This rare but underdiagnosed allergy isn't triggered by sperm cells, but by proteins in the seminal plasma – the fluid that carries sperm. First documented in 1967, when a woman was hospitalised after a "violent allergic reaction" to sex, SPH is now recognised as a type 1 hypersensitivity, the same category as hay fever, peanut allergy, and cat dander.
Symptoms range from mild to severe. Some women experience local reactions: burning, itching, redness, and swelling of the vulva or vagina. Others develop full-body symptoms: hives, wheezing, dizziness, runny nose and even anaphylaxis, a potentially life-threatening immune response.