Cystitis or inflammation of the bladder is caused by a bacterial infection, and is well known as urinary tract infection (UTI). It can be very painful and annoying, and can turn into a serious health problem if the infection reaches your kidneys.
The reason may be a reaction to certain drugs, radiation therapy or potential irritants, such as feminine hygiene spray, spermicidal jellies. It is even possible with the long-term use of a catheter, or as a complication of another illness. The ideal way to treat cystitis is antibiotics, while the treatment depends on the underlying cause too.