It affects every single member of our community - if not directly, then someone they know. Chances are, we all have someone in our family and someone we work with who has experienced it.
One in four people suffer from it in any given year, according to the charity-led campaign Time to Change. It has damaging symptoms and consequences, including making it near impossible to hold down a job and alienating your friends and family.
In 90 per cent of suicides, this phenomenon is the main cause, says the National Health Service.
If it were a physical condition, the community would come together, funding would pour in and emergency measures would be taken. But those with mental illnesses are often treated as invisible, with their conditions misunderstood or even seen as character defects. Nine out of every 10 people with mental health problems experience discrimination as a result.
Naomi Glickman, a social worker for Jewish mental health charity Jami, says combating the stigma is an uphill battle. "We work with the community to get them to understand the issues of our clients. But often the families of sufferers still don't understand. People come and say they've lost support because others have found out about their mental illness."
Some see mental illnesses as a sign of weakness, while others treat them as a kind of homogenous, permanent insanity. Ms Glickman, who has been a social worker for 30 years and works at Jami's Redbridge centre, says these misconceptions can stop members of the community from seeking help.
"An Orthodox woman came to me and said she had psychosis and had never told anyone. She was in her forties, and she also had a child with mental health problems. She'd never felt able to talk about it with her daughter, or husband, or anyone. Mental health is still, in this close-knit community, something which people don't understand."
This is sometimes exacerbated by communal leaders. "I've had rabbis in Redbridge tell me: 'We don't have any mental health issues in the community,'" Ms Glickman revealed.
For Laurie Rackind, chief executive of Jami, this makes an already destructive problem even worse. "If you break your leg and we said you'll never walk again, we'll get you a wheelchair, everyone would think that was ridiculous, but that's what you're doing when you turn your back on people with mental health problems. The stigma is such that it still prevents people from engaging with services, which is a shame because their lives can be so much more positive and recovery is possible for most people if they get the right help."
Attitudes about illnesses such as psychosis (closely associated with violence), schizophrenia (confused with multiple personality disorder) and depression (disregarded as sadness or even laziness) have not evolved enough in recent decades.
Mr Rackind says the problem is heightened in the Jewish community by self-inflicted pressures. "Because we put such focus on success and achievement, anything that potentially takes away from that - like mental illnesses - we have a tendency to sweep under the carpet.
"Considering that we're at the forefront of providing social care and physical care, it's very ironic that we should be anything apart from ahead of the curve in engaging with mental health care. We're famous for talking about our physical ailments, which doesn't do any good, but we don't talk about our mental health issues, which actually would help."
Jami is providing an invaluable service to a group which still largely attempts to ignore the problem, even with cuts in government funding of 8.25 per cent over the past five years. "We run on a shoestring," Ms Glickman said.
The charity's holistic approach helps people to reintegrate with the community, get a job and reconnect with friends, as well as educating everyone else about mental health.
Time to Change says almost three out of every four young people fear the reactions of friends when they talk about their mental health problems.
But Mr Rackind has a more optimistic view: "Breaking down the stigma comes down to education. For older people it's still a taboo, but the work we do in schools has demonstrated to us how much more prepared younger people are to talk about their mental health, and that's great for the future."