Regular menstrual periods are a fact of life for most women. But bloody vaginal discharge outside your period can seem alarming.

It can sometimes signal a major problem. Often, however, minor concerns are behind bloody vaginal discharge.

You should call your doctor whenever you have unusual vaginal bleeding. There are many causes, and these are some of the most likely.

Hormone Imbalance

Periods happen when your body sheds the lining of your uterus. When you have a hormone imbalance, your body isn’t getting the signals it needs to do this on schedule. The result may be bloody vaginal discharge between periods.

For teenagers, that may happen when they start getting their periods. Women nearing menopause may also bleed unexpectedly due to shifting hormones.

There’s not much you can do to stop abnormal bleeding due to a hormone imbalance -- unless you’re overweight. Because extra weight can throw your hormones off, losing weight may help prevent discharge with blood.

Pregnancy

You can expect your period to stop when you’re pregnant. But 15%-25% of women have some bleeding during the first trimester.

• Light bleeding may happen 1-2 weeks after the fertilized egg implants in your womb.
• Your cervix may bleed more easily as it gains more blood vessels.
• You may notice spotting after sex, a Pap test, or a pelvic exam.

If you’re pregnant and find more than a little bit of blood, especially after the first trimester, call your doctor right away. This could be a sign of:

• Miscarriage, which usually happens in the first 13 weeks
• Ectopic pregnancy, when the fertilized egg implants outside the uterus
• Preterm labor
• Problems with your cervix
• Problems with your placenta

Birth Control

Birth control pills can do more than prevent pregnancy. Sometimes doctors prescribe them to help a woman have periods that are more regular. But they can also cause abnormal vaginal bleeding. This is especially common with the progestin-only “mini-pill.”

The same is true for women who have an intrauterine device (IUD), a small, plastic device that a doctor inserts into your uterus to prevent pregnancies. IUDs that release hormones help women have less abnormal bleeding. In some cases, they can also cause bloody vaginal discharge outside of normal periods.

There isn’t one type of birth control that’s best for all women. Tell your doctor if you start or continue to have abnormal bleeding with your birth control. You may need to switch to another one.

Menopause and Hormone Replacement Therapy

Menopause is when you permanently stop getting your period, but it doesn’t happen overnight. You may have symptoms for years. A common one is light, irregular bleeding, which might seem like bloody discharge.

There’s another reason why women in the early stages of menopause often have unusual vaginal bleeding. Some of them take hormone replacement therapy (HRT) to control their symptoms. HRT is a common cause of uterine bleeding.

Don’t assume that any blood you see is due to changes in your body as you near menopause -- or any medicine you take. It’s better to play it safe and call your doctor, especially since endometrial and uterine cancer are more common in older women than younger ones.

Thyroid Disease

The thyroid gland makes a hormone that helps control a lot of body functions, from your heart rate to your menstrual cycle. Irregular periods can happen when your body has too much thyroid hormone (hyperthyroidism) or not enough of it (hypothyroidism).

If you have an overactive thyroid, you may also have some of these symptoms of hyperthyroidism:

• Losing weight without trying
• A faster heart rate
• Irregular heartbeat
• A pounding or fluttering heartbeat, called palpitations
• A boost in appetite
• Mood changes, such as feeling anxious or irritable
• Trembling fingers or hands
• Sweating

If an underactive thyroid is causing your bloody discharge, you may also have some of these common symptoms of hypothyroidism:

• Fatigue
• Sensitivity to cold
• Constipation
• Dry skin
• Weight gain
• Puffy face
• Hoarse voice
• Higher cholesterol
• Muscle weakness or aches
• Joint pain, stiffness, or swelling

Thyroid medications or surgery to remove the gland may be treatment options for you, depending on your age, the severity of your condition, and other things you’ll discuss with your doctor.

Polycystic Ovary Syndrome (PCOS)

PCOS is a hormone disorder. It causes tiny, fluid-filled bubbles called cysts to grow in the ovaries. The result can be:

• Periods that are irregular, long, or don’t come often
• Ovaries that don’t work well
• Extra facial and body hair due to higher levels of a male hormone in your body

If you have PCOS, your doctor will work with you to manage its effects on your body. Birth control or progestin therapy can make your periods more regular. There are also medications to help you ovulate and a range of strategies to help control excess hair.

Problems With Your Uterus, Cervix, or Ovaries

Rarely, bloody vaginal discharge is a sign of a more serious problem in your reproductive system, such as:

• Endometriosis (when the lining inside your uterus grows on the outside of it)
• A burst ovarian cyst
• Uterine cancer
• Cervical cancer
• Ovarian cancer

It’s especially important to see a doctor about bloody discharge if you are in menopause, as any vaginal bleeding during this time is a red flag for a serious condition.

Infections

Infections, including sexually transmitted infections (STIs), can cause bloody vaginal discharge. A few of these include:

Vaginitis. This inflammation of the vagina is often caused by three types of infections: yeast, bacterial vaginosis, and trichomoniasis. Vaginitis can cause vaginal itching, discharge, pain when you pee, and light bleeding or spotting between periods. Your doctor can prescribe a pill or cream to treat it.

Chlamydia. In women, this STI can cause bleeding between periods and after sex. You may also have pain when you pee and lower belly pain. Your doctor will treat it with antibiotics.

Pelvic inflammatory disease (PID). This infection of a woman’s reproductive organs can cause no symptoms. Sometimes your doctor only finds it when you have problems getting pregnant or start having chronic pelvic pain. When there are symptoms, they can include irregular bleeding -- between periods and after sex -- as well as bad-smelling discharge and pelvic pain. Antibiotics can treat PID. If you have a serious case, you may need to stay in a hospital while you get treatment. Chlamydia is a common cause of PID, which is one reason it’s so important to treat the STI before it spreads.