Wondering Why Some Periods Are Lighter Than Others? Gynecologists Explain

If you're someone who menstruates, you already know that everyone's cycle is unique to them. And even then, your own cycle can fluctuate from running like clockwork to showing up at the most inopportune time. Some irregularity is, more often than not, not a major cause for concern. Stress, hormones, medications, even a change to your workout schedule or routine can all affect your flow. But, if you've been wondering "why is my period so light this month?" for quite a few cycles now, we've got you covered.

As it happens, an unusually light period is one of the most common reasons people book in to see their OBGYN. So, we went straight to the source and asked gynecologists Dr. Alyssa Dweck and Dr. Sara Twogood to explain some of the reasons a period might be or become extremely light. Read on for what they had to say.

What Is a Light Period?

The term ‘light period’ can refer to both the length of the period—fewer bleeding days than normal—and/or lighter bleeding and spotting. Metrically, a light period will usually not exceed more than 10mL per day (that equates to a maximum of two tampon changes), but can be as little as spotting here and there. Again, this is unique to every body, so a light period might mean a shorter duration to one person and lighter in volume to another or maybe it's a combination of both.

Common Causes of a Light Period

Many of the causes are very common and totally normal, whereas a few rarer ones may require further investigation.

Contraceptives

"Contraceptives, including birth control pills, the hormonal IUD, the patch, or the shot can lighten or even eliminate your flow,” says Dr. Dweck. In such instances, usually, a light period is no cause for alarm. For example, your period on birth control (also referred to as ‘withdrawal bleeding’) is usually lighter than your cycle is when not on contraceptives.

Pregnancy

Spotting or a very light period in early pregnancy is commonly mistaken for “just a light period,” says Dr. Twogood. “Taking a pregnancy test is a simple and easy way to rule this out.”

Other Common Causes

Whether we realize it or not, diet, exercise, and even our thyroid function can lead to lighter periods. “Things to eliminate are an under or overactive thyroid, which can cause changes to your flow, and even stress, which can trigger a loss of your period at times,” explains Dr. Dweck. “Other factors include rapid weight loss, an eating disorder, or excessive exercise, all of which can interfere with the regularity of your period.” 

Alongside this, there are also side effects of non-contraceptive hormones. “Some people use progestins (used in cases such as hormone therapy) to control unscheduled or irregular bleeding, and continuous use of these can make your period very light," says Dr. Twogood.

Less Common Causes of a Light Period

• Endometrial shedding: “When ovulation is irregular, such as with polycystic ovary syndrome (PCOS) or perimenopause, endometrial shedding—a cause of light periods—can occur," says Dr. Twogood. “A very light period may be from ovulation not occurring in the first place, meaning the normal hormonal fluctuations of the menstrual cycle that tell the endometrium to build up and then release for a period are not present.” Instead, the endometrium builds up but then bleeds irregularly.
• Circulating estrogen: A decrease in circulating estrogen can also lead to light periods. “Estrogen plumps up the endometrium, so if estrogen is low, that lining doesn’t plump up and results in less bleeding,” says Dr. Twogood. “Low estrogen can be the result of the likes of perimenopause, menopause, or a precursor to a condition called functional hypothalamic amenorrhea (FHA).” FHA is a form of amenorrhea, meaning the absence of a period for those of menstruating age.
• Scarring: Although uncommon, scarring inside of the uterus and cervix can cause lighter periods. “With scarring of the uterus, also known as Asherman's, the endometrium lining of the uterus that builds up every month and then bleeds with a period doesn’t build up, leading to less endometrium and therefore less bleeding,” Dr. Twogood explains. “Scarring is rare and not something that happens spontaneously, usually occurring from an unfortunate consequence of pregnancy complications, an intrauterine infection such as STIs, or from instrumentation when performing a dilation and curettage, difficult IUD placement, or biopsy of the lining of the uterus.” Scarring of the cervix is another cause of lighter periods. “If the cervix is scarred, the blood won’t be released into the vagina, and although it’s rare, it carries risks, such as pregnancy complications.”

When Is a Light Period Cause for Concern?

More often than not a light period isn't an indication of anything serious, although Dr. Dweck does advise to have an evaluation if it becomes persistent.“ It may be a good idea to undergo a thorough history with a physical exam, blood work to test your hormone levels, prolactin, and thyroid function, and even a pelvic ultrasound for evaluation.”

Alongside this, she suggests ruling out pregnancy. “If there’s a chance you might be pregnant, then first take a home pregnancy test, and if that’s negative then it’s wise to check in with your gynecologist after two to three light cycles.”

When Should You See a Doctor?

As outlined, a light period can occur for various reasons, most of which won’t necessarily require a trip to the doctor. “It all depends on risk factors and other symptoms. For example, someone who just started taking birth control pills is unlikely to require an evaluation for a light period because it is expected,” says Dr. Twogood.

On the other hand, there are a few red flags to look out for, such as increasing or persistent pain, which should never be ignored. “Most of the time a light period is not an emergency, but if your light period is ongoing, it’s safer to check in with your doctor to relieve any worry," says Dr. Twogood.

The Takeaway

Contraceptive pills, pregnancy, hormonal imbalances, and even internal scarring can cause a light period, and in most cases, it's no cause for concern. “These days, we treat the menstrual cycle almost like a window into general health,” says Dr. Dweck. "People who menstruate are usually keenly aware of what’s normal for them, especially with apps that monitor menstruation, so really any persistent or notable change in the normal cycle should be evaluated.” Bottom line: If something feels 'off' with your body, get yourself checked out for peace of mind.