Doctors say an uncommon sexually transmitted disease, Mycoplasma genitalium (MG), which often has no symptoms may pose a great health risk if people aren't more cautious.
Experts say a lack of test kits means it is regularly confused with chlamydia and treated with incorrect doses of antibiotics - building up unsafe antibiotic resistance which could see it soon become untreatable.
Bad cases can cause painful inflammation for men, but can be more serious for women - potentially causing womb scarring that leave them infertile.
The British Association of Sexual Health and HIV says that the infection is often mistaken for other sexually transmitted infections with similar symptoms, meaning that patients are given...
The news comes after health officials a year ago warned that millions of young people are shunning protection because risky sex has become acceptable once again, three decades after the Aids epidemic made condom use essential.More news: Djokovic back in the Wimbledon semis for eighth time
MG can be missed - and if it is not treated correctly, it can develop resistance to antibiotics. In Europe, that number dips slightly to 1% to 2% of the population, the guidelines state.
Although tests for MG have been developed they are not now available at all clinics.
Eradication rates of MG following treatment with one family of antibiotics, called macrolides, are decreasing globally.
Paddy Horner, of BASHH, said last night: "MG has the potential to become a superbug within a decade, resistant to standard antibiotics".
Dr Peter Greenhouse, a sexual consultant in Bristol and BASHH member, urged people to take precautions.More news: Selena Gomez Doesn't Think Justin Bieber & Hailey Baldwin Will Actually Get Married
Almost half of 16 to 24-year-olds admit they have had sex with a new partner without using a condom, a Public Health England report said in December.
"We are asking the government directly to make this funding available to prevent a public health emergency waiting to happen and which is already spiralling out of control".
The most recent figures from Public Health England show that diagnoses of syphilis are at their highest level for almost 70 years, with 7,137 cases in 2017, a 20 per cent rise on the previous year, and more than twice that recorded in 2012.
"Everyone can protect themselves from STIs by consistently and correctly using condoms with new and casual partners".More news: NASA Spacecraft Picked Up Weird Plasma 'Sounds' As It Plunged Into Saturn