How many times in a year should i use nasal deongestant spray safely? why does it give temporory relief only?

Everything changes: and everything returns. If the underlying condition remains (allergy) but the medication leaves, then the relief is temporary. Giving stress hormones causes the area to get used to HIGH amounts, and NOT respond to normal levels (tolerance, addiction) and have even worse congestion when the spray isn't there. This is most likely with use close together. It's times in a week not year.