Frequent spotting between periods is one of the most common gynecological complaints, and it almost always traces back to one of a handful of causes: hormonal shifts, birth control, structural changes in the uterus, infections, or early pregnancy. The tricky part is that spotting can look the same on your underwear regardless of what’s behind it, so understanding the context (your age, medications, sexual activity, and other symptoms) is what narrows it down.
Hormonal Birth Control Is the Most Common Culprit
If you’re on hormonal contraception, that’s the first place to look. Breakthrough bleeding happens more often with low-dose and ultra-low-dose birth control pills, the implant, and hormonal IUDs. The reason is straightforward: these methods thin your uterine lining by keeping hormone levels steady and low. When levels dip even slightly, small patches of that thin lining can shed, producing light spotting.
How long this lasts depends on the method. With an IUD, spotting and irregular bleeding are common in the first months after placement but typically improve within two to six months. The implant works differently: whatever bleeding pattern you have in the first three months is generally the pattern you’ll have going forward. So if you’re three months into an implant and still spotting frequently, that’s likely your new normal rather than a phase that will resolve on its own.
Skipping pills, starting a new pack late, or switching between methods can also trigger spotting. When hormone levels drop suddenly, even briefly, your body responds by shedding a small amount of uterine lining. This is sometimes called withdrawal bleeding, and it’s lighter than a real period because there’s less lining built up to shed.
Hormonal Shifts Without Birth Control
Even without contraception, your hormones can fluctuate enough to cause spotting. Stress, significant weight changes, thyroid problems, and irregular ovulation all affect the balance between estrogen and progesterone. When ovulation doesn’t happen on schedule (or doesn’t happen at all in a given cycle), progesterone levels stay low, and the uterine lining can shed in small, unpredictable amounts rather than all at once during a period.
An underactive thyroid is a particularly common and overlooked cause. Low thyroid function slows down the hormonal signaling that regulates your cycle, leading to spotting, heavier periods, or cycles that vary widely in length. A simple blood test can identify this.
Spotting During Perimenopause
If you’re in your 40s or early 50s and noticing more spotting than usual, perimenopause is a likely explanation. During this transition, ovulation becomes less predictable, and hormone levels swing more dramatically from month to month. You might skip periods, have heavier flow, or notice spotting between cycles. All of these reflect the same underlying instability in estrogen and progesterone.
That said, not all perimenopausal bleeding is harmless. Spotting between periods, bleeding after sex, and periods that are significantly heavier or longer than your usual pattern all warrant a conversation with your doctor, even if perimenopause seems like the obvious answer. These symptoms overlap with conditions like polyps or, less commonly, precancerous changes that become more relevant with age.
Any vaginal bleeding after menopause (defined as 12 consecutive months without a period) should always be evaluated, regardless of how light it is.
Polyps and Fibroids
Uterine polyps are small growths that form when cells in the uterine lining overgrow. They attach to the inner wall of the uterus by a base or a thin stalk, and they’re sensitive to estrogen, meaning they grow in response to your body’s natural hormone levels. Polyps are a well-known cause of bleeding between periods, unusually heavy periods, and spotting after sex.
Fibroids are noncancerous muscular growths in or on the uterus. They’re extremely common, especially in your 30s and 40s, and can cause spotting depending on their size and location. Fibroids that grow into the uterine cavity (called submucosal fibroids) are the most likely to cause irregular bleeding because they distort the lining directly.
Both polyps and fibroids are typically identified with a transvaginal ultrasound. If the ultrasound isn’t conclusive, your doctor may recommend a procedure that uses saline to get a clearer view of the uterine cavity, or direct visualization with a tiny camera.
Infections and Cervical Irritation
Sexually transmitted infections like chlamydia and gonorrhea can cause inflammation of the cervix or, if left untreated, pelvic inflammatory disease (PID), an infection that spreads to the uterus and surrounding reproductive organs. Spotting between periods and pain or bleeding during sex are hallmark symptoms of PID, though many people with early cervical infections have no symptoms at all.
Non-sexually transmitted infections and general cervical inflammation (cervicitis) can also cause spotting, particularly after intercourse. If your spotting tends to show up after sex, cervical irritation from infection, dryness, or even a recent pelvic exam or biopsy is worth considering.
Could It Be Implantation Bleeding?
If there’s any chance you could be pregnant, light spotting about 10 to 14 days after ovulation may be implantation bleeding. This happens when a fertilized egg attaches to the uterine wall, and it has a distinct profile that’s different from a period. Implantation bleeding is pink or brown (not bright or dark red), very light in flow (more like discharge than menstrual blood), and shouldn’t soak through a pad. It typically lasts a few hours to about two days.
Because implantation bleeding falls right around when you’d expect your period, it’s easy to confuse the two. A pregnancy test taken a few days after the bleeding stops will usually give you a clear answer. Heavy bleeding, clots, or bright red blood during early pregnancy is not typical implantation bleeding and needs prompt medical attention.
Less Common but Important Causes
Blood-thinning medications can cause spotting by making it harder for small blood vessels in the uterine lining to clot normally. If you started an anticoagulant and noticed new spotting, that connection is worth raising with your prescriber.
Cervical or uterine cancer can cause abnormal bleeding, though this is far less common than the other causes on this list. The risk increases with age, and it’s one reason why new or changing bleeding patterns in people over 40, and especially after menopause, are taken seriously. Precancerous changes to the cervix (often detected through Pap smears) can also cause spotting.
What to Expect at a Doctor’s Visit
Evaluation for persistent spotting usually starts with your medical history: your age, cycle patterns, contraception use, sexual activity, and any other symptoms like pain or fatigue. From there, the workup is guided by what seems most likely. Common next steps include a pregnancy test, blood work to check hormone and thyroid levels, STI screening, and a transvaginal ultrasound to look for structural issues like polyps or fibroids.
If you have risk factors for endometrial problems (irregular cycles over a long period, obesity, age over 45, or a family history), your doctor may recommend an endometrial biopsy, a quick in-office procedure that samples the uterine lining. If imaging suggests something unusual but isn’t conclusive, more detailed views through hysteroscopy or, rarely, MRI may follow.
Spotting that soaks through a pad or tampon every hour for more than four hours crosses the line from spotting into heavy bleeding and needs urgent evaluation. The same applies to any bleeding during a confirmed pregnancy.