The woman also had trouble breathing, and when doctors investigated, they discovered she had an allergy to the antibiotic penicillin. Her partner had traces of a similar antibiotic, amoxicillin, in his semen, according to BMJ Case Reports.
He had been taking amoxicillin to treat an ear infection.
Allergens transferred through sex have barely been studied, and this case is one of the first that demonstrates the phenomenon.
Another study, published in 2007 in The Journal of Investigational Allergology and Clinical Immunology, involved a woman who also had an allergic reaction after swallowing her partner's semen. She was allergic to Brazil nuts, and doctors found traces of them in his semen after he ate some earlier that day.
Though rare, trace amounts of allergens can show up in a person's semen if they eat a certain food regularly, according to the doctors. Studies on the phenomenon are non-existent since it's uncommon, but there have been other anecdotal reports of what the woman's doctors called "allergic vaginitis."