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For a whole year, a 40 year-old man got headaches every time he would watch porn video online iStock

Taiwanese scientists were initially baffled by the case of a 40-year-old man who would only get headaches - or cephalalgia - while watching porn on the Internet.

Neurologists and sexologists from the Kaohsiung Chang Gung Memorial Hospital, in Taiwan, published their findings on the strange case study in the 164th volume of Clinical Neurology and Neurosurgery.

The man complained he suffered from throbbing headaches, with acute pain in his neck, vertex and bilateral temples.

Each headache would be preceded by the same symptoms: 10 minutes after starting a video, the man would experience flushes, his heart would pound in his chest, his breathing would quicken, his throat would turn dry and his penis would sometimes - but not all the time - harden.The headache would gradually get stronger and more painful. The pain would only stop when he switched off the porn.

Although it is not rare for people to experience headaches when they are sexually aroused, it is the very specific nature of what caused or didn't cause headaches that was of scientific interest.

Other sexual or non sexual activities would not trigger headaches, including watching normal movies or pictures, thinking of erotic films, masturbating and having sexual intercourse with his partner.

Further examination showed the patient's headaches were triggered mainly by graphic scenes depicting orgies with a number of close-up shots. He also experienced more pain when the actresses were young. However, men-on-men scenes didn't trigger headaches, which suggests the levels of pain would depend on the level of his sexual excitment.

Researchers reported the man didn't suffer from chronic migraines, hadn't undergone any cranial trauma, didn't take meds and didn't do drugs. All his blood tests came back clear. Cerebral exams, including a MRI, and a electroencephalography - EEG - were normal.

Sexual arousal and blood flow

When the routine exams didn't give them answers, the researchers decided to try something new, namely, a transcranial color doppler - a kind of ultrasonography that measures the velocity of blood flow through the brain's blood vessels by measuring the echos of ultrasound waves moving through the cranium.

The man was submitted to the exam while watching a pornographic video of his choice. It showed that his blood flow was faster in the left side of his face than the right side, causing the pain. According to the lead researchers, Drs Hsin-Ling Yin and Wei-Hsi Chen, it means the patient's sexual arousal is responsible for a cerebrovascular dysfunction.

"The visual perception of an erotic signal by the brain leads to sexual arousal," Dr Hsin-Lind and Wei-Shi told Le Monde. "The brain's blood flow [...] varies during a sexual response. We think that someone who gets headaches because of porn reacts in an abnormal way to a visual sexual stimulus."

They add that other factors could lead to vasomotor dysfunctions include anxiety and stress, feelings of shame and guilt and other negative emotions that could depend on how religious the person is.

The patient's headache was successfully treated by taking 25 to 50mg of indomethacin - a non steroidal anti inflammatory drug - 15 minutes before watching X-rated content.

The patient had been happily married for five years when the headaches occurred, and a psychological assessment revealed he had no psychological disorders or sex addiction. In other world, he was a normal guy with a normal sex-drive.

According to Hsin-Ling and Wei-Hsi's research, it is difficult to measure how common "pornography headaches" actually are as " pain-killer overuse may mask the actual incidence in real world." However, chances are they occur more often than we think.