Hi Jun,   Your partner may be allergic to protein in your semen (or seminal fluid). Semen allergy has been described and studied at a few research centers in America.   Having intercourse with other partners is not related to increased risk of causing a reaction to semen. Your partner may be hypersensitive to protein unique to your semen, or protein common to seminal fluid in many males.   Reaction to a topical you have applied to your skin may also result in your partner having vaginal irritation or an allergic reaction. Dietary factors (food you consume) are less likely to be the cause.   If use of a condom resolves the problem, semen allergy is more likely the problem.   Incubation times of sexually transmitted diseases vary based on the infectious agent. The majority of such infections would not cause the immediate type of reaction that occurs in the setting of semen allergy.   Thank You For Your Question,   J. Thompson, MD