Periods, by nature, can vary — from person to person and even from month to month. So if you’re wondering why your period is lighter than usual this month, you certainly won’t be the first person to have questioned it. In the same way that the length of time you bleed for or day of the monthyou get your period can change, it’s also common for the amount of period blood you lose to differ. 

Sometimes, a light flow can just be part of the regular fluctuations of your period, and often a period will start light before becoming heavier. But occasionally, it can also be a signal that there’s something else going on. Here, three experts break down why, exactly, your monthly bleeding may be light and also explain how to know when it’s time to see a medical professional.

According to the International Federation of Gynecology and Obstetrics, a “light” bleed is anything less than 5 ml, which is less than a tablespoon. Light bleeding is also generally associated with a shorter duration of 1 to 2 days.

Of course, we know that this is difficult to measure. But there are other ways to establish whether or not your period is light this month, explains OB-GYN and assistant professor at Washington University School of Medicine Dr. Marta Perez. “I don’t typically tell my patients a specific amount of milliliters or ounces,” she explains. “Rather, I’d ask them how many products they used that month or if the amount of blood they shed impacted their quality of life.”

Based on Dr. Perez’s approach, if you’ve used four regular tampons or pads throughout your entire period, then you’d probably consider it “light.” That’s because, when fully saturated, a regular tampon or daytime pad can hold around 5 milliliters of blood.

Is it normal to have a light period? 

The short answer is yes. Every person is different, and so the chances of you bleeding the exact same amount as your friend, colleague, or sister is highly unlikely. It’s not just the amount of blood that can constitute a light period, however. “A light period may have fewer bleeding days or a [darker] color,” explains Dr. Perez. 

This is due to a process called “oxidation,” where blood changes when it’s exposed to oxygen as it travels from your uterus to your pad, tampon, or other menstrual product. As you’re shedding less blood, it’ll take more time, Dr. Perez explains. “The longer the blood is exposed to oxygen outside your blood vessels, the darker or browner it may appear.”

6 potential causes of a light period

While they are common, sometimes light periods can be indicators of wider health concerns and may warrant seeing a medical professional. Knowledge is power, so clue yourself up on the possible causes for a light period, which include:

1. Normal variation

Normal variation (the regular fluctuation of your period) is the most common cause for light periods, and usually even a period that feels very light for you still falls within the boundaries of a “regular” bleed. “Truly every woman is different when it comes to the amount of bleeding she has in her menstrual cycle,” explains Dr. Van Dis. That said, if you’re concerned, then schedule a checkup with your doctor or health care professional. They should be able to talk through your worries, run any tests that might be needed, and put your mind at ease.

2. Stress or external influences

If you’re going through a stressful time, it can have an impact on your menstrual cycle. “This could include stress from a relationship, work stress, or even difficulty getting to sleep,” Dr. Flanagan explains. 

Menstrual cycles can also become lighter if you change your eating or exercise habits. Generally speaking, you’ll experience lighter periods if you exercise too much and eat too little.

3. Medication or contraception effects

Many birth control options work to stabilize and sometimes even thin the lining of your uterus to prevent fertilized eggs from attaching themselves (aka pregnancy), which in turn results in shorter and lighter menstrual cycles. “Progesterone specifically — which is contained within the mini-pill, implant, IUD, and injection — can do this,” explains Dr. Flanagan. So can the combined contraceptive pill.

4. Age or perimenopause 

Many people experience lighter and less frequent periods as they approach menopause, which is defined as 12 months without a period, explains Dr. Flanagan. 

It’s worth noting here, however, that not everyone’s perimenopause works the same way. While some get lighter periods as they begin to tail off, others may experience different changes to their cycles. “They may be longer, more frequent, or heavier,” Dr. Flanagan says.

5. Hormonal disturbances

Any condition that affects your hormones, including polycystic ovary syndrome (PCOS), thyroid dysfunction, hyperprolactinemia and others can affect your menstrual cycle phases and, in turn, how light your monthly bleed is. 

“This is kind of a catch-all [term],” Dr. Flanagan says. “Above are only some of the causes of lighter menstrual cycles, but do seek medical attention if you are worried. Typically, a series of blood tests will be performed to rule in or out some of the above-mentioned conditions.”

6. Pregnancy

Many people think that it’s impossible to get your period if you’re pregnant, but that’s not always the case, as Dr. Van Dis explains. 

“The bleeding that can happen during an early pregnancy isn’t really a ‘period,’ but it can match the date when you expect your menstruation,” she says. This is usually caused by implantation bleeding — a light amount of bleeding or spotting that occurs post-pregnancy, around 10 to 14 days after fertilization. It’s seen as “normal” and does not require medical attention. Alternatively, bleeding during pregnancy could be a sign of a miscarriage, an ectopic pregnancy (an unviable pregnancy that involves a fertilized egg growing outside of your uterus), or an anembryonic pregnancy (when a fertilized egg attaches itself to the uterus but doesn’t develop into an embryo).

It’s worth noting here: it’s tricky to tell the difference between implantation bleeding and any of these other conditions, so do seek medical advice if you’re at all worried about bleeding during pregnancy. 

Similarly, if you’ve just given birth, breastfeeding can cause your monthly bleed to be lighter than usual. 

Light periods: The takeaway

You know your body best. “Changes to one cycle are not typically something to be worried about, but if you notice your periods getting further apart, at irregular intervals, or being very light, it’s worth a trip to a health care provider to get checked out,” says Dr. Perez. 

“The easiest way to start dealing with any menstrual issues is by tracking your cycle,” explains Dr. Van Dis. You can keep track of your cycle using Flo, as well as logging any other symptoms you notice. That way, when you see a medical professional, you’ll have plenty of specific and detailed information ready to go that may come in handy for a doctor to know.

It’s important to get to the root cause of your light periods, as it might be an indication of an underlying condition — and have an impact on your day-to-day life, which is no fun. So schedule a checkup. Your doctor should be able to work with you to decide whether further investigation is needed and to help put your mind at ease.