Many things: Several possibilities: age, surgery, inflammation, radiation, chemicals, infection -- and many times it just happens as people age, without any obvious cause, or it isn't worth looking for the cause, since the treatment is so easy and effective.
Answered 7/23/2013
5.2k views
5 doctors weighed in across 2 answers
4 doctors weighed in across 2 answers
6 doctors weighed in across 2 answers
90,000 U.S. doctors in 147 specialties are here to answer your questions or offer you advice, prescriptions, and more.
Ask your question