People who are mugged or randomly attacked in the street remain paranoid and distrustful of others for several months after, a new study has found.

UK researchers followed the progress of over 100 people who had attended hospital with minor injuries following some sort of physical assault. The participants were monitored for symptoms of paranoia and post-traumatic stress disorder (PTSD) for six months.

PTSD is an anxiety disorder that can occur after experiencing an intensely stressful event in which grave physical harm occurred or was threatened. It has been well documented in relation to military conflict, but it can also occur as a result of other scenarios, such as road traffic accidents or a violent attack.

While it is known that assault victims can suffer PTSD, this is the first study to look at how paranoia affects them.

It found that most mugging and assault victims were still paranoid and distrustful of others six months after the incident. In fact, four out of five victims said they were more afraid of other people than they wanted to be.

There were a number of issues that appeared to increase this level of mistrust. They included being attacked close to home and feeling unsupported by others after the attack.

The study also found that the fear the victim felt about their attacker often spread to other people. As a result, the victim was wary of many people around them, for example, two in three said they were afraid of all males following their attack.

One in 10 of the study participants was found to have high levels of paranoia in the months following the attack.

According to lead researcher, Prof Daniel Freeman, of the University of Oxford, it is ‘very understandable' that people are more wary after being attacked.

"Our mindset may become more like that of a bodyguard, vigilant for danger. When we are overly mistrustful, that is a form of paranoia. It may well be a normal temporary change in our thinking after being a victim of attack. The danger of such thoughts, however, is if we isolate ourselves, close off from others and spend our time thinking only of the worst. It is an under-recognised problem in the aftermath of an attack," he explained.

He noted that for many people, these fears will ease over time. However, the study identified ‘several key factors...that made the paranoid fears much more likely to remain'.

"If we are attacked in places or by people we know, that leads to greater mistrust than being attacked by a stranger or in unfamiliar places. The trust we had becomes broken. If during the assault we feel destroyed as a person or we become detached from ourselves, then mistrust typically stays for longer.

"Afterwards if we feel down on ourselves, ruminate and worry, and start to take excessive precautions, then fears will stay in mind," Prof Freeman explained.

On the other hand, having a good support system and getting good sleep appears to benefit people who have been attacked.

Prof Freeman explained that traditionally, paranoid thinking was thought to be rare in the aftermath of an attack and was more commonly associated with severe cases of PTSD.

"However fears about other people may well actually be typical. If you have been attacked, these sorts of thoughts are to be expected. And paranoid thoughts are much more likely to remain depending upon how we respond both during and after the attack.

"We plan to use this information to improve the latest generation of cognitive behaviour therapies for those seeking help," he said.

Details of these findings are published in the journal, Psychological Medicine.