Friday Weird Science: Nutty Semen

Aug 12 2011 Published by under Friday Weird Science

Sci will be honest: I hate Brazil nuts. I have no idea why anyone eats them, they always taste all sour and gritty and WEIRD. The taste just kind of lingers in your teeth. But what if it didn’t just linger in your teeth? What if it lingered in your…semen?

Ah, Sci, you say. You’re always all about the semen.

Bansal et al. “Dangerous Liason: Sexually transmitted allergic reaction to Brazil Nuts” Journal of Investigative Allergy and Clinical Immunology, 2007.


Semen allergy is actually more common than you might think. Many people can show allergy to some of the components of semen, which can make sex both seriously uncomfortable and really, really obvious. Not to mention problems if you’re trying to get pregnant! But that’s an allergy to semen itself. What about an allergen, an allergic reaction TRANSMITTED through the semen?

That’s what apparently happened here. 20 year old woman with a boyfriend. Woman had a really bad allergy specifically to Brazil nuts. While she gave them up after getting diagnosed, her boyfriend apparently had a real nut fetish and couldn’t stay away from the mixed. In an effort to protect her, he carefully bathed, brushed his teeth (there have actually been deaths in those with nut allergies when they get kissed after someone else eats nuts), and even cleaned out his fingernails before sex. All in vain. Immediately after sex she began to suffer itching and swelling of the vag, got short of breath, and felt faint. A little bit of antihistamine helped to solve the problem, but it was bad enough that she ended up going to the doctor.

When the doctors had ascertained that the boyfriend had been extremely careful and her symptoms were not simply due to REALLY bad sex (you never know…), they decided to test the semen. They brought the poor guy in and demanded two semen samples, one before, and one four hours after eating Brazil nuts (no word on whether his girlfriend was allowed to help him obtain the sample, my guess is he had to go it alone). They then took the samples, and performed a prick test on the girl, where they give a small prick with a needle covered in semen underneath the skin (sounds SO FUN!). This is a common way to test for particular allergies. Often they’ll do a whole slew at once over your arm or your upper back, pricking you with all sorts of things and having you wait a few hours or even a day to see if you react (Sci has had this done before, though not with semen. Would you believe I’m allergic to watermelon?). The net result of this is that you can end up with a pile of permanent marker bits and lumps all over your back. I don’t recommend getting it done in the summer.

Anyway, the poor girl got pricked with semen! And this is what they got.

On the left you can see the after effects of a normal semen prick, while on the right we have a semen prick following the guy eating four Brazil nuts (apparently they were controlling for his past consumption, when he had had 3-4). The lighting is…questionable and somewhat misleading, but it does indeed appear that she had an allergic reaction to the semen only after her boyfriend went for the nuts, though it doesn’t look like it’s as large as they say, this could be an effect of time.

One can only imagine what the girl thought when the doctors got all excited about this. The reason they got excited is that this may be the first time that an allergen has been documented to be sexually transmitted. Not just via contact with the skin or something, but in the SEMEN. The authors think there’s no other way for the allergy to have got in there, and indeed it was really localized to the vagina.

I’m mostly surprised by how FAST the Brazil nut proteins apparently got into the seminal fluid. I mean, 3-4 hours isn’t very long. While sperm itself turns over much more slowly, the idea of the proteins from the Brazil nuts getting into the seminal fluid is not unheard of. Unfortunately, the couple broke up soon afterward (given a choice, I guess he chose the Brazil nuts), and so unfortunately they couldn’t get him to donate anymore semen to the cause. If they’d had a chance, they probably would have tried to find which proteins from the nuts in particular made it into the semen, and how long they stayed there.

I have to say I’m a little surprised we haven’t heard of this before. Maybe in most long stable relationships, the partner of the person with the allergy is a little more likely to give up eating the allergen? Or maybe many potential transmissions have been missed due to condom use (no condom use in this case). Either way, it’ll be interesting to see if more of these cases turn up. And if you’re someone who has a severe food allergy, watch your partner’s semen. You never know! And it’s probably a plenty good excuse not to swallow!

Bansal AS, Chee R, Nagendran V, Warner A, & Hayman G (2007). Dangerous liaison: sexually transmitted allergic reaction to Brazil nuts. Journal of investigational allergology & clinical immunology : official organ of the International Association of Asthmology (INTERASMA) and Sociedad Latinoamericana de Alergia e Inmunologia, 17 (3), 189-91 PMID: 17583107

23 responses so far

  • Adrian Blake says:

    WARNING! this semen was made in an environment that contains nuts.

    Nailed it!

