Over one million Australians may be compulsive hoarders, a conference has heard.

Compulsive hoarders often live in squalor and risk disease, injury, fires and homelessness, and their over-attachment to things can compromise their relationships, clinical psychologist Dr Christopher Mogan says.

"To throw something away is to throw away part of themselves ... its a very pervasive disease that's hard for the non-hoarder to grasp," he told a conference in Sydney on Tuesday.

The two-day forum, dubbed Pathways Through the Maze National Hoarding and Squalor conference, attracted 135 experts from Australia, the UK and the US.

According to Dr Mogan, compulsive hoarding disorder is five times more common than schizophrenia and twice as common as obsessive compulsive disorder (OCD).