More than one million Australians may be compulsive hoarders, a conference heard on Tuesday night.

Psychologist Dr. Christopher Mogan also said compulsive hoarding disorder is five times more common than schizophrenia and twice as common as obsessive compulsive disorder (OCD).

"Obsessive Compulsive Disorder is already the fourth most common mental disorder... it's really a sleeping giant," said Dr. Morgan, who spoke at the 2-day forum, called Pathways Through the Maze National Hoarding and Squalor conference.

Catholic Community Services has calculated more than one million Australians could be suffering from the signs and symptoms of hoarding.

Director Annabel Senior said a study revealed that many rental tenants were at risk of eviction because of their unpleasant hoarding habits.

The conference was attended by 135 experts from Australia, the UK and the US.

Compulsive hoarders are so irrationally attached to things that it interferes with their relationships. They often live in unpleasant conditions and risk sickness and injury due to their collection spanning years, with hoarders often have no time to even sort through their collection.

"To throw something away is to throw away part of themselves ... it's a very pervasive disease that's hard for the non-hoarder to grasp," said Dr. Morgan.

Twenty years ago, compulsive hoarding disorder was regarded as a variation of OCD, but it should be classified as a distinct disorder with its own criteria, research, therapies and training for specialists, according to the psychologist, emphasizing that hoarding is "separate from OCD."

Meanwhile, Dr. David Tolin, director of the Anxiety Disorders Center at the Institute of Living at Hartford Hospital, said that even though compulsive hoarding is considered by many researchers to be a type of obsessive-compulsive disorder, compulsive hoarding may also be related to: impulse control disorders (such as impulsive buying or stealing), depression, social anxiety, bipolar disorder and certain personality traits.

During an episode of the defunct TV talk show Oprah, Dr. Tolin said people usually start hoarding during childhood and the problem usually escalates in adulthood.

Compulsive hoarding may run in families, and many hoarders usually fail to see they have a problem until a family member gets too upset by the clutter at their home, Dr. Tolin said.