Bleeding between periods, often called intermenstrual bleeding or spotting, is common and usually not dangerous. The causes range from a temporary hormone shift during ovulation to birth control side effects, infections, or structural changes in the uterus. Light spotting that happens once or twice is rarely a concern, but bleeding that recurs over multiple cycles or gets heavier deserves a closer look.
Spotting vs. Bleeding: How to Tell the Difference
The biggest distinction is volume. Spotting produces small amounts of blood that don’t require a pad or tampon. It’s often lighter in color than period blood, which tends to be darker. If you notice a few streaks of pinkish or light red blood on your underwear or when you wipe, that’s spotting.
Timing and symptoms help too. You generally know when your period is due and what it feels like. If bleeding shows up off-schedule and isn’t accompanied by your usual premenstrual symptoms (breast tenderness, cramping, bloating), it’s likely spotting rather than an early period. That said, the line between “spotting” and “abnormal bleeding” isn’t always crisp. If you’re filling a pad or the bleeding lasts more than a couple of days, treat it as something worth investigating even if it doesn’t match your normal period pattern.
Ovulation Spotting
The most common harmless explanation is ovulation. In the days leading up to ovulation, estrogen rises steadily. Once the egg is released (roughly mid-cycle for most people), estrogen dips and progesterone starts climbing. That sudden shift can destabilize a small area of the uterine lining, causing a day or two of light spotting. It’s typically pink or light brown, much lighter than a period, and resolves on its own. If you track your cycle, you’ll notice it tends to show up around the same point each month, usually 10 to 16 days before your next period.
Birth Control and Breakthrough Bleeding
Hormonal contraceptives are one of the most frequent causes of mid-cycle bleeding, especially when you’ve recently started or switched methods. The synthetic hormones in pills, patches, rings, IUDs, and implants change the thickness and stability of your uterine lining, and your body needs time to adjust.
How long that adjustment takes depends on the method. With hormonal IUDs, spotting and irregular bleeding are common in the first few months but typically improve within two to six months, according to the American College of Obstetricians and Gynecologists. With the implant, the pattern is different: whatever bleeding pattern you experience in the first three months is generally what you can expect going forward. If breakthrough bleeding on the pill bothers you, it often settles after two to three cycles, but skipping pills or taking them at inconsistent times can trigger it at any point.
Infections and Pelvic Inflammatory Disease
Sexually transmitted infections, particularly chlamydia and gonorrhea, can inflame the cervix and make it bleed easily, sometimes after sex and sometimes spontaneously between periods. Left untreated, these infections can travel upward into the uterus and fallopian tubes, causing pelvic inflammatory disease (PID).
PID doesn’t always announce itself with obvious symptoms. Some people notice bleeding between periods, unusual discharge, or a dull ache in the lower abdomen. Others have no symptoms at all until the infection has already caused damage. This is one reason routine STI screening matters, especially if you have a new sexual partner. PID is treatable with antibiotics, but scar tissue from delayed treatment can lead to long-term fertility problems.
Uterine Polyps and Fibroids
Structural growths inside the uterus are another common culprit. Uterine polyps form when cells in the uterine lining overgrow, creating small, usually benign projections. They’re estrogen-sensitive, meaning they grow in response to estrogen circulating in the body, and they’re most common in people approaching or past menopause. Polyps can cause irregular bleeding, very heavy periods, or spotting between cycles.
Fibroids, which are muscular growths in the uterine wall, can do the same thing depending on their size and location. A fibroid that presses into the uterine cavity is more likely to cause bleeding than one that grows outward. Both polyps and fibroids are usually discovered during an ultrasound and can often be removed with a minor procedure if they’re causing problems.
Thyroid Problems and PCOS
Your thyroid and your menstrual cycle are more connected than most people realize. An underactive thyroid (hypothyroidism) disrupts the hormones that regulate ovulation and can lead to irregular periods, breakthrough bleeding, and a thinner uterine lining. Thyroid hormones directly affect endometrial tissue, and when levels are off, the lining becomes less stable between periods.
Hypothyroidism also promotes insulin resistance, which is a central feature of polycystic ovary syndrome (PCOS). In PCOS, elevated insulin levels push the ovaries to produce excess androgens (male-type hormones), which interfere with regular ovulation. Without consistent ovulation, progesterone levels stay low, and the uterine lining builds up unevenly. The result can be long gaps between periods followed by heavy bleeding, or unpredictable spotting throughout the cycle. If you have other signs of either condition, such as fatigue, weight changes, thinning hair, or acne, mention them to your provider. A simple blood test can check your thyroid function and hormone levels.
Perimenopause
If you’re in your late 30s or 40s and your bleeding pattern has started to shift, perimenopause is a likely explanation. During this transition, the ovaries gradually produce less estrogen. Some months they release an egg normally; other months they don’t. That inconsistency creates unpredictable cycles. Your periods may come closer together or further apart, last longer or shorter, and vary in heaviness from one month to the next. Spotting between periods fits right into this pattern.
Perimenopause can last several years before menopause (defined as 12 consecutive months with no period). While irregular bleeding during this phase is expected, new or heavy bleeding after age 45 still warrants an evaluation to rule out polyps, thickened endometrial lining, or other causes that become more common with age.
When Bleeding Signals Something Urgent
Most intermenstrual spotting isn’t an emergency, but a few situations are. Heavy bleeding that soaks through a pad in an hour, especially when paired with dizziness, lightheadedness, or feeling faint, means your body may be losing blood faster than it can compensate. Severe pelvic pain combined with spotting in early pregnancy could indicate an ectopic pregnancy, where a fertilized egg implants outside the uterus. A ruptured ectopic is a surgical emergency. Some people also experience sudden shoulder pain from internal bleeding irritating the diaphragm, which is a less obvious but important warning sign.
If you have a positive pregnancy test (or think you might be pregnant) and develop one-sided pelvic pain with spotting, get evaluated quickly rather than waiting to see if it resolves.
How the Cause Is Found
Figuring out why you’re bleeding between periods usually starts with a pelvic exam and some basic lab work. Your provider will likely order a complete blood count to check for anemia or infection, a pregnancy test, and STI screening. Depending on your age and symptoms, additional steps may include an ultrasound to look at the uterine lining and ovaries, a hysteroscopy (a thin camera inserted through the cervix to view the inside of the uterus), or an endometrial biopsy, where a small tissue sample is taken and examined under a microscope.
Keeping a record of your bleeding before your appointment helps more than you might expect. Note the dates, how heavy the bleeding was, whether it followed sex or exercise, and any other symptoms like pain or unusual discharge. That timeline often points toward the cause faster than any single test.