My cousin is a severe hoarder. After becoming aware of the problem, I've been shocked to realize how many other hoarders I know. My aunt's mother, whom I boarded with for three weeks, a colleague of mine who was a good friend, my apartment mate/exercise partner/co-worker and a long term family friend as well are the people I've been closest to, although I know of many others.
Often hoarders end up with someone who is either a spender/buyer (usually to cope with emotional pain, much like comfort eating), or else someone who is a saver/hoarder themselves. Often weight is an issue for hoarders as well. And mostly hoarding appears to be rooted in emotional issues: loyalty towards a parent who hoarded (often made worse after that parents' death as a way of honouring their memory), living in a traumatic, emotionally chaotic environment, nostalgia about the past and needing tangible reminders of it all around, living through conditions where there wasn't enough provision for needs. Sometimes having a lot of animals is one area where the hoarding occurs.
In the case of the couple I worked with, she bought enormous amounts of food (they had a room of their house up north and a couple rooms down south, plus their kitches absolutely crammed with food. She also had excessive amounts of clothing. Her husband had grown up with very little and he had a huge need to reclaim any bit of junk that he could. When they finally moved from the north, he actually purchased a school bus to contain some of his stuff. The thought of selling anything was very painful to him because he thought he might need it. He also had a collection of cars that didn't work well. (I believe he has 10 licenced vehicles right now for the two of them!). She had a weight problem and many, many health complications. He didn't, but had a mother who hoarded.
My aunt's mum was a chronic garage saler. Every room was jammed with furniture and other items. She had all of the walls in the basement devoted to food and yarn, both freezers were overflowing with meat (she was in her early 80s and lived alone) to the point where they wouldn't close, the cupboards and fridge upstairs were also filled so full that they wouldn't close. She had had an alcoholic husband who was habitually cheated for years and finally left the family altogether. I don't know what her childhood was like. Weight was an issue for her.
With our friends, she spends inordinate amounts of money on shopping trips, candle/Arbonne/Pampered Chef and a million other kinds of home parties for friends, eating out, trips, clothes, and replacing items that she cannot find. She's frustrated with her husband, who lost two parents in the last few years who were hoarders. He was bad before, but it's reached epic proportions now. They have two whole rooms that are filled with important mail, junk mail, clothing, books, swimming suits, dress clothes, kitchen items, makeup etc all in a jumble. Much of it is still in the packages and hasn't been looked at. Her husband goes to library sales and thrift stores and has filled the garage to overflowing, and stores books in a car outside (secretly, until she discovered it). He gets upset if she even throws out a piece of string that he things could be useful later. They also have 2 dogs and 2 cats, none of which they have much time or attention for. All of his brothers also hoard. She had a difficult childhood which included sexual abuse and she has had chronic weight issues, even getting gastric surgery. He is of normal weight, but doesn't get around to doing anything. He works, but their house is falling down around them, they can barely get up the steps without falling through, but he's resistant to fixing the problem.
My friend and apartment mate had most of her childhood and everything since stuffed into a very small area. She too has many rubbermaids filled with a jumble of everything from important mail to garbage. She has cats which are very messy and she doesn't clean up much after them. Her house is so cluttered that it is almost impossible to straighten up or make the place orderly. She had a very difficult childhood, was sexually abused, a brother committed suicide, her father was violent and unpredictable and eventually abandoned them and her family is still very emotionally abusive to her.
In the case of my cousin, she ended up marrying a 19 year old Scottish man from a very dysfunctional background (apprehended from home with deaf, alcoholic parents, separated from siblings, in a home for violent children, adopted by a woman in her 30s, left home at 16, went on drugs etc). She was 30 at the time. Her self-esteem was low and their decision to marry was very quickly made. As she got to know him better, it became apparent that he was bi-polar, he cheated on her habitually, he was violent and unpredicatable, and he was physically and verbally abusive to her and their two children. He at last abandoned them after about 17 years together. She was not a hoarder before (actually was a good housekeeper and very orderly), but it slowly grew worse throughout their marriage. Even on the occasions where she has requested help, she then gets extremely angry if anyone throws out even obvious garbage (flyers from 2001 etc) and requests them to leave. Her new husband is also a hoarder and owns several houses. When one place gets too bad, he just goes and watches TV elsewhere. They have many mice cohabiting with them, but are unwilling to do the cleaning to eradicate them. They have a large collection of cars (19 last I remember) and have received several citations from the town for not cleaning them up. There are just small pathways linking each room together. There are dishes rusting in the sink.
In every case, these people have had their houses cleaned up by others. Sometimes it's willingly, sometimes not. In every case, it has reverted back to the same problem very quickly. Even when there's a lot at stake like children refusing to bring their grandkids into that environment to visit, the people do not change. Loved ones talking to them about it just provokes an angry response. Usually important paperwork is ignored for years on end and it costs an incredible amount of money. In every case (other than my cousin), these are people who work as professionals and are good at what they do. I'm not sure how the emotional issues associated can get resolved (I understand the rate of recovery is very low), but I think the hoarding is only an outside symptom, not the problem itself.