added moisture to the cpap air can sure mess with the nasal mucosa.
Google "cpap rhinitis".
The reason we have humidifiers routinely prescribed with cpap is for this very reason. What machine are you using?

Distilled water helps prevent mineral accumulation in the water chamber but you can use tap water or bottled drinking water.
The worse thing that will happen is some mineral build up inside the water chamber and it is easily removed with a vinegar or lemon juice soak. How much mineral build up will depend on how hard your water is.
Some people don't have any build up but some people have a lot because their tap water has a high mineral content.

_________________
I may have to rise but I refuse to shine.

I've had Postnasal drip since before CPAP. I take claritin daily and flonase, 1 spray twice a day. I try just one spray now and then but usually have to go back to twice a day pretty soon.