Refugees have increased risk of psychotic disorders as compared to native-born and other people who have migrated for other reasons apart from fleeing war, according to a new Swedish study published in BMJ medical journal.

Fleeing persecution, wars, bloodshed, and natural disasters can leave scars in a person, which makes him or her vulnerable to psychosis such as schizophrenia and other Post-Traumatic Stress Disorders (PTSD).

Although previous studies have suggested that refugees are prone to developing post-traumatic disorders, the recent survey focused on the risk of schizophrenia and other psychoses.

The research was conducted by scientists at Karolinska Institute in Sweden and University College London, and is based on cohort study of 1.3 million teens in the Nordic country, who were followed for 13 years.

The researchers tracked the immigration and health records of people who were born after 1983, and checked their mental health status from 14 years after and onwards till 2011.

The study followed Swedish citizens with two native parents, and other migrants from all over the world including from sub-Saharan Africa, Eastern Europe and Russia, North Africa, and Middle-East.

"The dramatically increased risk among refugees shows that life events are a significant risk factor for schizophrenia and other psychoses," Anna-Clara Hollander of Sweden's Karolinska Institute said in a UCL press release.

The research found that refugees were three times more likely to develop schizophrenia and other psychotic diseases than native-born.

For every 10,000 native born citizens, four cases of psychoses was found; among non-refugees who migrated for any other reason such as economic factors, eight; and among the refugees, 12.

Schizophrenia symptoms include paranoia, delusions, and hallucinations, and its onset is usually observed in teenagers transitioning to adulthood.

Both genetic and social circumstances such as witnessing trauma, persecution, family problems, etc. are thought to contribute to the probability of disorder.

"These differences cannot be explained by other, important alternative explanations like differences in age, sex, income or urban residency," said study co-author James Kirkbride of the University College London.

"We know that refugees are a vulnerable group, facing many social, economic, physical and mental health challenges in their lives," Kirkbride noted.