I don’t have any irritation, but I’m a big robust guy, so perhaps milage may vary.
And sure, I would assume that the sinuses are self-cleaning to an extent, but they are also designed to be a filter to keep junk out of our lungs. The way I see it, I’m just cleaning the filter out before I go to bed.
Warm salt water. That makes sure that the water is not pulling salt out of your cells. Doing it without salt is painful and dangerous. Also the salt should be without iodine added.