Spotting between periods has a wide range of causes, from completely harmless hormonal shifts to infections or growths that need treatment. In most cases, the explanation is something manageable, but persistent or heavy spotting deserves attention because it can occasionally signal something more serious.
Ovulation Spotting
One of the most common and benign causes is ovulation itself. Estrogen drops just after you ovulate, and for some people, that temporary dip causes a small amount of uterine lining to shed. The result is light spotting, usually pink or light brown, that lasts a day or two at most. In a typical 28-day cycle, this happens around day 14, right at the midpoint. If you notice a pattern of faint spotting roughly two weeks before your next period, ovulation is the likely explanation.
Hormonal Birth Control
Breakthrough bleeding is one of the most frequently reported side effects of hormonal contraception, especially in the first few months of use. With IUDs, spotting and irregular bleeding are common in the initial months after placement and usually improve within two to six months as your body adjusts. The implant works differently: the bleeding pattern you experience in the first three months tends to be the pattern you’ll have going forward, so if spotting is frequent early on, it may continue.
Combination pills, progestin-only pills, and the hormonal patch or ring can all trigger spotting too. Missing a pill or taking it at inconsistent times makes breakthrough bleeding more likely. If you’ve recently started, switched, or stopped a hormonal method, that’s a very common reason for unexpected bleeding.
Uterine Polyps
Polyps are soft tissue growths that form on the inner lining of the uterus. They attach to the lining by a thin stalk or a broad base and extend inward into the uterine cavity. Because they create extra surface area of endometrial tissue, they can bleed unpredictably between periods or cause heavier periods than usual.
Age is the biggest predictor. Polyps are most common in people in their 40s and 50s, around the time of perimenopause, and they can also develop after menopause. They rarely affect anyone under 20. Most polyps are noncancerous, but some can be precancerous, which is why providers often recommend removing them or at least monitoring them closely.
Infections and Pelvic Inflammatory Disease
Sexually transmitted infections, particularly chlamydia and gonorrhea, can cause spotting between periods. Other signs include unusual vaginal discharge, discharge with an odor, and painful urination. Left untreated, these infections can spread to the uterus, fallopian tubes, or ovaries, leading to pelvic inflammatory disease (PID). PID causes bleeding between periods along with pelvic pain, fever, and sometimes pain during sex. Because PID can cause lasting damage to reproductive organs, early treatment matters.
Thyroid Problems and PCOS
Your menstrual cycle depends on a careful balance of hormones, and conditions that disrupt that balance can cause irregular bleeding. Hypothyroidism (too little thyroid hormone) and hyperthyroidism (too much) both interfere with cycle regularity. Polycystic ovary syndrome (PCOS), which affects how the ovaries release eggs, is another common culprit. These conditions typically cause other noticeable symptoms too: unexplained weight changes, fatigue, acne, or excess hair growth in the case of PCOS. A simple blood test can check thyroid levels and help identify hormonal imbalances.
Perimenopause
If you’re in your late 30s or 40s and your cycles are becoming unpredictable, perimenopause is a likely factor. During this transition, estrogen and progesterone rise and fall irregularly rather than following the predictable pattern of earlier years. Ovulation becomes less reliable, which means the time between periods may get longer or shorter, your flow may swing from light to heavy, and you may skip periods entirely. Spotting between cycles fits neatly into this picture. Perimenopause can last several years before menstruation stops completely.
Gynecologic Cancers
Abnormal vaginal bleeding is a common early sign of nearly all gynecologic cancers, including endometrial and cervical cancer. This doesn’t mean spotting is likely to be cancer. The vast majority of intermenstrual bleeding is caused by something far less serious. But it is recognized as a red flag symptom, which is why it’s worth paying attention to bleeding that is new, persistent, or unusual for you. Any vaginal bleeding after menopause should be evaluated. Before menopause, periods that are heavier than normal, last longer, or come with unexpected bleeding between cycles are worth mentioning to a provider, especially if the pattern continues for more than two weeks.
Other Possible Triggers
Several less common causes round out the list. Early pregnancy, including implantation bleeding, can produce light spotting that’s easy to mistake for an irregular period. Cervical irritation from a recent Pap smear, vigorous sex, or a cervical infection can cause a small amount of bleeding. Significant stress or rapid weight changes can temporarily disrupt your hormonal cycle enough to trigger spotting. Certain medications, particularly blood thinners, can also make breakthrough bleeding more likely.
How Spotting Is Evaluated
If you see a provider about spotting, expect a conversation about your menstrual history, any medications or birth control you use, and associated symptoms like pain, bloating, or changes in discharge. From there, the workup depends on what your provider suspects. Common first steps include a pregnancy test, STI screening, and a complete blood count to check for anemia or signs of infection. You may also be tested for bleeding disorders.
If a structural cause like polyps is suspected, an ultrasound is usually the starting point. For a closer look, a provider might use hysteroscopy, which involves a thin, lighted scope passed through the cervix to visualize the inside of the uterus. An endometrial biopsy, where a small sample of the uterine lining is examined under a microscope, helps rule out precancerous or cancerous changes. More advanced imaging like MRI or CT scans is reserved for cases where initial tests don’t provide a clear answer.
Occasional, light spotting that lines up with ovulation or a new birth control method is rarely a cause for concern. Spotting that’s heavy enough to soak a pad, comes with pelvic pain or fever, recurs over multiple cycles without explanation, or appears after menopause warrants a closer look.