Sinusitis usually follows allergic rhinitis. The swelling caused inside the nose due to the allergy causes blockage of the sinus drainage leading on to sinusitis. If you control the allergy by using nasal sprays, & antihistamines, the onset of sinusitis can be prevented to a good extent. Once the sinusits sets in, the initial stages can be controlled with saline nasal washes, & steam inhalation. If still not under control, an ENT surgeon should be consulted.