Unless you’re trying to get pregnant, a late period can be, well, pretty stressful (or, at the very least, inconvenient). But pregnancy is only one of many reasons your monthly flow might be behind schedule. Sometimes things that seem totally unrelated to your menstrual cycle can mess it up.

Take, for example, getting sick. While you might think one thing (say, the flu) has nothing to do with another (your period), your body’s systems are closely intertwined. So when your immune system is down, it could affect your reproductive system, too.

Here Sherry A. Ross, MD, OB/GYN and author of ‌‌She-ology: The Definitive Guide to Women’s Intimate Health. Period‌, explains why being sick can delay your period (along with other possible causes for a late period), and how to get your cycle back on track.

Can being sick delay your period?

“Your period is often a barometer for your overall health and wellness,” says Dr. Ross. That means if you’re feeling ill, you could see this reflected in your menstrual cycle. Here’s why: when you’re sick, your body’s equilibrium can get out of whack. And this can affect your hormones.

“Significant physical and mental stress can negatively affect your hormonal balance,” says Dr. Ross. This imbalance, in turn, can disrupt ovulation—i.e., when your ovary releases an egg—and affect when (and for how long) you will get your period, she adds.

While a mild cold is less likely to postpone your period, a more significant illness can mess with your menstruation. For example, a “long-lasting flu, with nausea, vomiting, chills, and high fever can delay your period,” says Dr. Ross. And as far as how long the flu can delay your period? This will depend from person to person, but more than likely, only a few days.

“Your period is often a barometer for your overall health and wellness.” —Sherry A. Ross, MD, OB/GYN

Can being sick delay your period when you’re on the pill?

Many people take hormonal birth control pills because it takes the guesswork out of your menstrual cycle—it can literally help predict your period down to the day. But being under the weather can wreak havoc on your regular periods (at least temporarily) whether you use birth control or not.

“During a physically stressful illness, a combination estrogen and progesterone birth control pill can add an extra layer of protection in controlling your period, but there is no guarantee,” says Dr. Ross.

In other words, certain illnesses—like those that cause vomiting and diarrhea—may reduce the pill’s effectiveness because it wasn’t properly absorbed in the gut, per Mount Sinai. This may lead to changes in your period. Likewise, taking certain antibiotics can mess with the pill’s effectiveness, and even cause breakthrough bleeding, per the NHS. In these instances, if you’re not planning to get pregnant, be safe and use a backup birth control method, says Dr. Ross.

Other causes of a delayed period

An illness is only one of many factors that can affect your monthly flow. Here are some of the other most common causes for a delayed period, per the Cleveland Clinic:

1. 1.
   Pregnancy and nursing: When you’re expecting, your body builds up your uterine lining to support and nourish your developing fetus (instead of shedding it, which is what happens when you have your period). Similarly, exclusively breast or chestfeeding can temporarily halt your period, too. That’s because the hormones responsible for making breastmilk inhibit the hormones that control your periods, according to the National Health Service.
2. 2.
   Extreme weight loss, diet, and/or exercise: If you train too hard, lose too much weight too fast, or don’t get enough calories, you may stop menstruating, at least temporarily. This is called secondary amenorrhea. Essentially, this pause in your period is your body’s way of communicating that it doesn’t have what it needs to support a pregnancy.
3. 3.
   Polycystic ovary syndrome (PCOS): PCOS is a hormonal imbalance that interferes with ovulation. If you don’t ovulate, you may have irregular, late, or missing periods.
4. 4.
   Stress: Stress and menstrual changes can go hand in hand. Big-time stressors (think: work stress, major life events, or grief) can affect your hormonal balance, which can ultimately lead to late or absent periods.
5. 5.
   Hormonal birth control: Most contraceptives have hormones like progestin, or a combination or progestin and estrogen, to prevent pregnancy. If you skip your hormone-free week and take your pills continuously, you might miss your period (or simply have some light spotting). Not getting your period is also common—and safe—for people who are using hormonal intrauterine devices (IUD), Nexplanon (arm implants), vaginal rings, continuous patches, and more.
6. 6.
   Thyroid conditions: An issue with your thyroid (the butterfly-shaped gland at the base of your neck) can affect your hormones and cause irregular, delayed, or missing periods. This can occur if your thyroid produces too much or too little hormone.
7. 7.
   Perimenopause: Perimenopause—the transition from your reproductive years to menopause—can cause irregular or late periods (along with other symptoms like hot flashes, insomnia, mood changes, cramping, night sweats, and vaginal dryness).
8. 8.
   Youth: Preteens and teens don’t have a developed hypothalamic-pituitary-ovarian (HPO) axis—i.e., the hormonal system that regulates ovulation and menstrual cycles. When your HPO axis isn’t fully mature, it can produce unpredictable periods (at least until your twenties, when your system settles into a more regular rhythm).

