Imagine experiencing itching, burning, swelling, or even difficulty breathing just moments after sexual intercourse. For a small but growing number of individuals, this isn’t just an awkward anecdote—it’s a medical condition known as seminal plasma hypersensitivity (SPH), an allergy to semen.
This rare yet underdiagnosed allergy is not triggered by sperm cells, but by proteins in the seminal plasma—the fluid that carries sperm. First documented in 1967 when a woman was hospitalized following a “violent allergic reaction” to sex, SPH is now classified as a type 1 hypersensitivity, similar to hay fever, peanut allergies, and reactions to cat dander.
Understanding Seminal Plasma Hypersensitivity
Symptoms of SPH can range from mild to severe. Some individuals experience local reactions such as burning, itching, redness, and swelling of the vulva or vagina. Others may develop systemic symptoms including hives, wheezing, dizziness, runny nose, and even anaphylaxis, a potentially life-threatening immune response.
Until 1997, SPH was believed to affect fewer than 100 women worldwide. However, a study led by allergist Jonathan Bernstein revealed that among women reporting postcoital symptoms, nearly 12% could be classified as having probable SPH.
“In a small, unpublished survey conducted in 2013, I found a similar 12% rate. The true figure may be higher still, as many cases go unreported, misdiagnosed, or dismissed as sexually transmitted infections, yeast infections, or general ‘sensitivity’. One revealing clue: symptoms disappear when condoms are used.”
A 2024 study reinforced these findings, suggesting that SPH is both more common and more frequently misdiagnosed than previously believed.
The Allergens Behind SPH
The primary allergen appears to be prostate-specific antigen (PSA), a protein found in all seminal plasma, not just that of a particular partner. This means women can develop a reaction to any man’s semen, not just their regular partner’s.
There is also evidence of cross-reactivity. For example, Can f 5, a protein found in dog dander, is structurally similar to human PSA. Women allergic to dogs may find themselves reacting to semen as well. In one unusual case, a woman with a Brazil nut allergy broke out in hives after sex, likely due to trace nut proteins in her partner’s semen.
Diagnosis typically begins with a detailed sexual and medical history, often followed by skin prick testing with the partner’s semen or blood tests for PSA-specific antibodies (IgE). Research involving symptomatic women has demonstrated that testing with washed spermatozoa, free from seminal plasma, can help confirm that the allergic trigger is not the sperm cells themselves, but proteins in the seminal fluid.
Men and Semen Allergies
Interestingly, it’s not just women who are affected. Some men may be allergic to their own semen, a condition known as post-orgasmic illness syndrome (POIS). This condition causes flu-like symptoms such as fatigue, brain fog, and muscle aches immediately after ejaculation. It is believed to be an autoimmune or allergic reaction. Diagnosis can be challenging, but skin testing with a man’s own semen can yield a positive reaction.
Implications for Fertility
While seminal plasma hypersensitivity does not cause infertility directly, it can complicate conception. Avoiding the allergen—usually the most effective treatment for allergies—is not feasible for couples trying to conceive. Treatments include prophylactic antihistamines, anti-inflammatories, and desensitization using diluted seminal plasma. In more severe cases, couples may opt for in vitro fertilization (IVF) with washed sperm, bypassing the allergic trigger altogether.
It’s crucial to note that SPH is not a form of infertility. Many women with SPH have conceived successfully, some naturally and others with medical support.
Raising Awareness
Despite its impact, SPH remains largely unknown. Sex-related symptoms often go unspoken due to embarrassment, stigma, and a lack of awareness among healthcare providers. In Bernstein’s 1997 study, nearly half of the women who experienced symptoms after sex had never been checked for SPH, and many had spent years being misdiagnosed and receiving incorrect treatment.
“If sex routinely leaves you itchy, sore, or unwell—and condoms help—you might be allergic to semen. It’s time to bring this hidden condition out of the shadows and into the consultation room.”
This article is republished from The Conversation under a Creative Commons license. Read the original article by Michael Carroll, Reader/Associate Professor in Reproductive Science at Manchester Metropolitan University.
