Schizophrenia and dissociative identity disorder can sometimes be confused or mistaken for one another.

In reality, there are many differences between the two conditions.

There are also differences in how experts believe the conditions may arise, and the ways to treat them.

Both disorders still face stigma from the public, due to being poorly understood, or portrayed badly in films, books, and TV.

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The nuance of mental health disorders means that lines between different conditions can be blurred — and in the case of schizophrenia and dissociative identity disorder (also known as multiple personality disorder) they can often be mixed up.

According to Dr Robert T Muller, a professor of psychology and specialist in trauma therapy from York University in Toronto, for those who haven't worked with people with schizophrenia or DID, certain similarities can make them easy to confuse.

"I think that the thing that is so compelling to people is the lack of reality, the sense of unreality, that both disorders have, and that's what makes it confusing," Muller told Business Insider. "With both of the disorders, there can be a sense of the individual being out of touch with reality."

The symptoms are very different.

Research from mental health charity Rethink Mental Illness found that 50% of people still believe having schizophrenia means you have a "split" personality, when in fact this isn't true.

When they are experiencing symptoms, people with schizophrenia may hallucinate, or have what is known as a thought disorder.

Muller explained that this means at the times when they are psychotic, their thinking is nonsensical.

"It is affected by their past, so it is not purely nonsensical, and it does often relate to something personal," Muller said.

Hearing is the most common hallucination, but there may be visual hallucinations, he said.

"A thought disorder is the difficulty to be able to think clearly," he said. "There may be delusions, where they believe that something is a truth that is not a truth. Being under a false impression that feels utterly and absolutely true — it is reality in their subjective experience."

People with dissociative identity disorder also experience an altered sense of reality

Instead of imagining external voices or visual hallucinations, when a person has DID, one alter checks out and another appears in their place.

While schizophrenics are likely to experience confusion and disorder, someone with DID can be incredibly organised, provided they are in the right personality at the time.

This phenomenon is very much on a sliding scale, with some people experiencing clear multiple personalities with their own functions and characteristics, and others effectively blanking out for a period of time.

With full-blown multiple personalities, they are there to serve different functions. Some are there for the day to day things, like going to school or getting to work. Others may be aggressive, or sexual, or shy. It's also common for different personalities to have different memories that others cannot recall.

For those who have DID in a much more diffuse sense, they have more permeability between their different states of consciousness. They may dissociate from a situation after being triggered, and then "wake up" several hours later, in a completely different place, after having finished an activity, like going to the shops.

This is why it is referred to as dissociative identity disorder in the Diagnostic and Statistical Manual of Mental Disorders (or the DSM-IV), as dissociating from the outside world is what connects people with the disorder together.

"The mind has developed these semi permeable walls, to wall off functions in memories, and it's incredibly unusual and fascinating," Muller said.

"When you're working with someone with DID, if you have only seen them in one personality, you will be utterly and completely shocked when you see the person function in a different personality... It's as if the person has gotten possessed by somebody else."

This is not actually the case — it's that their own internal personality organisation is different depending on different functions that they have in their life.

The causes aren't crystal clear for either disorder.

People develop the conditions at different stages in life. With schizophrenia, someone will have a break in their early 20s if they are a man, and in their mid to late 20s if they are a woman. With DID, it tends to be a much more gradual thing that happens from childhood, before the age of about 7.

Having a troubled past puts people at a higher risk for developing schizophrenia in their lifetime, but this connection is not well understood yet.

Over the years, there has been research suggesting schizophrenia is biological, or genetic, and thus is inherited. Muller said that during his undergraduate degree in the 1980s he was taught something called the dopamine hypothesis that backs this up, but in the years since, there has been insufficient data on this line of thinking.

Other studies have shown there is an increased risk of developing schizophrenia if you are an identical twin and they have the disorder, suggesting a genetic element. However, as Muller pointed out, if your identical twin has anything — like a penchant for spicy food — you are more likely to have that too, and this could be down to any number of different factors of nature and nurture.

Muller said every decade or so there is a new theory that is taught to psychiatric students until the next one comes along, such as the idea that schizophrenia is related to brain ventricles. However, it's still very unclear of what the causes really are.

People with DID have been through terrible psychological trauma

Muller said in almost every case, the patient has been through severe childhood trauma.

Several studies have shown the connection with childhood trauma and dissociation, including the work of Dr Bethany Brand, who looked into police records and found that people with DID had all routinely had severe violence or abuse in their childhood.

"These individuals almost always have severe physical, sexual, or psychological abuse from the caregiver," said Muller. "In fact, it's almost impossible to find a case of someone with DID who hasn't had that."

The individual has had a profound violation of trust or betrayal, he said, "a father or mother who has raped them, or sold them into prostitution at a young age, or another of the horrific things that happen to people."

