In 2006, a then 38-year-old woman in Spain had an extremely unpleasant sexual experience. After intercourse with her husband, her face became swollen and turned deep red. She also developed severe breathing problems. Her symptoms, which suggested an allergic reaction, began immediately after her husband’s ejaculation. The problem hadn’t occurred the previous times the two had used condoms. Because the woman wanted to become pregnant, the couple decided not to use contraception this time.

A few hours later, the victim sought medical help in the hospital. The doctors quickly found the cause of her symptoms. Using a skin prick test, they found that she was allergic to her husband’s semen. This is very rare – there are only around 100 such case reports in the scientific literature, and in none of them did the sexual act directly lead to the death of those affected. But that doesn’t mean that every allergic reaction during sex has a mild outcome.

This is shown by a report from Canada published in 2021, which describes how a young man lost his life as a result of fellatio. He met his newest partner on a dating app and they soon met for a date. What they didn’t know was that the first had a severe peanut allergy and the second had eaten peanut butter shortly before the date. While the second man performed oral sex on the allergy sufferer, he developed breathing problems. As an asthmatic, he had a bronchodilator with him, which he used immediately. However, a little later he collapsed and lost consciousness. An emergency team gave him artificial respiration and resuscitated him after his heart stopped. However, he died the next day as a result of the incident.

It was already known that passionate kisses can be dangerous for people with peanut allergies. It has been proven that symptoms occur up to six hours after a partner has a nutty snack. One study documented severe allergy symptoms two hours after a meal – even though the person had thoroughly brushed their teeth and rinsed their mouth in between. In the case from Canada, the two men had not kissed at all during their entire meeting. Just the contact of one person’s peanut-contaminated mouth with the other’s glans was enough to trigger the fatal reaction.

Allergens can also accumulate in ejaculate, as a case documented in Spain in 2019 shows. A woman who was 31 at the time was hospitalized after developing hives all over her body. She also vomited several times and complained of shortness of breath. Shortly before, she had had unprotected oral and vaginal intercourse. She had never reacted in this way to semen in the past; the only antibiotics she could not tolerate were penicillin antibiotics. However, her partner was taking one because of an infection. Because the doctors could not detect any other allergies, they concluded that traces of the active ingredient had gotten into the semen and caused the symptoms. The patient was given medication and recovered completely within a week.

All of these examples show that the exchange of bodily fluids poses more dangers for some of us than for others. People with severe food or drug allergies must therefore ensure that allergens do not enter their own body indirectly through their partner when making love. A condom can prevent this – and therefore not only protects against sexually transmitted infectious diseases, but also against potentially life-threatening immune reactions.

Incidentally, the medical team was able to fulfill the patient’s wish to have children despite her allergy to semen. To do this, they purified their partner’s ejaculate and isolated his sperm. They used these to successfully perform artificial insemination on the woman, which resulted in the birth of a healthy baby. However, the case report does not reveal whether the child inherited his mother’s allergy.

The original for this article “Sex, allergic shock, death: How this rare case can happen” comes from