Bleeding during sex can occur for several reasons, most commonly related to the cervix and vaginal tissue. Some common causes include:

• Irritation or infection of the cervix (cervicitis), often caused by sexually transmitted infections like chlamydia or gonorrhea, or non-STD infections like yeast infections.
• Cervical polyps, small benign growths on the cervix that can bleed when irritated.
• Vaginal dryness or insufficient lubrication, which can cause friction and minor tears during intercourse.
• Cervical ectropion, a condition where fragile cells from inside the cervix extend to the outer surface, making it prone to bleeding.
• Rough or vigorous sex causing vaginal tearing or trauma.
• Hormonal birth control changes affecting bleeding patterns.
• Other less common causes like uterine prolapse, precancerous or cancerous changes in the cervix or uterus, pelvic inflammatory disease, or incorrectly placed intrauterine devices (IUDs).

If the bleeding is light, occasional, and not accompanied by pain or other symptoms, it may not be serious. However, persistent, heavy, or recurrent bleeding, or bleeding with pain, unusual discharge, or other symptoms should be evaluated by a healthcare professional to rule out infections, growths, or more serious conditions.