There's a warning not enough is being done to stop the spread of sexually transmitted infections (STIs) through oral sex.
Some of the UK's leading sexual health doctors fear people who change partners frequently may not be adequately protecting themselves.
The British Association for Sexual Health and HIV (BASHH) says it's causing the spread of STIs like genital herpes, chlamydia and drug-resistant gonorrhoea.
Most recent numbers show sharp rises in genital herpes, gonorrhoea and syphilis.
"We've only really just noticed that a lot of infections are passed on from oral sex," Dr Peter Greenhouse, who advises on UK government sexual health policy, told Newsbeat.
The majority of new STI cases are among under-25s and gay men.
People are passing on more infections through oral sex than previously thought, BASHH says.
"Very, very few people are using condoms for oral sex," says Dr Greenhouse.
Oral sex is now believed to be the main way people get genital herpes.
But is it unrealistic to expect people to use condoms and dental dams, which cover the vagina, for oral sex?
"If you're out there, in what we might politely describe the sexual market place, or the Tinder-place, there are two ways to go," says Dr Greenhouse.
"Get yourself down to the clinic to get yourself tested regularly or be meticulous about condom use, including for oral sex."
Dr Greenhouse says there's a reason the new advice is being issued now.
"We realise that oral sex is now the principal mode of transmission of drug-resistant gonorrhoea."
Clinical testing suggests antibiotics used to treat gonorrhoea don't penetrate the throat as well as the rest of your body.
"So you can have it cured in your genitals but still might have it in your throat," he explains.
"So you can pass it on."
Oral sex and under-25s
Newsbeat asked three students in Newcastle whether they take precautions for oral sex.
Sam, Adam and Daniel were happy to talk to us.
Adam says most people don't even think about oral sex and condoms.
"I haven't thought about it with oral sex [but] I know my friend has. But I don't change partners as much."
For Sam it's not something people associate with STIs.
"I wouldn't say so. People don't really think about that. I think that would be the last thing on your mind.
"When you're out in Newcastle you don't really think about an infection like that from someone's mouth."
Sam does think people under 25 are more likely to use condoms than older people, but only when it comes to genital sex.
"I think some people would get a condom out or whatever but not for oral sex."
Daniel thinks it's embarrassing when people ask to use a condom.
"When I got asked to have oral sex with a condom on, I was absolutely livid. It just doesn't feel the same."
If you're worried about STIs or want to know more about the symptoms you can read BBC Advice pages here.
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