Its owner, a 79-year-old Melbourne woman, had been admitted to hospital and a social worker and occupational therapist decided to visit her home in preparation for her discharge. Meal on Wheels containers piled up in the fridge of a 79-year-old Caulfield woman. They found rooms buried in rubbish-filled plastic bags. Orange cigarette butts littered the ground like confetti. There were hundreds of Meals on Wheels containers – dozens of empty ones stacked together, and others, still with food in them, packed into the fridge and placed in piles on the kitchen floor. At some point it appears the woman's toilet had stopped working, so she had started using a cardboard box, which was by then overflowing with paper and faeces.

The workers had stumbled across a squalid household. The home of a 79-year-old woman from the Caulfield area who had been living in squalor. Severe domestic squalor is not a distinct medical condition, but rather is described as a living environment that has become so unclean, messy and unhygienic that people of a similar culture would find cleaning and clearing essential. Over the years there have been various theories on what causes squalor – including that it was linked to personality disorders. Husband and wife team Steven Penn and Lorinda de Regt-Penn run a forensic cleaning team that works in squalid properties. Credit:Simon O'Dwyer

But a recent Australian study, the largest of his its kind, has come to a new conclusion that has huge implications for how cases of squalor should be treated. It tested 69 people living in squalor and found almost all the participants had frontal executive dysfunction. Brain damage, in other words, through dementia, head injury, alcohol abuse, stroke and other causes. Rubbish piled up in the house of an elderly woman in the Caulfield area. Her family had no idea of the conditions. You can't manage a problem without adequately assessing it. Associate Professor Steve Macfarlane The Melbourne researchers believe people's indifference to their living conditions stems from that damage to the frontal part of the brain, which controls planning, self-control, social interaction, judgment, problem solving and, crucially, insight.

It may be a hard to believe that a person living amid their own excrement would not realise there was something wrong with that. But that is exactly what typically happens in many cases of squalor – they don't see what others see. In trying to explain this absence of insight, the study's co-author Associate Professor Steve Macfarlane recounts his first squalor case. The patient was an animal hoarder living in country Victoria who had become unpopular with his neighbours by rattling up and down the street at 3am with a shopping trolley full of cans. The man's eight cats would go to the toilet in the house. His solution, which he considered perfectly adequate, was to cover the droppings with kitty litter and leave them there in piles. The cat hoarder had congenital hydrocephalus, a swelling of the head through the build-up of fluid in the brain. "If you turned the light off and put a torch against [his skull] it would glow red, because it was fluid filled," Professor Macfarlane said. "So that was his frontal lobe impairment."

Squalor does not just appear overnight, but develops over many years, perhaps decades, in layer upon layer of food left to rot, spider webs that thicken in corners and all manners of animals that come and go. "One of the tragedies is we're still stumbling across people living in squalor which has obviously taken decades to accumulate and people are left to get to that point," Professor Macfarlane said. Some of this inaction is driven by a view that people should be free to live the lifestyle of their choice, or in some cases, an unwillingness to interfere or be impolite. Steve Penn and Lorinda de Regt-Penn, a husband and wife team behind forensic cleaners TACT Bio-Recovery, once visited a Melbourne unit where the owner had incrementally filled the whole bathroom, above the height of the toilet, with used panty liners. Mr Penn said the lady living in the flat had asked her neighbour whether she could smell anything when she walked past.

"The neighbour said 'no I can't'," Penn says. "We could smell it from the street. "The neighbour confided in us that she didn't want to embarrass her. They had lived side by side for 30-odd years." Professor Macfarlane said people in putrid living conditions had often been managed by "well-meaning service providers" for many years. "The person has been saying to their care provider, 'I don't want anything done to this place, I'm quite happy here' – that's accepted at face value," he said. However, the newest research suggests it is no longer acceptable to tolerate squalor as a "lifestyle choice".

"While it might be conceivable for a person to truly wish to live in unsanitary conditions, such cases are likely to be extremely rare, and it is more likely that squalor represents a loss of capacity," the Melbourne researchers concluded. Somewhat controversially, a solution may have to be forced. Guardians can be appointed on behalf of a person to arrange ongoing clean-ups of a squalid home or, depending on the circumstances, a move into residential care. "They have kicked and screamed to the point of going, but once they are actually there, they do really well," Professor Macfarlane said. In 2014 an elderly man was found unconscious in his home, following a fall. He had spent three days lying in animal and human faeces, with a fractured femur and leg sores. It was discovered that his properties – two shops with a houses attached in Melbourne's western suburbs – were so squalid and cluttered it would take an industrial clean worth $70,000 to bring them back to habitable conditions.

