Decongestant nasal sprays can help reduce nasal congestion caused by a condition that irritates or inflames the sinuses — such as allergies, a cold or the flu. But after a few days, the lining of your nose may become less responsive to the medication. You may need more and more nasal spray to control congestion. If you stop using the medication, your congestion may get worse. This is known as rebound congestion. What's the fix? If you have rebound congestion, stop using the spray and wait. Call your doctor if you need help. To prevent rebound congestion, use decongestant spray for no more than a few days in a row.