Use of the internet may increase the risk of self-harm and suicide among socially isolated and vulnerable teenagers, a major new review has concluded.

Researchers at Oxford University in the UK analysed 14 international studies in an attempt to ascertain whether the internet helped or hindered young people in a vulnerable state.

Some of the studies found that internet discussion forums can provide a support network for young people who feel socially isolated, helping them to cope better in certain situations.

However, other studies found that the internet can lead to more risky behaviours. For example, some vulnerable people who went online to find out more information about self-harm and suicide ended up seeing violent images and subsequently went on to act out what they had seen.

The review, which is thought to be the biggest of its kind, also found that internet use appeared to be linked to more violent methods of self-harm.

Overall, vulnerable teenagers with a moderate or severe addiction to the internet appeared to be at an increased risk of self-harming, experiencing suicidal thoughts and depression.

In one of the studies analysed, almost 60% of teenagers admitted to researching suicide on the internet. Among those who had carried out particularly violent acts of self-harm, eight in 10 said they had gone onto the internet to learn more about this practice. Among those who cut themselves, three in four researched it online beforehand.

The review found that when it came to using discussion forums, anonymity was important. Most people went online in the hope that others would empathise with them. They were not as interested in discovering ways of reducing self-harm behaviour.

In one study, some young people were going online to swop tips on how to conceal the problem.

In relation to making people feel better, the results were contradictory. One study found that discussion forums did not make the teenagers feel any better. In fact, they became more distressed. However another study found that a few months into their internet use, the teenagers were less distressed.

Some said they found the forums encouraging, as people congratulated them if they managed not to self-harm, while others were even encouraged to go to their GP about the problem.

However, the review found that while some people felt supported by these forums, the amount of self-harming did not appear to decrease.

Meanwhile, the review also pointed to the dangers of cyber-bullying, which appeared to make vulnerable teenagers more likely to self-harm. The most common form of cyber-bullying was via email, followed by instant messaging.

Discussing the findings, the review's senior author, Prof Paul Montgomery of the University of Oxford, emphasised that the findings do not show that ‘all young people who go on the internet increase their risk of suicide or self-harm'.

"We are talking about vulnerable young people who are going online specifically to find out more about harming themselves or because they are considering suicide already. The question is whether the online content triggers a response so that they self-harm or take their own lives and we have found that there is a link," he explained.

Lead author, Kate Daine, also noted that there are no known online interventions that specifically target vulnerable young people at risk of self-harm or suicide.

"Yet we find that adolescents who self-harm are very frequent users of the internet. While social media might be useful for supporting vulnerable adolescents, we also find that the internet is doing more harm than good in some cases. We need to know more about how we can use social media as a channel to help young people in distress," she commented.

Details of these findings are published in the journal, PLOS ONE.