We know that infections can be transmitted between two people through the exchange of bodily fluids that occurs during sexual intercourse, but what about allergies? Can you trigger an allergic reaction in a partner during sex?
It would seem that the answer is 'probably.' The most widely reported case of an allergic reaction which occurred after intercourse is that of a woman from Surrey who developed symptoms consistent with an allergic reaction after having sex with her boyfriend who had eaten Brazil nuts a few hours earlier. The case was reported by the Daily Mail in 2011, although it was documented in a scientific paper four years previously, in 2007.
The paper records that 'The patient’s partner was aware of the patient’s very significant nut allergy and had bathed, brushed his teeth and cleaned his nails immediately before intercourse as he had consumed mixed nuts roughly two to three hours earlier.'
The patient's symptoms included significant itching and swelling of her vagina and vulva, feeling faint, and a shortness of breath. Her condition improved after taking medication.
In order to test the hypothesis that it was the boyfriend's semen which had been the agent for the transfer of traces of Brazil nut, doctors at the Department of Immunology at St Helier Hospital in Carshalton, Surrey performed standard allergy skin tests using semen before and after Brazil nut consumption. They report that the tests 'confirmed the presence of an allergenic nut protein.'
The paper also claims that while there are known cases of allergies being transmitted through touching or kissing, 'To our knowledge this is the first case of a severe food allergic reaction transferred by normal vaginal intercourse.'
The Daily Mail speculated in its report that the reason an allergy triggered through intercourse is specific to Brazil nuts is that 'It appears that Brazil nut proteins resist digestion, which is why they generally end up in the immune system, triggering immune reactions.'
If you think that sounds far-fetched, you'd be right. Science blogger Kevin Bonham was sceptical too and after a little digging turned up a report from 1986 which referenced a third paper from 1978 in which, according to Bonham 'a woman who has an allergy to walnuts has an allergic reaction to her husband’s semen after he’s eaten walnuts, but not before.'
In the case documented in the 1986 paper, the patient was not only allergic to several foods, but also to her husband's sweat, hair, and semen, her sons' sweat, and semen from a pool of anonymous donors. Allergy testing is an uncomfortable process at the best of times, but there can be few tests more uncomfortable than having semen from anonymous donors inserted under your skin.
Of those who donated potential allergens. only one of her sons was known to eat the foods to which she was allergic. Doctors concluded that while the woman was allergic to certain foods, her allergies to sweat, hair and semen where unrelated to the dietary allergies. Further testing was prevented because, according to the paper, the woman 'solved her problem, at least temporarily, by leaving her husband! She did not wish to return for further testing.'
The only other possible evidence for the triggering of dietary allergies by the transfer of semen is anecdotal. One commenter on another post by Bonham reported 'I’ve got an allergy to a certain fruit, my (also female) partner has an allergy to a different fruit in the same group. We have to avoid eating the fruit that the other is allergic to, as even if we avoid oral contact, the mutual allergies seem to cause reactions after contact with each others’ secretions.'
It seems likely, given what evidence exists, that dietary allergies can be triggered through the exchange of fluids during sex when one partner has eaten something to which the other is allergic. It also appears to be rare, given the lack of documented cases.
More common is an allergy to semen itself. While there are few reported cases of Seminal Plasma Protein Allergy (SPPA), that's thought to be due to under-recognition and under-reporting of the condition. In one of the few studies to be carried out, 1000 women were surveyed and 12% were believed to have 'probable' SPPA, while another 25% had possible SSPA. Thankfully those who do have the allergy, it's easily prevented by using a condom.
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