What causes hoarding and how is it treated?

It's Complicated. For a thorough answer to your question, check out this page on the website of the international ocd foundation: http://bit.Ly/kqv4tl and for a sensitive look into the lives of people struggling with hoarding, see matt paxton's book "the secret lives of hoarders." hear matt speak about his book here: http://bit.Ly/lrdg78.
OCD. Could be a symptom of obsessive-compulsive disorder. Is a treatable condition. Rec. Talk to your pcp, mental health provider and social worker to improve the quality of life.