Spotting between periods can mean different things at early versus later stages of your reproductive cycle.
When you first start having your period, it may be quite irregular for months or even years. This is because your brain, ovaries, and uterus are still working on getting in sync hormonally. Unless your bleeding is excessively heavy or prolonged, it’s usually not a problem.
Once you become sexually active, spotting after intercourse raises a red flag. This is especially true if you’re having unprotected sex or have just started having sex with a new partner.
Bleeding can signal a sexually transmitted infection (STI), such as chlamydia or gonorrhea, that should be treated promptly. Often, the cervix can be very friable [eroded] or just bleed very easily from the infection.
Another condition that can lead to bleeding after intercourse is cervical entropion, in which the fragile glandular cells lining the cervical opening grow on the surface of the uterus.
Much more rarely, post-sex spotting can be a sign of cervical cancer. Your doctor can take a Pap smear, a sample of cells from your cervix (the opening of the uterus at the top of the vagina) to test for STIs and abnormal precancerous or cancerous cells.
Mid-cycle bleeding could also mean that you’re pregnant and could be miscarrying, although spotting during pregnancy doesn’t always mean the pregnancy will be lost. Ectopic pregnancy, in which a fertilized egg grows outside of the uterus (usually within the fallopian tubes), can also cause bleeding, according to the American Congress of Obstetricians and Gynecologists (ACOG).
Spotting may also be due to vaginal trauma. The vagina and the cervix are very vascular [they have a lot blood vessels], so they bleed very easily. A scratch in the vagina will always bleed more than a scratch in your regular skin would.