Irregular bleeding affects nearly all women at some point during their reproductive years. Spotting refers to passage of a small amount of blood from the vagina outside of a woman’s menstrual period. This small amount of bleeding often appears as blood-tinged mucus, or red or brown vaginal discharge. Spotting after or between periods, known as intermenstrual bleeding, can occur for a variety of reasons. Possible culprits include hormone imbalances, contraceptive causes, pregnancy, infections and other reproductive disorders.
Among women who are naturally menstruating, meaning they are not using hormonal contraception, several common occurrences can lead to spotting between periods. Roughly 1 to 2 percent of women experience spotting at the time of ovulation, when a mature egg is released from the ovary. This typically occurs roughly 2 weeks after the start of the previous period and is due to a natural dip in estrogen near the time of ovulation.
Anovulatory cycles, in which the ovaries fail to produce and release a mature egg, are another common cause of irregular and intermenstrual bleeding. Occasional anovulatory cycles can occur due to illness or very stress, and commonly occur in the early and late reproductive years of a woman’s life. Hormonal conditions, such as an over- or under-active thyroid and polycystic ovary syndrome, also cause frequent anovulatory cycles.
Hormonal birth control, which suppresses a woman's natural menstrual cycle, can lead to spotting between periods. This is particularly common with low-dose combined birth control pills, progestin-only pills and depot shots. Forgetting to take one of your birth control pills is a common cause of spotting between periods.
An intrauterine device (IUD) can also cause irregular menstrual bleeding and spotting between periods. For women with a hormonal IUD (Mirena, Skyla), this side effect is most common during the first 3 to 6 months of use. Copper IUD (ParaGard) users are more likely to experience heavy bleeding than those using a hormonal IUD. Although heavy bleeding often decreases with continued use of the copper IUD, spotting or intermenstrual bleeding can persist.
Sexual intercourse sometimes causes minor bleeding that can lead to spotting. This bleeding can come from mild irritation of the vagina or cervix, the opening to the uterus at the upper end of the vagina. Vaginal irritation and minor bleeding related to intercourse is most common among women approaching menopause, who might experience vaginal dryness.
Bleeding from the cervix related to intercourse is often associated with a harmless condition called cervical ectropion. With this condition, tissue that is normally confined to the interior of the cervix extends onto the external cervical surface. This fragile tissue tends to bleed easily, such as during intercourse. Temporary cervical ectropion is common among women on hormonal birth control.
Infectious and Pregnancy-Related Causes
Infections of the female reproductive system are another possible cause of spotting between periods. Chlamydia, gonorrhea and internal genital warts can all cause low-level cervical bleeding and spotting between periods. The bleeding is often triggered by sexual intercourse. Since these conditions often cause no other symptoms, spotting might be the only tip-off.
Spotting around the time of an expected period could be an early sign of pregnancy. This type of bleeding, known as implantation bleeding, occurs when the pregnancy embeds into the uterine lining. Women who typically have light periods might mistake implantation bleeding for a normal period.
Other Reproductive System and Medical Causes
Noncancerous and, less commonly, cancerous growths can potentially cause irregular bleeding and spotting between periods, which may or may not be associated sexual intercourse. Examples include:
-- uterine fibroids
-- cervical, uterine and vaginal polyps
-- cervical, uterine and certain types of ovarian cancer
Women with bleeding disorders often experience heavy menstrual bleeding and spotting between periods. Certain medications might also be to blame, including:
-- the breast cancer drug tamoxifen (Nolvadex)
-- anticoagulants, such as warfarin (Coumadin), clopidogrel (Plavix), dabigatran (Pradaxa), apixaban (Eliquis) and rivaroxaban (Xarelto)
Next Steps and Precautions
Although some conditions that lead to spotting between periods pose no health threat, it’s best to see your doctor if you experience unexplained intermenstrual bleeding to identify the cause. Once the cause is determined, your health care provider can recommend appropriate treatment, if needed. Seek medical care right away if you experience heavy bleeding, suspect you might have been exposed to a sexually transmitted disease, or there is a possibility you might be pregnant.
Reviewed and revised by: Tina M. St. John, M.D.