The only way to cope with the traumatic experience is to shut off from the outside world. The individual goes into an altered state of consciousness as a way of coping — a bit like an immune response. The brain knows something is incredibly difficult to deal with and shuts off its awareness of the situation as a way of protecting itself.

There are different ways of helping people with each condition.

The film "Split" portrayed dissociative identity disorder in a less than favourable way. Universal Pictures

In Norway and Finland, schizophrenia is treated mostly by getting a lot of fresh air, exercise, and living in a community of people who accept your psychotic symptoms. Treatment programs that are outdoors and community based have been found to be a lot more effective than sending people to hospitals.

Social work can be very helpful for people with schizophrenia, because they often end up with substance abuse problems.

"Many homeless people are schizophrenics with nowhere to go," Muller said. "They're also much more likely to be imprisoned. The work often tends to be around helping them with day to day tasks, with medication and social work, helping them with access to some predictable job. You want to help people before they descend into ongoing psychosis."

There are drugs people with schizophrenia can take to reduce their psychotic symptoms when they occur. However, just like the research, these drugs have changed over time. They also don't work for everyone.

For those with DID, medication rarely helps at all

Muller said drugs "can help a little bit," with DID, but certainly do not help a lot.

"Many drugs have been tried, but nothing really seems to help that much drug-wise," he said. "Some of the drugs can numb the pain a little bit, so you get some people with DID on anti depressants, like Prozac. It can take some of the edge off, but it certainly doesn't cure the altered states of consciousness, or dissociating."

Whatever level of DID a patient has, drugs don't make it go away, or even change it in any way. Muller says it's the psychotherapy which can really help people.

He said [people] need therapists who understand trauma to help them deal with the memories of the past without getting badly triggered by them. He mentions and explains some of the concepts of trauma in his book "Trauma and the Avoidant Client."

DID is on the same spectrum as post traumatic stress disorder (PTSD), and so a big part of the therapy is digging into the past to find out where the trauma was, to face it, and to learn what it is in day to day life that might bring it back and make the patient fearful.

Nothing necessarily bad has to be happening to someone with DID to trigger dissociation either. It might be the way a room is lit, a topic brought up in a book or a film, or the sight of a particular item of clothing. It's just that something about the situation is similar to the one where they were incredibly scared, and their brain starts protecting them again.

People with schizophrenia and DID can live normal lives — but the stigma is the same.

A few months ago, Business Insider interviewed a few people who live with DID. The main point every interviewee wanted readers to know was that people with the condition aren't monsters, as they are sometimes portrayed to be in the media.

People with schizophrenia often experience stigma about their condition, too. A survey by Rethink Mental Illness found that 26% of people believe that schizophrenia makes you violent, and 23% think that someone with schizophrenia needs to be monitored by professionals at all times — both of which are incorrect.

"We've come a long way with mental health stigma, but schizophrenia remains behind many other conditions in terms of public understanding," said Brian Dow, the director of external affairs at Rethink Mental Illness.

"Many of us are still dramatically misinformed about the condition. The symptoms of schizophrenia don't fit neatly into a box, everyone will experience it differently. However, we can all play a role in rethinking schizophrenia, and helping to change attitudes, by learning to separate the myths from the facts."

With DID, Muller said people are often skeptical over its very existence, because on paper, it seems farfetched that someone can have multiple personalities.

"It's one of those conditions that people find spooky, and distressing to talk about, so they don't think it is a real thing, and [that] people just make it up," Muller said.

He added that people used to think this way about PTSD. Before there was a name and an official diagnosis, PTSD was known as shellshock, and people were just expected to snap out of it. In reality, PTSD is a response to overwhelming true events that occurred, and amidst a flashback, the person isn't really there anymore, just like when someone dissociates.

"You cannot have a conversation with a veteran who is in the middle of a flashback, and the flashback can last a while," Muller said. "They are right back there. They are on the battlefield as far as they are concerned."

Of course, not all flashbacks are that gripping, but it shows how the brain can enter a different state of consciousness, and suddenly it doesn't sound like the stuff of sci-fi anymore.

"[PTSD] is not something we doubt the truth of, so why do we doubt the truth or someone having been raped repeatedly by a father at the age of seven also having this kind of PTSD?" Muller said. "We give it a different name, but in all honestly, if you can have your mind so affected by a young man going into war, you'd also think a young impressionable child would react just as severely. It's not a big stretch."

Ultimately, it comes down to public awareness of both conditions to get people to understand them better, and realise that they aren't anything to fear. Having an altered state of consciousness doesn't mean you're suddenly a character in a horror film — like some books, TV shows, and films such as "Split" have unhelpfully suggested.

It also doesn't mean you're making things up. Afterall, sleep is an altered state of consciousness, too — it's just one that's normal and healthy. And nobody is queueing up to doubt the existence of sleep.