The survey, published on Friday, concluded that Snapchat, Facebook and Twitter are also harmful. Among the five only YouTube was judged to have a positive impact.
The four platforms have a negative effect because they can exacerbate childrens and young peoples body image worries, and worsen bullying, sleep problems and feelings of anxiety, depression and loneliness, the participants said.
The findings follow growing concern among politicians, health bodies, doctors, charities and parents about young people suffering harm as a result of sexting, cyberbullying and social media reinforcing feelings of self-loathing and even the risk of them committing suicide.
Its interesting to see Instagram and Snapchat ranking as the worst for mental health and wellbeing. Both platforms are very image-focused and it appears that they may be driving feelings of inadequacy and anxiety in young people, said Shirley Cramer, chief executive of the Royal Society for Public Health, which undertook the survey with the Young Health Movement.
She demanded tough measures to make social media less of a wild west when it comes to young peoples mental health and wellbeing. Social media firms should bring in a pop-up image to warn young people that they have been using it a lot, while Instagram and similar platforms should alert users when photographs of people have been digitally manipulated, Cramer said.
The 1,479 young people surveyed were asked to rate the impact of the five forms of social media on 14 different criteria of health and wellbeing, including their effect on sleep, anxiety, depression, loneliness, self-identity, bullying, body image and the fear of missing out.
Instagram emerged with the most negative score. It rated badly for seven of the 14 measures, particularly its impact on sleep, body image and fear of missing out and also for bullying and feelings of anxiety, depression and loneliness. However, young people cited its upsides too, including self-expression, self-identity and emotional support.
YouTube scored very badly for its impact on sleep but positively in nine of the 14 categories, notably awareness and understanding of other peoples health experience, self-expression, loneliness, depression and emotional support.
However, the leader of the UKs psychiatrists said the findings were too simplistic and unfairly blamed social media for the complex reasons why the mental health of so many young people is suffering.
Prof Sir Simon Wessely, president of the Royal College of Psychiatrists, said: I am sure that social media plays a role in unhappiness, but it has as many benefits as it does negatives.. We need to teach children how to cope with all aspects of social media good and bad to prepare them for an increasingly digitised world. There is real danger in blaming the medium for the message.
Tom Madders, its director of campaigns and communications, said: Prompting young people about heavy usage and signposting to support they may need, on a platform that they identify with, could help many young people.
However, he also urged caution in how content accessed by young people on social media is perceived. Its also important to recognise that simply protecting young people from particular content types can never be the whole solution. We need to support young people so they understand the risks of how they behave online, and are empowered to make sense of and know how to respond to harmful content that slips through filters.
Parents and mental health experts fear that platforms such as Instagram can make young users feel worried and inadequate by facilitating hostile comments about their appearance or reminding them that they have not been invited to, for example, a party many of their peers are attending.
May, who has made childrens mental health one of her priorities, highlighted social medias damaging effects in her shared society speech in January, saying: We know that the use of social media brings additional concerns and challenges. In 2014, just over one in 10 young people said that they had experienced cyberbullying by phone or over the internet.
In February, Jeremy Hunt, the health secretary, warned social media and technology firms that they could face sanctions, including through legislation, unless they did more to tackle sexting, cyberbullying and the trolling of young users.