Daily spotting has a wide range of causes, from hormonal birth control adjustments to structural changes in the uterus. Light bleeding between periods (called intermenstrual bleeding) is one of the most common gynecological complaints, and while it’s often harmless, persistent daily spotting that lasts more than a few weeks deserves investigation. The cause depends heavily on your age, whether you use hormonal contraception, and how long the spotting has been going on.
Hormonal Birth Control Is the Most Common Cause
If you recently started or switched a hormonal contraceptive, daily spotting is extremely common. Roughly 40% of people who use progestin-only pills experience irregular bleeding during the first three to six months. The same applies to hormonal IUDs, implants, and combination pills. Your uterine lining is adjusting to a new hormonal environment, and it can shed small amounts of tissue unpredictably during that transition.
The subdermal implant causes irregular spotting frequently enough that it’s considered a normal side effect, though about 20% of users eventually stop bleeding altogether. For most hormonal methods, the spotting tends to taper off after the first three to six months. If it doesn’t, or if it gets heavier, your provider may suggest switching methods or adjusting your dose.
Missed pills are another frequent trigger. Even being a few hours late with a progestin-only pill can cause a small drop in hormone levels, prompting a bit of breakthrough bleeding. If you’re spotting daily and occasionally forget doses, that inconsistency is the likely culprit.
Thyroid Problems and PCOS
Two endocrine conditions are strongly linked to persistent spotting: hypothyroidism (an underactive thyroid) and polycystic ovary syndrome (PCOS). Both disrupt the balance between estrogen and progesterone that keeps your cycle predictable.
An underactive thyroid can cause spotting between periods, irregular cycles, and heavier-than-normal flow. The mechanism is complex: low thyroid function raises levels of a brain hormone called prolactin, which in turn disrupts the signals that control ovulation. Without regular ovulation, progesterone stays low, and the uterine lining sheds unevenly. PCOS works through a similar hormonal imbalance. Excess androgens interfere with ovulation, leading to unpredictable estrogen and progesterone levels and frequent spotting or irregular bleeding. If you also have symptoms like fatigue, weight changes, acne, or thinning hair, a hormonal workup can identify or rule out these conditions with a simple blood draw.
Polyps and Fibroids
Structural growths inside the uterus are another common explanation for daily spotting, especially if you’re over 30. Endometrial polyps form from an overgrowth of the tissue that lines the uterus. They’re usually benign, but they create fragile, blood-vessel-rich surfaces that bleed easily and irregularly. Uterine fibroids, which are noncancerous muscular growths, can do the same thing, particularly when they grow close to the uterine lining.
Polyps and fibroids often coexist. The spotting they cause tends to be persistent and doesn’t follow a pattern tied to your cycle. It might show up as light brown or pink discharge on a liner every day, sometimes worsening around your period. These growths are typically found on a transvaginal ultrasound, and if they’re confirmed, removal is straightforward and usually resolves the bleeding.
Infections That Cause Spotting
Sexually transmitted infections, particularly chlamydia and gonorrhea, can inflame the cervix and cause light daily bleeding. This is especially likely if the spotting is accompanied by unusual discharge, a bad odor, pain during sex, or burning with urination. Left untreated, these infections can progress to pelvic inflammatory disease (PID), an infection of the reproductive organs that also causes bleeding between periods along with lower abdominal pain and sometimes fever.
The tricky part is that many cervical infections cause no obvious symptoms beyond the spotting itself. If you’re sexually active and the daily spotting started without an obvious hormonal explanation, STI testing is a reasonable step even if you feel fine otherwise.
Blood Thinners and Other Medications
Anticoagulants (blood thinners) are a well-documented cause of abnormal uterine bleeding. About 70% of menstruating women on oral anticoagulants experience heavier or more irregular bleeding, including spotting between periods. If you started a blood thinner and then noticed daily spotting, the medication is very likely involved. Don’t stop taking it on your own, but bring it up with your prescriber so they can weigh options.
Other medications that can trigger spotting include certain antidepressants, corticosteroids, and herbal supplements like ginseng or soy isoflavones that have mild estrogenic effects.
Perimenopause and Shifting Hormones
If you’re in your 40s (or sometimes late 30s), daily spotting may be one of the earliest signs of perimenopause. As ovarian function gradually winds down, cycles become less regular, and fluctuating estrogen levels can cause the uterine lining to shed in small, unpredictable amounts. This phase can last several years before periods stop entirely.
Perimenopausal spotting is common, but it also overlaps with the age range where more serious causes become relevant. Current guidelines recommend a transvaginal ultrasound as the first step for evaluating abnormal bleeding in this age group. If the uterine lining measures 4 mm or less on ultrasound, the chance of endometrial cancer is less than 1%. Thicker linings, persistent bleeding, or inconclusive imaging typically lead to further testing like an endometrial biopsy or hysteroscopy.
When Spotting Signals Something Serious
Endometrial cancer presents as irregular vaginal bleeding in more than 90% of postmenopausal cases, and bleeding between periods is a recognized early symptom at any age. This doesn’t mean daily spotting is likely to be cancer. It does mean that spotting persisting for weeks without a clear explanation warrants evaluation, especially if you have risk factors like obesity, type 2 diabetes, PCOS, a history of irregular ovulation, or a family history of gynecologic cancers.
Any vaginal bleeding after menopause (defined as 12 consecutive months without a period) should be evaluated promptly, even if it’s light. Endometrial sampling or ultrasound can quickly rule out precancerous changes.
What the Evaluation Looks Like
If you see a provider about daily spotting, the workup is usually straightforward. It starts with a detailed history of your cycle, contraceptive use, and other medications. A physical exam including a speculum examination helps rule out cervical or vaginal sources of bleeding. From there, the most common next step is a transvaginal ultrasound to look at the uterine lining and check for polyps or fibroids.
Blood work may include a pregnancy test, thyroid hormone levels, and a complete blood count if the spotting has been heavy or prolonged enough to cause anemia. STI screening is added when clinically relevant. If the ultrasound shows a thickened lining or a visible growth, your provider may recommend a saline-infusion sonogram for a clearer image, an office endometrial biopsy, or a hysteroscopy where a small camera is used to look inside the uterus directly.
For most people, the cause turns out to be hormonal or structural and is manageable with a medication change, hormonal treatment, or a minor procedure. The key variable is how long it’s been going on: spotting for a few days after starting new birth control is expected, while spotting every day for several weeks or months without explanation is worth investigating sooner rather than later.