  • inez says:

    Haha, a semen sample after he went for the nuts. Freudian slip or pun intended? Funny nonetheless!
    There's a small, but important mistake tho: the ALLERGY is not sexually transmitted, but the REACTION. a sexually transmitted allergy would imply that she wasn't allergic to brazil nuts before but now, thanks to her boyfriend, she is. 🙂

    • scicurious says:

      No, actually I think even that is inaccurate. Not the REACTION was transmitted, because that would imply he was having one, too. It's the ALLERGEN that was transmitted. The substance itself.

      • inez says:

        But the title of the article is:
        "Dangerous liaison: sexually transmitted allergic REACTION to Brazil nuts"
        Anyway, with an STD, the D is transmitted. With and STA (A=allergy), the allergy would be transmitted. You're right about STAR (allergic reaction) being inaccurate. So, conclusion: it should be STA with A for Allergen?

  • seth says:

    NB. This side of the pond prick is slang for penis ; so she had a prick before the prick test .With the different reactions to the prick and prick test is it proof that size does matter ?

  • Tsu Dho Nimh says:

    "I have to say I’m a little surprised we haven’t heard of this before. Maybe in most long stable relationships, the partner of the person with the allergy is a little more likely to give up eating the allergen?"

    Or the allergic person avoids getting into sexual relationships with allergen consumers?

    I am allergic to tobacco - can't handle cured tobacco, tobacco leaves, smoke-covered objects, or any part of that plant without breaking out in hives wherever the allergen contacts me. I learned very early in my adult years that sex with tobacco smokers would have extremely uncomfortable consequences ... so I wouldn't even date them.

  • gerty-z says:

    this post is so full of win that i don't even know what to say. well done, once again 🙂

  • Ron says:

    I had those tests done on my fore arms. I ended up with 2 hockey puck shaped welts on my arms. Each test site reacted and then they all blended together. The doctor actually told me that I have problems with allergies and that I'm very allergic. Wow, if only I had gone to med school I would have been able to figure that out.

  • Ron says:

    " performed a prick test on the girl, where they give a small prick". Hadn't the girl suffered enough?

  • Kevin says:

    When I wrote about this a couple weeks ago, I found a paper where they suspected transmission of an allergen in semen because of a paper they referenced from like the 70's, and it seemed like the idea that this could happen was well known. I think the authors for this paper's claim to have the first ever case is pretty clearly false.

  • namnezia says:

    I'm skeptical. If this girl was so allergic to trace amounts, how do they know the boyfriend didn't contaminate his semen samples during his "manual extraction" with trace amounts of nuts that were in his hands from having just eaten the nuts? Was he wearing gloves while he ate the nuts? Did he wash his hands before the extraction?

  • S.C. says:

    "I have to say I’m a little surprised we haven’t heard of this before. Maybe in most long stable relationships, the partner of the person with the allergy is a little more likely to give up eating the allergen?"

    Or the amount of allergen present is often so small that the gal's reaction is usually mild. She wouldn't need to go to the doc for a mild reaction. And really, if you don't need to go, how many of us would want to, when we'd have to share exactly how we came into contact with the allergen? ;-D

    ...and I say this as someone who has actually had this happen with wheat, more than once. Mild reactions, no WAY I'm going to the doctor for those, LOL. At this point, my hubby just doesn't eat any wheat for 24 hours before we, eh, have some alone time.

    • Dani says:

      Wow. The wheat answer exactly what I was looking for! I am Celiac
      And had oral sex with my sig. Other the other day, after which I got
      violently sick, even though I KNOW I hadn't come in contact with
      gluten myself. His semen was only thing I could come up with, but
      felt weird about mentioning. Thanks :0)

  • [...] have a nut allergy, don’t let your partners eat them nuts, because, if they do, you might get an allergic reaction from their [...]

  • Shala says:

    I am allergic to wheat and I can tell when my husband has eaten it. I feel ill and itch like crazy for two days after sex. Now I have proof!!! He didn't believe me.

  • [...] from many sources which have never once tested it. However, once again, we can look nuts. A couple nut case studies were on women who had reacted to fluids from their boyfriends after those boyfriends ate nuts. [...]

  • Sucker says:

    I have an allergy to strawberries and to sulfa drugs. When my boyfriend eats strawberries, I will get a rash if his semen touches my skin, and have a mild reaction if I swallow. Also, when he was on Septra for pneumonia and I swallowed, I ended up breaking out in a petecheal rash, just like I do if I am exposed to Septra/sulfonomides. I am also allergic to nutrasweet/aspartame, but I've never dated anyone who drinks diet sodas, but I imagine it would be similar. I'm glad I read this, so I know I'm not "the only one." lol

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