But the man was resistant to help and advice. In a Victorian Civil and Administrative Tribunal hearing three months ago, his lawyer said he had "always lived in squalid conditions, but those choices are not related to age or disability, and he should be free to live the way he chooses". Medical experts disagreed, finding he lacked insight into his situation and could have dementia. According to court documents, he told neuropsychologist Sophe Kimonides the "mess" was made by other people while he was in hospital and that, at the age of 93, he might travel to Cyprus to look for "job opportunities" and "perhaps marry and have child". The tribunal member ruled in favour of appointing a guardian to manage his accommodation and help him return home. While front-line community workers instantly recognise a squalid household, people living in filthy homes often fly under the radar because they otherwise appear normal and presentable. When a foul-smelling green slime was discovered leaking from the ceiling of an upmarket inner city apartment, a police officer and psychiatrist were dispatched to stake out the address.

The property above was found to be knee-deep in bottles which its owner had collected with the intention of recycling, but never got around it, while pigeons were fluttering through the kitchen window, pecking at the discarded food. After three nights, authorities finally intercepted the owner returning home from work late in the evening. She was a neatly dressed professional woman who worked full-time in a client services job. Her bad breath was the only thing that marked her as different – and even that was not apparent from a distance. It is estimated that up to 1 in 700 Australians over 65 are living in domestic squalor, or about 5000 people. Hoarding – a condition that can see people fill their houses up to the roofline with possessions – can also result in squalid conditions, as kitchens are hijacked by junk and food is left to go off. However, unlike squalor, hoarding is a distinct mental disorder that should not be addressed with forced measures. Hoarding is thought to have its roots in genetic factors and past loss, grief and trauma. These issues need to be addressed before any clean-up takes place.

Melbourne psychologist Chris Mogan has seen people turn their homes into a virtual museum following a bitter divorce, leaving everything as it was before the marriage broke down. Dr Mogan said people with hoarding disorder saw themselves – and their memories, identity and attachments – in their possessions. "So taking their things away from them is literally like pulling their fingernails off," he says. Extreme hoarding, including cases where people have been tunnelling animal-like through their homes, are often named by front-line workers as the most disturbing sights they come across. De Regt-Penn says she has been in a property where she was forced to climb over piles of sloping rubbish, which rose to leave only a small gap at the top of each door to squeeze through. "It was almost like the person was a bowerbird and was making their nest – that's how I can explain what it was like," she says. "It's like an indoor tip."

One of Australia's most high-profile squalor cases was intermeshed with hoarding. A family home in Melbourne had been transformed into a fetid dumping ground, with a thick layer of hoard, including dirty toys and food packaging, smeared with faeces. The sickening conditions led to the 2012 death of the five-year-old boy after he cut his toe on an open can of cat food left lying in the home. The family had been invisible to authorities, never having come to the attention of social workers. Tragically, researchers say it often takes a "crisis situation", such as a death, fire or hospital treatment, for extreme squalor to come to light. Almost one-quarter of fatal residential fires are linked to hoarding and squalor, according to a Melbourne Metropolitan Fire Brigade study. Meanwhile, a 2014 audit of Caulfield Hospital patients found that, at any one time, up to 12 patients were awaiting an industrial clean of their home.

Severe insect bites saw a Melbourne woman admitted to hospital in November 2014. It was later discovered her $2.5 million to $3 million home was infested with fleas and bedbugs. Photos taken of the property suggested the 76-year-old could have been living in squalor for years, with every surface buried in paper, crockery, clothing or open food containers. The woman had previously had a notable professional career before being diagnosed with frontal lobe dementia. Professor Macfarlane said there is a need for a national protocol to ensure people living in squalor received the appropriate psychiatric assessment before the point of crisis. He said that protocol should co-ordinate all the agencies that might come in contact with patients, including councils, home care providers, general practitioners, Meals on Wheels services and district nurses. "You can't manage a problem without adequately assessing it and that's where the current system falls down." It is likely there are many Australians living unnoticed in squalid homes.

Professor Macfarlane said it was important people did not turn their backs on the neighbours, or wait "for the rats to move in" before contacting authorities – be it the local council, police or fire brigade. "There is a quote that goes something along the lines of 'to respect the decision of someone who has capacity is to empower them, to respect the decision of somebody who lacks capacity is to abandon them'." "In many ways I think it is societal abuse, with society not being prepared to act to remove these people from dire circumstances."