Take a few moments to have a little think about sex. Ok, did you sneeze? No? Well, you are one of the lucky ones, as there are people out there with "sexually induced sneezing", a condition characterized by sneezing – sometimes uncontrollably – while thinking about or engaging in sexual activity. 

Another related condition called "Honeymooner's nose" sees people get nasal congestion when they are aroused or actively engaged in sex.

The conditions have been noticed and speculated on for a surprisingly long time, though they were not studied systematically until relatively recently. In an 1898 paper, one doctor notes that cases had been recorded from the 16th century of a man sneezing upon seeing a "pretty girl", other cases of "sneezing during coitus", and some patients who bleed from the nose during sex or masturbation.

"Quite a number of such cases have come under my personal observation in persons in robust health and whose nasal organs were apparently free from disease," the doctor wrote of sexual sneezing. "The reflex may occur before (from erotic thoughts), during, or after the consummation of the act."

The 1898 paper makes several links between the nose and the genitals. Curiously, the case study makes reference to the size of the nose being linked to the size of the penis, aka the "big nose, big hose" hypothesis.

"The nose, for example, that was large and firm was looked upon as an index of a penis acceptable to women, and hence it was that the licentious Emperor Heliogabalus only admitted those who were nasuti, i.e., who possessed a certain comeliness of that feature, to the companionship of his lustful practices," the author wrote.

"Johanna, Queen of Naples, a woman of insatiable lust, seems also to have selected, as her male companions, men with large noses, with a similar end in view."

They also write of "the case of a woman who anticipated a large penis from the size of her lover's nose, and, whose hopes being frustrated, is said to have exclaimed, ' Oh, nose ! how thou hast deceived me!'."

One hundred years later, science hadn't advanced much more on the topic of sexual sneezing, other than doctors occasionally noting anecdotally that a patient sneezed whenever they came. Then in 2008, a team of doctors published in the Journal of the Royal Society of Medicine took a more systematic look at the phenomenon.

The doctors searched through Internet chat rooms using Google, in an attempt to see how widespread the problem was. They found that 17 posters (both male and female) reported sneezing upon thinking about sex, with three others reporting sneezing after they orgasm. Replying to the threads, others said that they had the same, strange condition.

"In the reports it appears the sneezing occurs immediately upon sexual ideation, or very soon after orgasm," the team wrote, adding that the condition may be underreported due to embarrassment.

"It also seems that the two phenomena do not occur in the same person, i.e. that these are two distinct entities: sneezing with sexual ideation or sneezing with orgasm."

The doctors wrote of a number of possible mechanisms for how sneezes are caused by sex, or even thinking about sex. Included in this was the possibility that nitric oxide – released to cause tumescence in the genitals – enters the bloodstream and "causes engorgement and irritation of the nasal mucosa too". However, they discount this and other explanations as the sneeze reflex appears to be more immediate than this.

In the end they put the phenomenon down to the misfiring of signals in the autonomic nervous system – though they admit that it is difficult to explain given the lack of experimental data, and the self-reported nature of the condition.

"It certainly seems odd, but I think this reflex demonstrates evolutionary relics in the wiring of a part of the nervous system called the autonomic nervous system," Dr Bhutta, a specialist in ear, nose and throat medicine at Oxford's John Radcliffe Hospital told the BBC at the time.

"This is the part beyond our control, and which controls things like our heart rate and the amount of light let in by our pupils. Sometimes the signals in this system get crossed, and I think this may be why some people sneeze when they think about sex."

The team believes that there is likely a genetic cause for the condition, which causes sex to be a lot more mucusy than is ideal.