10 Things That Can Throw Off Your Period

Here are reasons why your period is erratic or missing altogether—and what to do about it.

Wouldn't it be great if you could circle a date on your calendar and have your period show up then? Unfortunately, a slight variation is typical.

"The average cycle is 28 days—that's 28 days between the first day of one period and the first day of your next period—but anywhere in between 24 and 31 days is considered normal," said Veronica Lerner, MD, Director of Simulation in the Department of Obstetrics and Gynecology at Lenox Hill Hospital. "Still, a highly irregular period is usually a sign that something else isn't right in your body."

What Can Throw Off Your Period?

Take note of these 10 things that could be affecting your menstrual cycle, and see a healthcare provider if anything seems too far off.

Exercising Rigorously

Have you heard of marathon runners losing their periods? It's not a myth: Frequent rigorous exercise puts stress on your body. This stress tells your brain to stop producing reproductive hormones.

The reason why? "Since you can't nourish a baby under extreme stress, your body temporarily shuts down the production of fertility hormones," explained Dr. Lerner.

There's a medical name for when this happens: "It's a condition called amenorrhea, and it can compromise your bone density long-term," said Dr. Lerner. Amenorrhea can result in a decrease in bone density that may not be reversible.

More About Ameorrhea

Amenorrhea is the absence of a period often caused by stress, weight loss, or frequent exercise. Other symptoms that may be associated with amenorrhea depend on the cause, and can include:

  • Changes in eyesight
  • Extra facial hair
  • Hair loss
  • Headache
  • Lack of breast development
  • Milky breast discharge

Weight Changes

Estrogen is produced mainly from adipose tissue (the tissue that makes up fat) after menopause. However, at any time in a person's life, any extra fat can make estrogen.

This means that when levels of fat in the body increase, estrogen levels also increase. As a result, the extra estrogen affects your menstrual cycle, leading to heavy periods and missed or irregular ones.

"Excess fat cells result in elevated estrogen levels, which can ultimately stop your ovaries from releasing an egg," said Dr. Lerner.

Too much estrogen for an extended period can also increase your risk of breast and endometrial cancer. However, going on the pill may help. Oral contraceptives have been associated with lowering the risk of developing endometrial cancer.

Additionally, if you lose weight too quickly, this may lead to irregular periods as well. In terms of estrogen, your body has the opposite reaction when you lose a lot of weight. It doesn't produce enough estrogen.

"And you need adequate levels of estrogen to build your uterine lining and have a period," said Holly Puritz, MD, medical director of ob-gyn services at Sentara Leigh Hospital. "You're more likely to notice a difference if you've lost a significant amount of weight in a short period of time."

Feeling Stressed Out

Feelings of stress can delay your period. Research has shown that people experiencing high levels of stress were also experiencing irregular periods.

When stress affects the timing of a period, it can affect fertility too. "Evolutionarily speaking, times of high stress aren't conducive to bringing a baby into the world, and a regular cycle is designed to do just that," said Dr. Puritz. That's why those who are stressed out may have a more challenging time trying to conceive or have a healthy pregnancy.

Beyond irregular periods, stress can also affect your menstrual cycle in other ways. For example, individuals under high stress may experience more painful periods and changes in how long their cycles are.

Fluctuating Hormones

Issues with the thyroid—a gland in your neck—can affect the regularity of your period.

Thyroid hormones are responsible for your body's energy control and affect many organs. But when thyroid hormone levels are up or down, your body functioning can change—including in relation to your menstrual cycle.

For those with an overactive thyroid gland—meaning they produce too much thyroid hormone—their periods tend to be shorter and occur more frequently. The opposite is true for those who don't make enough thyroid hormone and have an underactive thyroid. Their periods tend to be less frequent.

But hormones don't act on their own. "All hormones circulate throughout your bloodstream, so they're all connected, even if they're produced in different glands," said Dr. Puritz.

Exposure to Pesticides

Pesticides can be associated with irregular periods, according to a Journal of Occupational & Environmental Medicine study.

Participants in the study had been exposed to pesticides from working and/or living on farmland. Most participants were exposed to endocrine-disrupting chemical pesticides, a pesticide known to cause menstrual irregularities. Participants reported irregularities in the length of their cycle as well as the absence of their period for more than 90 days.

Some classes of chemicals can bind to receptors (molecules on the surface of a cell) for estrogen in the body. As a result, they can copy how estrogen functions in the body. "Pesticides mimic hormones," Dr. Puritz said. "They compete with and block the hormones in your body, making it difficult for your endocrine system to function properly."

But Dr. Puritz suggested limiting your exposure any way you can: "Even choosing organic food at the supermarket helps."


If you choose to breastfeed consistently, you may find that your period doesn't come back right away. This is known as lactational amenorrhea.

Basically, lactational amenorrhea happens after a person gives birth and increases the time it takes for a person to get pregnant again. For that reason, some individuals use it as a birth control method.

