Menstruation is when the body sheds the lining of the uterus every month. It’s driven by hormones and is a different experience for everyone, including how long it lasts. The average length of a menstrual cycle is 28 days, but it’s perfectly normal for a cycle to be longer — or shorter — than that.
Periods can last anywhere from a few days to an entire week and have a lighter or heavier flow. If a lighter period is your body’s natural rhythm, it will very likely not have an impact on your overall health or fertility.
“I’m more concerned about periods being too long or too heavy,” says Teresa Hoffman, MD, an ob-gyn at Mercy Medical Center in Baltimore. “I’m not usually concerned about it being too light.” Heavy menstrual bleeding can lead to fatigue and anemia, and it can also be a sign of a serious underlying medical issue.
But if you notice your period is suddenly becoming lighter, that may be a sign that something different is going on with your body.
“A typical menstrual cycle lasts around 21 to 35 days, so anything shorter than this is considered a short cycle,” says Amy Lasky, MD, an obstetrician–gynecologist at Stony Brook Medicine in Lake Grove, New York. That normal range can translate into anywhere between three to seven days of monthly bleeding, and people tally up those days differently. For example, Dr. Hoffman says, some people count the light spotting before or after a period as part of the entire duration, while some don’t.
Factors like age, exercise, and birth control can affect the length of a cycle and explain why there is so much variability.
There are several reasons why a menstrual cycle may suddenly run short, as opposed to a short cycle being your normal rhythm.
Age
Teens and tweens may have short and irregular periods as they enter puberty because their hormone levels, including estrogen, haven't balanced out yet. Older women approaching menopause may also experience irregular or short menstrual periods, because fluctuating hormones can make periods erratic during the last years of fertility.
Birth Control Method
Light menstrual flow can also be a result of the type of contraception you use. “When someone is on a type of hormonal birth control, it is common in the first few months to have [light] bleeding between cycles,” Dr. Lasky says. Examples of hormonal birth control include pills, patches, implants, shots, vaginal rings, and certain types of IUDs.
Early Sign of Pregnancy
Your bleeding may become nonexistent or lighter because of pregnancy (though if it is, you are of course not experiencing a true period), and your healthcare provider will want to rule that out before considering other causes. Another possibility is an ectopic pregnancy, which is when a fertilized egg implants somewhere other than a uterus. Symptoms of this type of pregnancy include a missed period, abnormal vaginal bleeding, and abdominal pain, and they often happen 4 to 12 weeks after the last normal menstrual period.
Polycystic Ovary Syndrome
Polycystic ovary syndrome (PCOS) is a hormonal and metabolic condition that affects roughly 1 in 10 women of childbearing age. One common sign of PCOS is experiencing fewer and irregular periods. It’s possible for someone with PCOS to have fewer than nine periods a year with more than 35 days between them, and others with this condition may experience abnormally heavy periods.
Lifestyle Factors
Disruptions to your regular routine can alter your menstrual cycle duration. Some of those lifestyle factors include:
Remember, a short cycle isn’t typically an issue if that’s your usual monthly pattern. But you may want to consult with your healthcare provider to rule out pregnancy or other health concerns if your period becomes lighter or irregular when it typically isn’t.
“If your menstrual cycle is outside the 21 to 35 day range — particularly if it’s outside that range for more than six months — that’s a good time to talk to your doctor,” Lasky says.
Keep track of your period in a journal or calendar if you’re concerned it has become shorter. You’ll have the most accurate information to share with your gynecologist and be able to easily detect a menstruation pattern that’s not normal for you.
A healthy menstrual cycle can span anywhere from 21 to 35 days, and bleeding can last for three to seven.
Shorter cycles can be caused by your age, birth control method, or lifestyle factors like stress, weight loss, or weight gain.
If the length of your menstrual cycle becomes noticeably shorter, there may be something changing in your body, and you should see a gynecologist.
