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.
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.
Clinical director at the charity, Liz Porter, told MailOnline: 'The staff [at sexual health services] are all trained professionals who provide a non-judgmental service.
'I’ve worked in sexual health for years and I can assure you we’ve seen it all before.
'The internet has been brilliant for making health information more accessible... but for correctly diagnosing STIs the internet is no substitute for a trained professional who can give a proper diagnosis and proper treatment.
'Rates of some STIs are soaring – including syphilis and gonorrhoea – and successful treatment is vital for stopping the spread, which is why it’s important to get that diagnosis as quickly as possible.'
Reddit is a completely anonymous form of social media which allows people to – in most cases – post without anyone ever knowing their true identity.
They can even create one-off 'throwaway' accounts to make posts or comments which can't be linked back to their past activity.
In the r/STD forum, at least one commenter was flagged as a 'trusted contributor', although it was not clear whether they were a qualified medic.
The researchers who did the study were concerned that users second-guessing doctors' opinions might not get treated as quickly as they should be.
And delays to treatment could make them more likely to spread the infections to other people.
But they also acknowledged that forums like this could have doctors taking part to help people get more accurate help more quickly.
They added: 'Health care professionals could partner with social media outlets to promote the potential benefits of crowd-diagnosis while suppressing potential harms, for example by having trained professionals respond to posts to better diagnose and make referrals to health care centers.'
The research was published in the Journal of the American Medical Association (JAMA).
MailOnline has contacted Reddit for comment.
This article has been adapted from its original source.
© Associated Newspapers Ltd.