Spotting between periods is common, affecting up to 35% of women of reproductive age at some point. It can range from a few drops of blood on your underwear to light staining that lasts a day or two. The causes span from completely harmless hormonal shifts to infections or structural changes in the uterus that need treatment.
Hormonal Birth Control
Hormonal contraceptives are one of the most frequent causes of spotting, and it can happen with any type: pills, patches, rings, implants, or hormonal IUDs. Breakthrough bleeding is especially common with low-dose and ultra-low-dose birth control pills, implants, and hormonal IUDs. The synthetic hormones in these methods thin the uterine lining, which can become fragile enough to shed small amounts of blood at unpredictable times.
If you have an IUD, spotting and irregular bleeding are typical in the first few months after placement. This usually improves 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 your pattern going forward. So if you’re still spotting after that initial window, it’s worth talking to your provider about whether a different method might suit you better. Missing a pill, taking it at inconsistent times, or starting a new prescription can also trigger spotting that resolves once your body adapts.
Ovulation Spotting
Some women notice light spotting right around the middle of their cycle, which corresponds to ovulation. In a 28-day cycle, this typically happens around day 14. The rapid rise in estrogen followed by a brief dip just before ovulation can cause a small amount of the uterine lining to shed.
Ovulation spotting is much lighter than a period. It usually shows up as a small amount of blood when you wipe, a few drops on a panty liner, or light staining on your underwear. The color is generally pink or light red, though it can occasionally appear brown. It’s not enough to need a tampon and typically lasts only a day or two. If you’re tracking your cycle and notice this pattern month after month at roughly the same point, ovulation is the likely explanation.
Implantation Bleeding
If there’s any chance you could be pregnant, the spotting may be implantation bleeding. This happens when a fertilized egg attaches to the uterine lining, typically 10 to 14 days after ovulation. Because of that timing, it often shows up right around when you’d expect your period, which makes it easy to confuse the two.
The key difference is volume and duration. Implantation bleeding is very light, usually just spotting that lasts a few hours to about two days. It won’t progress into a heavier flow the way a period does. If you have light spotting that stops on its own and your period doesn’t arrive on schedule, a pregnancy test is a reasonable next step.
Progesterone and the Luteal Phase
Even without birth control or pregnancy, your own hormonal fluctuations can cause spotting in the days before your period starts. Research published in the Journal of Clinical Endocrinology and Metabolism found that women who experienced premenstrual spotting had higher progesterone levels in the luteal phase (the second half of the cycle) and a slower decline in progesterone compared to women who didn’t spot. Essentially, when progesterone drops gradually rather than sharply, the uterine lining starts to break down unevenly, releasing small amounts of blood before your full period begins.
This type of spotting is generally harmless. It tends to appear as light brown or pink discharge in the one to two days before menstrual bleeding picks up. If it happens occasionally, it’s a normal variation in your cycle. If it becomes persistent or heavier over time, it may point to a progesterone imbalance worth investigating.
Infections
Sexually transmitted infections, particularly chlamydia and gonorrhea, can cause spotting between periods. Both infections inflame the cervix and sometimes spread to the uterus and fallopian tubes, making the tissue more likely to bleed. Chlamydia lists bleeding between periods as a recognized symptom, while gonorrhea can cause heavy bleeding between periods or heavier-than-normal menstrual flow. HPV can also cause bleeding, though it’s more commonly triggered by intercourse rather than occurring spontaneously.
The tricky part is that chlamydia and gonorrhea often cause no symptoms at all in the early stages. Spotting may be one of the first signs something is off. If you’re sexually active and noticing unexplained bleeding, especially alongside unusual discharge, pelvic pain, or burning during urination, getting tested is straightforward and the infections are treatable with antibiotics.
Uterine Polyps and Fibroids
Polyps are small, usually noncancerous growths that develop on the inner lining of the uterus. They’re a well-known cause of bleeding between periods, unpredictable cycles, and very heavy periods. Some people with polyps have only light spotting, while others are completely symptom-free and discover them incidentally during an ultrasound.
Fibroids, which are muscular growths in the uterine wall, can produce similar symptoms, particularly when they grow near or into the uterine cavity. Both polyps and fibroids become more common as you get older, especially in your 30s and 40s. The spotting they cause tends to be irregular and doesn’t follow a predictable mid-cycle or premenstrual pattern, which can help distinguish it from ovulation or hormonal spotting. Polyps are often removed with a simple in-office or outpatient procedure, while fibroids have a wider range of treatment options depending on their size and location.
Thyroid Problems and PCOS
Your thyroid gland directly affects your ovaries and interacts with the proteins that carry reproductive hormones through your bloodstream. When the thyroid is underactive (hypothyroidism), it can cause periods that are heavier, longer, or more frequent than normal. In some cases, it disrupts the cycle enough to produce bleeding at unexpected times. High levels of thyroid-releasing hormone in hypothyroidism also trigger the pituitary gland to release prolactin, a hormone that can further disrupt your cycle and lead to absent or infrequent periods.
Polycystic ovary syndrome (PCOS) affects ovulation, often causing long gaps between periods followed by unpredictable bleeding or spotting. Because PCOS involves prolonged exposure to estrogen without the balancing effect of progesterone from ovulation, the uterine lining can build up unevenly and shed at irregular intervals. Both thyroid disorders and PCOS are diagnosed with blood tests and are manageable once identified.
Perimenopause
If you’re in your 40s and noticing more frequent spotting or unpredictable cycles, perimenopause is a common explanation. During this transition, which can last several years before menopause, estrogen and progesterone levels fluctuate more erratically than they did during your reproductive years. This instability makes the uterine lining less predictable, and spotting between periods or cycles that vary significantly in length and heaviness become normal features of the transition. The two-year cumulative incidence of intermenstrual bleeding in perimenopausal women is about 24%.
Spotting After Menopause
Any vaginal bleeding after menopause, even light spotting, deserves medical evaluation. While the cause is often benign (thinning of vaginal or uterine tissue, polyps), approximately 9% of postmenopausal women who see a doctor for bleeding are eventually diagnosed with endometrial cancer. That number is high enough that clinicians treat postmenopausal bleeding as a red flag. Evaluation usually involves an ultrasound to measure the thickness of the uterine lining and, for women over 45 or those with risk factors, a tissue sample from the uterus.
What Evaluation Looks Like
If your spotting is persistent, heavy, or accompanied by pain, a provider will typically start with a pelvic exam to check for visible causes like cervical inflammation or trauma. From there, a pelvic ultrasound can reveal polyps, fibroids, or changes in the uterine lining. Blood work may include a pregnancy test, thyroid panel, and hormone levels. For women over 45, or younger women with risk factors like obesity or PCOS, a uterine tissue sample is often recommended as a first-line test to rule out precancerous changes.
Occasional light spotting that follows a recognizable pattern, like mid-cycle ovulation spotting or a day of brown discharge before your period, is rarely a cause for concern. Spotting that is new, unexplained, progressively heavier, or paired with pelvic pain or unusual discharge is worth getting checked. The evaluation process is generally quick and noninvasive, and most causes are straightforward to treat once identified.