Men can develop an allergy to their own orgasms which causes them to suffer flu-like symptoms whenever they ejaculate, a study has found.
Scientists identified at least 60 cases in which men suffered with fever, cough, sneezing and muscle weakness - a condition known as post-orgasmic illness syndrome.
Other men also experienced problems with their speech, concentration and memory, with these issues lasting for a few days or as long as a week.
Andrew Shanholtzer, from the Oakland University William Beaumont School of Medicine, said the condition is often "underdiagnosed" as it is not well-known among the medical community.
The researcher, who is a co-author of the study, explained: "Many health providers do not know about it, let alone the public.
"It is more than likely that it is underdiagnosed, with many sufferers out there."
Mr Shanholtzer explained the issue can start when an injury or infection to the testicles leads to a small amount of sperm leaking into the bloodstream, which triggers a response from the body.
He added that immune cells in the body are trained to attack any foreign substance found, but special cells - known as Sertoli cells - keep the sperm isolated and protected.
However, when the Sertoli cells are damaged, the sperm is exposed to the immune system which attacks it as if it was a virus or a bacterium.
This, in turn, causes men to suffer flu-like symptoms.
The team of scientists researched the condition after a 27-year-old man started developing a cough, a runny nose and sneezing, as well as a rash on his arm whenever he had an orgasm.
The doctors - who wrote about the patient in the peer-reviewed medical journal Urology Case Reports - said the man avoided any sexual activity or romantic relationships due to the nature of his symptoms, and doctors did not find any issues with his testicles, semen or hormones.
Researchers found that antibiotics did not help the man, but fexofenadine - an antihistamine medicine that helps with the symptoms of allergies - eased his symptoms by 90 per cent.
Post-orgasmic illness syndrome (POIS) is a rare condition in which a person develops flu-like and allergy symptoms after orgasm, whether with a partner, through masturbation, or spontaneously during sleep, explains the Genetic and Rare Diseases Information Center.
The most common symptoms include fatigue, weakness, headache, fever, mood changes, memory or concentration problems, stuffy nose, sore throat and itching eyes.
Symptoms may develop within seconds, minutes or hours after orgasm, and usually last for two to seven days before going away on their own.
