Sinus cleansing (an Ayurveda procedure aimed at irrigating your nose in order to re-establish the right osmotic balance in the nasal mucosa) can hugely help allergy sufferers (especially in spring) and people with frequent sinusitis.
This is what you need for the nasal cleansing
A neti (Sanskrit for “nasal cleansing”) pot (can be of different sizes, shapes and materials but they all look more or less as the one below)
One cup of water with a tablespoon of sea salt (It is advisable to always use distilled, filtered, bottled or boiled water at room temperature – tap water may contain bacteria which may be dangerous for your nasal mucosa)
… and this is what you should do
Fill the neti pot with water and dilute the salt in it. Pour the salt-water solution into one nostril and let it run out through the other one while keeping the mouth open to breathe (use gravity as an aid). Repeat with the other nostril and then keep alternating between nostrils, until all the solution in the cup is used.

People suffering from chronic sinusitis should also try to avoid as much as they can Sugar, White Flour, and Milk (all dairy products).