Other possible reasons for irregular or delayed periods include the following, per Dr. Ross:

• Persistent ovarian cysts
• Premature ovarian failure
• Cushing’s disease
• Uncontrolled diabetes
• Congenital adrenal hyperplasia
• Certain medications such as thyroid medicine, steroids, and antipsychotics
• Traveling abroad/across time zones
• Chronic, excessive alcohol use

How to prevent delayed periods from illness

While it might not be totally possible to prevent late periods when you’re sick, you can do a few things to prioritize your health and get your body back on track. Here are Dr. Ross’s tips for supporting your immune system, and, consequently, a healthy hormonal balance:

• Eat a colorful, plant-based diet: Fill up on fruits, vegetables, legumes, whole grains, and lean sources of protein.
• Stay well-hydrated: Aim to get anywhere between 11 and 15 cups of water per day, through drinking and eating water-rich foods, per the National Academies of Sciences, Engineering, and Medicine.
• Exercise regularly: Try to get at least 30 minutes of moderate-intensity exercise per day, according to the Centers for Disease Control and Prevention (CDC).
• Limit alcohol intake: If you do drink alcohol, take stock of how many drinks you have per day/week. Then see where you can cut back or switch to mocktails, instead.
• Manage stress through mindfulness, yoga, and meditation: Find what makes you feel relaxed and incorporate it into your weekly routines.

When to see a doctor about a delayed period

An occasionally late period from stress or the flu is usually no big deal. But if you have late or regular periods more often than not, it could be a sign of an underlying health condition.

If your delayed periods continue for more than two or three months, it’s time to talk to your doctor, says Dr. Ross. She also recommends tracking your period—with either a period tracker app or just on a calendar. By keeping tabs on your monthly cycles, you’ll know right away if something seems off. This information can also be useful to share with your doctor.

FAQ

How much delay in your period is normal?

While some people have pretty regular periods, others experience a little variation when Aunt Flo visits. This is totally normal. In other words, if your period is a day or two late, especially when you’re sick, there’s usually nothing to be alarmed about, says Dr. Ross.

But if it’s been more than 35 days since your last period, or your period is more than three days late (when it normally comes like clockwork), this delay might be an indicator that something’s up, according to the Cleveland Clinic. Again, it’s best to see your doctor to determine whether there’s a problem and rule out any possible medical issues.

Can being sick with COVID-19 delay your period?

It depends on the severity of the infection, says Dr. Ross. For some, COVID-19 is nothing more than a minor, inconvenient cold, while others may have more serious symptoms. Those in the latter group are more likely to have a disruption or delay in their menstrual cycle due to the increased stress on their body.

Can any illnesses cause longer periods?

Sickness and menstrual irregularities can go the other way, too, causing longer periods. Though everyone is different, most people who get a period typically bleed for four to five days and only lose a little bit of period blood (2 to 3 tablespoons), according to the CDC.

But if your period lasts longer than seven days, or you bleed a lot (think: you have to change your pad or tampon every hour), you could be dealing with heavy menses, aka, heavy bleeding.

This type of bleeding can be a sign something’s going on in your body. Prolonged periods are usually caused by certain medical conditions including the following, per the CDC and Mount Sinai:

• Benign growths or tumors on your uterus (like fibroids or polyps)
• Uterine, ovary, or cervical cancer
• Pregnancy-related issues like miscarriage or ectopic pregnancy (when the fetus starts to grow outside the uterus)
• Hormonal imbalances
• Endometriosis and adenomyosis
• Infection of the uterus or cervix
• Bleeding-related disorders, such as von Willebrand disease (VWD)—a blood disorder where blood does not clot properly
• Nonbleeding-related disorders like liver, kidney, or thyroid disease, pelvic inflammatory disease, lupus, diabetes, cirrhosis, and cancer
• Certain drugs (including anticoagulants and anti-inflammatory medications like aspirin) and contraceptives (like birth control pills and IUDs)

If you have excessive bleeding or a period that lasts longer than seven days, it’s important to talk with your doctor who can determine whether an underlying disorder is to blame.

—medically reviewed by Andrea Braden, MD, OB/GYN