More About Lactational Amenorrhea

Using the lactational amenorrhea method (LAM) is meant to be temporary. If someone wants to use LAM as contraception, three conditions must be met to ensure that LAM is safe and effective:

  1. Amenorrhea after giving birth
  2. Breastfeeding full-time or nearly full-time (no more than 4-6 hours between feedings)
  3. Breastfeeding for 6 months after giving birth

However, if you are not using LAM and your period has not resumed after giving birth, consult a healthcare provider to determine what might be causing a delay in your period.

Your Age

Your period may not get regular until your 20s. However, as you approach menopause, periods may become irregular again.

But while you probably expect your period to become less frequent as you approach menopause, it can throw surprises at you. For example, your period may stop for a few months and then return out of nowhere.

Also, thanks to shifts in your hormones, your cycle gets shorter before it gets longer, explained Samantha Butts, MD, associate professor of obstetrics and gynecology at Penn State College of Medicine.

"Then, at a certain point, the number of eggs in your ovaries declines such that your periods are infrequent," said Dr. Butts. That means you'll need to put up with more frequent periods before you can start saying goodbye for good.

Sleeping Poorly

Skimping on sleep can make you feel off, but subpar slumber patterns can throw off your cycle, too. What's more, sleep quality can get worse for individuals who experience premenstrual symptoms.

"Shifting your body clock affects your reproductive hormones, which influence ovulation and menstruation," said Fiona Baker, Ph.D., program director of SRI International's Human Sleep Research Laboratory.

One study analyzed data from 579 participants concerning their menstrual cycles and how regularity was related to sleep duration, quality, and fatigue. The researchers found that heavier bleeding and irregular periods were related to:

  • Sleeping for a shorter time
  • Worse sleep
  • Fatigue
  • Stress
  • Depression

Traveling Across Time Zones

Estrogen levels change throughout your period. But there is an inverse relationship between estrogen and melatonin, meaning that melatonin levels are down when estrogen levels are up, and vice versa.

Your brain produces melatonin to signal your body that it's time to go to bed. But when you travel to another time zone, your body releases melatonin as if you're still at home, even if it's broad daylight in your new location.

To adjust to the new schedule, your body suppresses the hormone until it's dark again. These fluctuations aren't good for your flow: "It's probably not a big deal if you're traveling once in a while, but these adjustments may throw off your cycle if they're happening regularly," said Dr. Baker.

Certain Health Conditions

You may also experience irregular periods if you have different health conditions. These conditions may include:

  • Eating disorders (including anorexia nervosa, bulimia nervosa, and binge eating disorder)
  • Pelvic inflammatory disease (PID)
  • Polycystic ovary syndrome (PCOS)
  • Primary ovarian insufficiency (POI)
  • Uncontrolled diabetes

Depending on the health conditions, you might experience irregular periods, such as infections of reproductive organs (like with PID) or hormonal imbalances (like with PCOS).

Looking for support?

If you or a loved one are coping with an eating disorder, contact the National Eating Disorders Association (NEDA) Helpline for support at 1-800-931-2237. For more mental health resources, see our National Helpline Database.

If this is an emergency call:


What Might Help Regulate Your Period?

Despite all the possible causes of irregular periods, there are things that may be able to help you regulate your period.

Hormonal Birth Control

Oral contraceptives are often used to regulate periods. "Many people go on birth control pills to make their periods regular," said Dr. Lerner. "But it takes your body a few months to adjust."

The pill typically contains two hormones: estrogen and progestin. These hormones prevent the ovaries from releasing an egg. "The pill stabilizes the lining of your uterus, but the lining needs a steady supply of hormones in order to stay put," said Dr. Puritz.

Other types of contraception, like intrauterine devices and implants, can also be used to regulate periods.

Overall Health Management

Taking care of your health by making lifestyle changes may play a role in regulating your periods.

Part of maintaining a regular menstrual cycle is ensuring that you have a healthy body weight. Eating healthy foods and getting physically active are the main ways to manage weight.

Of note, what's considered a healthy weight will differ from person to person. But a healthcare provider can help you determine what that weight should be in your case.

Additionally, make sure that you get quality sleep, which can look like getting enough sleep and having a consistent sleep schedule. Engaging in stress reduction techniques like reading a book or doing yoga can also be helpful.

When To See a Healthcare Provider

It's normal for your cycle to be a couple of days off. However, you'll want to see a healthcare provider if :

  • Your period is consistently late
  • Your period is early by more than one week
  • You get irregular periods when you usually have regular ones

A Quick Review

Many things can cause your period to be delayed or irregular. Some causes include health conditions, breastfeeding, and weight changes. Hormonal birth control and managing your health can help regulate your menstrual cycle. But if you are experiencing irregularities in your menstrual cycle, consult a healthcare provider.

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