How often should I use nasal sprays?

The number of times a day you can use a nasal spray is usually defined on the product packaging - look for the dosage instructions. Some people do find the need to use sprays a bit more than directed. This is not usually an issue as long as you don't go as far as doubling the dosage.
 
In general, use of sprays containing synthetic or chemical active ingredients are restricted to 7 or 10 days. The reason is that these drugs can cause a problem known as re-bound rhinitis, where symptoms worsen after stopping use.
 
However, use of nasal sprays containing natural ingredients such as menthol do not cause this problem and may be used for up to 30 days continuously.