People with sexually transmitted infections (STIs) are using Reddit to try and get diagnosed without having to see a doctor, scientists have warned.
A study found thousands of posts have been submitted to the social media site by people worried about their sexual health.
Many include graphic close-up photos of their genitals, while others give detailed accounts of their sexual history.
The forum studied in the research – r/STD – has more than 10,000 regular visitors and even has 'trusted contributors' who can comment on people's posts without showing any clear medical credentials.
Experts warn these forums may distract people from going to see a real doctor or lead to wrong or delayed diagnoses, putting their future partners at risk.
Experts say people are turning to the online community to help them diagnose concerns about their genitals, which might delay them going to an actual doctor
The r/STD community has more than 10,000 members and there have been more than 17,000 posts since it was formed in late 2010 – researchers found it is becoming more popular
A team of researchers led by the University of California, San Diego, analysed a total of 16,979 posts on the STD forum between 2010 and February 2019.
It has become substantially more popular over the past eight years, with the number of monthly posts rising from fewer than a dozen to up to 500.
The scientists found 58 per cent of all the posts were from people asking for a 'crowd-diagnosis'.
And almost a third (31 per cent) contained a photograph of the reported symptoms. Some 79 per cent of posts received a reply within a day of of being submitted.
Among post titles at the top of the page today were 'What is wrong with my penis?'; 'Is the dermatologist wrong?' and 'Is this herpes?'.
Many are accompanied by photographs claiming to be of the posters' genitals, with some showing obvious signs of sexually transmitted skin infections.
Writing in their paper the researchers, led by Dr John Ayers, said: 'Although crowd-diagnoses have the benefits of relative anonymity, rapid response, and multiple opinions, the underlying accuracy of crowd-diagnoses is unknown...
'Responders may be operating with limited information about the patient, and responders may lack medical training.
'Misdiagnosis could allow ongoing disease transmission, and others viewing a post may wrongly self-diagnose their own conditions.'
Experts at British sexual health charity the Terrence Higgins Trust said online advice was useful but not a substitute for real medical help.
And people should not choose to go online out of embarrassment, they added.
Some 58 per cent of all posts on the r/STD community were from people who wanted a 'crowd-diagnosis' from other users on the social media site, researchers said
While some users share photographs of their genitals, others go into detail about their sexual history and ask for advice from fellow users
Clinical director at the charity, Liz Porter, told MailOnline: 'The staff [at sexual health services] are all trained professionals who provide a