There are several causes for this condition but the most common are inflammation of bladder due to germs, allergic reaction and friction.
BACTERIAL GERMS : In women the entrance of the urine and anal passage are very close so bacteria can easily travel into the bladder and multiply there to cause its inflammation. Trauma as in "Honeymoon Cystitis" following unaccustomed and rather prolonged or vigorous sexual activity , insertion of tampons, wiping your bottom from back to front or wearing tight trousers can push the bacterial germs into the bladder.
NON -BACTERIAL : Common non - bacterial vaginal infection like thrush can give symptoms similar to cystitis. Germs that are sexually transmitted like Herpes and Trichomonas are also sometimes responsible.
OTHER CAUSES : These include allergies to toiletries and like vaginal deodorants, perfumed soap or talcum powder. Anxiety or depression and a condition called "Irritable Bladder " can also be responsible for the condition. Radiation, eg after radiotherapy to other organs in the pelvis.