There are about 310,000 of them in WA and more than 2.5 million Australia-wide - and they're saving the Government a bundle.
If the unpaid carers sprinkled liberally throughout the towns and suburbs of Australia were to be paid for what they did it would bankrupt the nation, according to mental health carers' advocate Mike Seward.
"They have a very central and important role, one that is often overlooked and definitely undervalued," he says. "And it's done free of charge, out of love."
Not only that, but they're doing it at considerable risk to their own physical, emotional and financial wellbeing.
Numerous studies have pointed to the stress carers experience as they attempt - many working around the clock every day of the week - to meet the needs of loved ones who may be incapacitated by anything from age and dementia to mental-health issues, congenital disabilities, acquired brain injuries or other disabling conditions.
Liberal MP Craig Kelly, debating a motion about the proposed National Disability Insurance Scheme in Federal Parliament last week, likened the stress levels of single mothers of children with severe disabilities to those of combat soldiers.
Mr Kelly, who has a 16-year-old son with Down syndrome and autism, said he personally understood that for parents caring for a physically or intellectually disabled child, it was a lifetime's task.
"I understand that for most carers there are no days off, there is no sick pay, there is no holiday pay and there is no superannuation," he told Parliament.
"When carers grow old, they do so with the worry about what will happen to their children when they are too old or frail to nurse them. Many parents I know with kids with severe disabilities are on medication for depression. Divorce rates are high and studies show that single mums who have kids with severe disabilities have the same stress levels as soldiers in combat."
Reports from the Australian Bureau of Statistics and other organisations highlight the financial disparity between carers and non-carers, with carers less likely to be employed than other people, with their career prospects, superannuation and other savings suffering as a result.
If they are employed, they tend to work fewer hours. At the same time, many face significant care costs, with extra money needed for medication, equipment and appointments.
Carers can also take a hit socially and emotionally, experiencing feelings of grief, loss, resentment, loneliness and isolation as relationships, friendships and their own health suffer. Many carers report satisfaction with the role and a closer relationship with the person they're caring for but, for others, anxiety and depression can be a hazard.
"It's a little-known fact that families and carers of people with mental-health issues have higher instances of depression and anxiety than people with mental-health problems themselves," says Mr Seward, who is the executive director of Mental Health Carers Arafmi (WA) Inc.
He says much of the stress centres on the struggle to get appropriate and timely services and support, with carers faced with a labyrinth of bureaucracy as they champion their loved one's needs.
"There are challenges in dealing with the various machines of bureaucracy and with funding. Stuff that is funded by one arm of government will require things to happen in one way and stuff funded by another arm will require different things."
Paul Coates, chief executive of Carers WA, says carers face a period of huge change, with a raft of health reforms, including the National Disability Insurance Scheme, the introduction of Medicare locals, and mental health and aged-care reform set to have a significant impact on carers across the board.
"The defining issue for carers is the impact that these health reforms will have on their lives and whether these reforms will provide more support for carers or less," he says.