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Bodies, hormones, and lifestyles vary so much, it’s pretty tough to know what’s “normal” for your period. But if there’s been a recent change (like your regular 5-day flow has dwindled to 1 day) you might wonder why.

Read on to learn the reasons periods may be shorter than you expect.

According to Planned Parenthood, these are the parameters of a “normal” menstrual cycle:

  • Your entire menstrual cycle (from the first day of your last period to the first day of your next period) can be from 21 to 35 days.
  • A “normal” period lasts 2 to 7 days.
  • Cycles and periods can vary from month to month.
  • An average period is 1 to 6 tablespoons of menstrual fluid.
  • Menstrual fluid can be thin or clumpy, and dark red, brown, or pink.

At a glance: symptoms of a light period

  • period lasts only 1–2 days
  • flow is lighter than “normal”
  • may only be spotting instead of full flow
  • you need fewer pads or tampons than usual
  • PMS or menstrual symptoms (like cramps) are milder

Here are some of the top reasons for barely-there periods.

Vaginal bleeding during pregnancy happens a lot more than you might think. Actually, 15 to 25 percent of women experience bleeding during the first trimester.

Within the first 2 weeks after fertilization, a woman may notice light bleeding or spotting. It’s caused by the fertilized egg implanting in the uterine lining.

Light bleeding may also occur after sex or a pelvic exam due to developing blood vessels in the cervix.

Bleeding can also be a sign of infection, so it’s important to bring it up with your doctor.

Bleeding late in pregnancy can be a sign of labor. Though bleeding in pregnancy isn’t always a problem, cover your bases and get it checked out.

Every stage of your menstrual cycle is controlled by the fluctuation of hormones. Birth control pills contain estrogen and/or progestin to suppress ovulation.

Discontinuing birth control pills can cause irregular periods for up to 6 months. Progestin-only pills can cause bleeding between periods. Anytime you’re prescribed a hormonal medication, ask your doctor how it might impact your period.

Periods usually start around age 12 or 13 and occur monthly until menopause in your early 50s. Many things can impact cycles over the course of 4 decades, but this is how periods typically differ by age:

  • Teens: The first few periods may be very light, or even just spotting, lasting only a few days. It can take up to 3 years for periods to become regular.
  • 20s and 30s: Periods are probably pretty regular, barring any pregnancies or hormone-disrupting illnesses (more on those in a second).
  • 40s: Perimenopause (the 10 years before menopause, or when periods fully stop for 12 straight months) begins, and periods will become irregular. Besides occurring at irregular intervals, they may be lighter or heavier and shorter or longer. Enjoy that roller coaster!

The amount of stress in your life may actually contribute to the problem. In 2015, researchers studied the relationship between stress, hormones, and ovulation.

They found that daily stress interferes with a woman’s menstrual cycle, even if she doesn’t have a known reproductive disorder.

A 2018 study found that among a group of students, those with high stress were 2 to 4 times more likely to experience missed periods, painful periods, or PMS.

Disordered eating, excessive exercise, and weight fluctuation can impact hormones and cause periods to change or disappear altogether. For example:

  • According to the Mayo Clinic, if body weight drops 10 percent below “normal” (good luck defining that), hormones stop ovulation and periods. You may have heard of this happening to women with eating disorders like anorexia and bulimia.
  • A 2014 study found that binge eating is also associated with menstrual dysfunction.
  • Intense or excessive exercise — either as part of eating disorder behavior or athletic training — can also cause periods to diminish or disappear. According to the Office on Women’s Health, this can happen to women who have not exercised much and suddenly start an intense exercise program.

The thyroid produces hormones, like Thyroxine (T4), Triiodothyronine (T3), and Calcitonin, which regulate metabolism and growth.

Thyroid disorders associated with over- or under-production of thyroid hormones can cause these disruptions to the menstrual cycle:

  • early or late puberty
  • very light or heavy periods
  • irregular cycles
  • amenorrhea (no periods)
  • early onset of menopause

One symptom of Polycystic Ovary Syndrome (PCOS) is increased androgens, which can cause irregular or missed periods. It’s unknown what causes PCOS, but irregular menstruation can be one of the first clues you have it.

Other symptoms of PCOS include

  • weight gain
  • excessive body hair
  • loss of head hair
  • acne
  • insulin resistance
  • ovaries that are covered in cysts (detectable by ultrasound)

Another type of ovarian cyst is a single cherry-sized lump that can be filled with fluid or tissue. Besides causing spotting between periods or causing periods to be heavy or irregular, cysts can cause these symptoms:

  • pelvic pain
  • abdominal swelling
  • a feeling of fullness and pressure
  • pain when urinating
  • constipation

Pelvic inflammatory disease is a bacterial infection. You may catch it through sexual contact, gynecological procedures, childbirth, or miscarriage if bacteria enters the vagina and spreads through the reproductive tract.

Besides irregular periods, symptoms may include:

  • heavy vaginal discharge
  • unpleasant odor
  • pelvic and abdominal pain
  • fever
  • nausea
  • vomiting
  • diarrhea

  • Premature ovarian insufficiency is when women under the age of 40 stop having periods, similar to menopause. It can be due to cancer treatment, family history, or chromosomal abnormalities.
  • Cervical stenosis is the partial or complete closure of the cervix. Menstrual fluid and or pus may back up into the abdomen or leak from the vagina.
  • Asherman’s syndrome describes adhesions in the uterus that are associated with infertility and short or light periods. Adhesions can form due to curettage after a recent pregnancy, hysteroscopic surgery, uterine artery embolization, or uterine tuberculosis.

When a fertilized egg implants somewhere other than in the uterus (like in a fallopian tube or elsewhere in the abdominal cavity) it’s called an ectopic pregnancy.

Ectopic pregnancies aren’t viable and may cause the fallopian tube to rupture as they grow. They can cause vaginal bleeding, internal bleeding, weakness, pain in the abdomen or shoulder, shock, and even death.

Miscarriage (pregnancy loss before the 20th week) occurs in 10 to 20 percent of known pregnancies.

Many miscarriages occur before a woman knows she is pregnant and are often mistaken for a normal period. Signs of miscarriage are spotting or bleeding, and pain and cramping in the abdomen or lower back.

While breastfeeding, you produce a hormone called prolactin, which suppresses ovulation and periods.

Depending on how often and how long you breastfeed, your period may not return for several months to a year after childbirth. Periods can be irregular or short and light as long as you’re still breastfeeding.

If your period has become unpredictable or you suspect you have one of the issues mentioned above, check in with your doctor. Planned Parenthood points out that something may be amiss if you experience any of the following:

  • You had unprotected sex and missed your period.
  • You have a very heavy flow (changing pads or tampons more than once per hour).
  • Your period lasts longer than 7 days.
  • You’re light-headed, dizzy, or your pulse is racing.
  • You’ve never had a period by the age of 16.
  • You have severe pain before or during your period.
  • You have unusual bleeding between periods.
  • You feel sick or get a fever when using a tampon.
  • Your periods disrupt normal day-to-day activities.
  • Your periods stop or suddenly become irregular.
  • Your periods come more often than every 21 days or less often than every 45 days.

When it comes to periods, you can expect the unexpected. You get about 40 years to try to figure them out!

But if your period only lasts a day or 2, or is so light you think your seeing spots, consider one of these causes. Many are treatable or may just fall within the range of your “normal” for now.