My girlfriend is getting hives after we have sex?

Interesting: Well, she's likely contacting something she's allergic to. Maybe the condom(latex) or the gel or your cologne, hairgel, something you just ate that's on your lips (peanuts), etc. Rarely some people will get hives when they exercise.

Allergy to seminal: Fluid can trigger hives, asthma & even anaphylaxis in some women. Dr. Holt covered other possible causes of hives after intercourse. This is definitely a problem calling for a trained allergist.