Allergies can lead to infection. When the lining inside the nose is exposed to substances to which a person is allergic, the lining swells. The swelling blocks the drainage openings of the sinuses, leading to mucous accumulation. As mucous lies trapped, it becomes infected, leading to sinusitis. Controlling allergies with medicines or allergy shots can treat the symptoms and may prevent sinus infections. People who have suffered from long term allergies may have tissue damage that leads to chronic sinus infections. In this instance, sinus surgery can remove thickened obstructive tissue which prevents nasal drainage.