There are four basic types of nasal spray; three of the four types are able to relieve some allergic symptoms, and the fourth can both prevent and relieve allergic symptoms.
Antihistamine nasal sprays are useful when it comes to relief from itching, sneezing, runny nose, sinus congestion and postnasal drip. They work by blocking the histamine that's released as your immune system attempts to fight off the allergen that caused the allergic response in the first place. The histamine is what dilates the blood vessels in your nose and sinuses to cause swelling, redness and itching. The downside to antihistamine nasal sprays is side effects: You might find yourself with a bitter taste in your mouth or a dry mouth. You can also become dizzy, drowsy, fatigued or nauseous. Some people get a headache, a burning sensation in their nose, a nosebleed or a runny nose.
Nasal sprays also come in the form of a decongestant. As the name implies, they reduce the congestion in your nose and sinuses. The side effects associated with decongestant nasal sprays are burning, stinging or dryness in your nose, a runny nose or sneezing. They can also cause irritability, irregularity in your heartbeat, dizziness, insomnia, tremors, anxiety and high blood pressure. They aren't recommended for everyone. You shouldn't use a nasal decongestant spray for more than a week at a time or it will end up leaving you with more congestion than you started with. Saline nasal sprays don't actually contain any medications, but they are available over the counter and can loosen mucous and relieve mild congestion.
The fourth type of nasal spray is the corticosteroid: It can both prevent and alleviate allergic symptoms when used regularly. Available by prescription only, it takes care of inflammation, congestion, sneezing, runny nose and itching. The side effects are a bad smell or taste in your mouth, irritation of the nose and nosebleeds.