A burning feeling after semen enters the vagina is often related to irritation, infections or friction caused by lack of lubrication. Semen has a more alkaline pH than the vagina, which can temporarily disrupt the vaginal environment and cause discomfort, especially if the tissue is already sensitive. Infections such as yeast infections, bacterial vaginosis or trichomoniasis can also make the area more prone to burning.
Less commonly, burning may be caused by an allergy to proteins in semen. This usually causes burning, itching, redness or swelling within minutes of contact and tends to improve when a condom is used. If the burning gets worse with condoms, it may be a reaction to latex, lubricants or spermicides instead. Intimate soaps and other products can also cause irritation.
Other possible causes include sexually transmitted infections, such as chlamydia, gonorrhea or herpes, and urinary tract infections, especially if burning occurs when urinating after sex.
Go to the emergency room right away if you develop hives across your body, swelling of the face or lips, or difficulty breathing after contact with semen.
See a gynecologist if burning lasts for hours or days, keeps coming back, or comes with discharge, itching, a bad odor or pain. Avoid self-treating without knowing the cause, and use condoms until you are evaluated.