A woman whose vagina burned after sex was told her partner's semen contained traces of peanuts, which was making her allergy flare up

• A woman with a peanut allergy had an itchy vagina after condom-free sex with her partner.
• Doctors couldn't find an infection, so they told her partner to stop eating peanuts.

Doctors in Delaware discovered a 28-year-old woman's peanut allergy made her vagina itchy and inflamed after her partner ejaculated inside of her.

The two doctors who treated the woman explained how they figured out that her partner had traces of peanuts in his semen, and that she was having a rare allergic reaction, in a November 10 case study in the journal Annals of Allergy, Asthma, & Immunology.

While taking the woman's medical history, the doctors learned she was allergic to peanuts and tree nuts. Thinking her adverse reaction could be related to her partner's semen, the doctors said he should remove peanuts from his diet.

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."

One woman who was allergic to the antibiotic penicillin went into anaphylactic shock after she swallowed her partner's semen, which contained traces of it, according to a case study in BMJ Case Reports. In April, Australian OnlyFans creator Lucy Banks told the Daily Mail Australia she had an allergic reaction after sex because her partner ate peanuts the day before.

The woman in the case study, who was unnamed, told the doctors she and her partner were trying to have a baby. She noticed that if her partner didn't wear a condom and ejaculated inside of her, her vagina would itch, burn, and release an unusual discharge. She said that if he wore a condom or didn't ejaculate, her vagina felt fine.

The doctors diagnosed her with vaginitis, a condition where the vagina becomes inflamed, with signs including vaginal itching, bleeding, abnormal discharge, and pain during sex or urination, according to the Mayo Clinic. It's typically the result of an infection due to things like yeast, bacteria, or trichomoniasis, an STD caused by parasites.

But the doctors didn't find signs of any infection in the woman, so they told her partner to stop eating peanuts.

When he did that and they had unprotected sex, the woman didn't have a bad reaction, leading the doctors to believe small amounts of allergens in his semen caused the vaginitis.