Genital itching, blisters and redness are telltale symptoms of many conditions, so much so that even a physician can have a difficult time knowing where to start with a female patient. Once sexually transmitted infections (STIs) and vaginitis are ruled out, a latex allergy may be next in the line of usual suspects.

However, if a woman experiences the same symptoms while using a non-latex condom, she may be part of the small group of people who are allergic to their partner's semen. Human seminal plasma (HSP) hypersensitivity is a rare allergy afflicting up to an estimated 40,000 women in the United States.

A protein allergy

Allergies to semen operate much like any other allergy, explained Jonathan A. Bernstein, M.D., an allergy specialist.

"Seminal plasma hypersensitivity is an allergic reaction to a protein in the seminal fluid," Bernstein said. "It is not a reaction to spermatozoa. Women develop specific immunoglobulin E [an antibody] to prostate-specific antigen in their sexual