Endometriosis can affect a person’s periods in various ways, such as making them longer, heavier, and more painful. Heavy menstrual bleeding due to endometriosis may involve blood clots.

Endometriosis is a condition that causes tissue similar to the uterus lining to grow outside the uterus.

Read on to learn more about how endometriosis can affect a person’s periods, as well as what different colors of period blood can mean.

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There is no research to indicate that endometriosis period blood looks different from typical period blood. However, people with endometriosis may notice that their periods are heavier and last longer.

Endometriosis can also cause a person to have spotting. Spotting is when a person bleeds in small amounts between periods. Blood that occurs due to spotting may be red, pink, or brown.

People with more advanced stages of endometriosis may have ovarian cysts. These cysts, also known as endometriomas or chocolate cysts, contain old blood.

If the endometriomas rupture, they can leak dark brown, bloody fluid into the pelvis. This can cause pain, inflammation, and scarring.

Some people who have endometriosis experience heavy menstrual bleeding. According to the Endometriosis Foundation of America, this can often include blood clots.

The Centers for Disease Control and Prevention (CDC) note that blood clots that are the size of, or bigger than, a quarter can be a sign of heavy bleeding.

A person who has typical periods will generally find that their periods last between 3–7 days.

However, a person with endometriosis may have periods that last more than 7 days. They may also have heavier bleeding than a person without endometriosis.

Heavy bleeding associated with endometriosis may result in a person changing their pad or tampon every 1–2 hours.

In general, a typical menstrual cycle lasts between 21⁠–⁠35 days. A person’s menstrual cycle starts on the first full-flow day of their period and restarts when their next period begins.

If a person has irregular periods, they may find their menstrual cycle is less than 21 days or more than 35 days. The length of their cycle may also vary by 7⁠–9 days each month.

Information from the International Planned Parenthood Federation notes that endometriosis can be a cause of irregular periods.

There is no evidence to suggest that endometriosis stops a person from having periods. However, one of the treatments for endometriosis is preventing periods with hormonal contraceptives.

Endometriosis tissue acts similarly to uterus tissue, which means it bleeds during a person’s period. By preventing periods, hormonal contraceptives can help to reduce pain and bleeding from endometriosis.

This section looks at some of the different colors of period blood and what they might mean.

Learn more about period blood colors here.

Bright red

If a person’s period blood is bright red, it indicates that the blood is fresh. Blood darkens over time, so bright red blood means a person’s period blood is flowing steadily out of the uterus.

The United Kingdom’s National Health Service (NHS) notes that period blood is typically red when at its heaviest. This is generally within the first 2 days of the period starting.


Black period blood can be the result of older blood leaving the uterus. The NHS notes that this may occur on days with lighter bleeding.

Brown or dark red

Brown or dark red period blood may occur during lighter stages of a period.

These colors can occur as the blood oxidizes over time. In this situation, the blood has not yet aged to the point where it becomes black.


A condition called bacterial vaginosis (BV) can cause thin, gray discharge. BV occurs due to a buildup of bacteria inside the vagina.

In addition to gray discharge, BV can also cause:


Pink period blood can occur as a person’s period starts to become lighter.

Typical period blood may have a slight metallic smell due to its iron content.

If a person’s period blood has an unpleasant odor, it may mean they need to change their pad or tampon. Old period blood can gather bacteria, which can cause it to smell.

Foul-smelling discharge can be a symptom of certain infections, such as BV and trichomoniasis, a common type of sexually transmitted infection (STI).

Endometriosis can cause a person to experience gastrointestinal symptoms. This may be a result of endometriosis tissue developing on the bowels.

If a person has endometriosis in their bowels or rectal wall, they may have blood in their stool. They may also experience:

Learn more about endometriosis in the bowels.

Endometriosis tissue can develop in a person’s bladder. If this occurs, a person may experience blood in their urine.

Research from 2015 found that bladder endometriosis can cause:

The researchers note that around 20% of people with bladder endometriosis experience blood when urinating.

Learn more about bladder endometriosis.

A person should contact a doctor if they have any signs of endometriosis or are concerned about period pain or irregularity.

Symptoms of endometriosis include:

When diagnosing endometriosis, a doctor will first ask a person about their symptoms and medical history. The doctor may also perform a pelvic exam and do some imaging tests.

Surgery is currently the only way for healthcare professionals to confirm that a person has endometriosis. The most common surgery used to diagnose endometriosis is laparoscopy.

A laparoscopy involves a surgeon making a small cut in a person’s abdomen. The surgeon then inserts a laparoscope (thin tube with a light and camera) into the incision. This allows the surgeon to look for endometriosis tissue.

Learn more

Learn more about diagnosing endometriosis.

There is currently no cure for endometriosis. However, there are various treatments available to manage symptoms.

Endometriosis treatments include:

If a person has painful periods due to endometriosis, they may find relief from:

  • pain relief
  • hormonal birth control
  • alternative therapies, such as acupuncture and acupressure
  • exercise
  • taking a warm bath
  • using a heating pad or hot water bottle on the abdomen
  • ensuring they get enough rest
  • relaxation techniques, such as meditation or yoga

Although there is no cure for endometriosis, certain treatments can help to manage a person’s symptoms.

Endometriosis patches can regress without treatment in one-third of people with the condition.

Following surgery, endometriosis patches reoccur in 6⁠–67% of people. Pain following treatment reoccurs in 5⁠–59% of people with the condition.

Having endometriosis can reduce a person’s chance of becoming pregnant. It also increases the risk of pregnancy loss and ectopic pregnancy.

A person may be able to manage or reduce heavy bleeding caused by endometriosis. Treatment options they may wish to discuss with a doctor include:

  • NSAIDs
  • hormonal birth control
  • relaxation techniques
  • tranexamic acid, a medication used to help prevent excessive blood loss
  • surgery to remove the womb lining
  • hysterectomy

This section answers some frequently asked questions about endometriosis period blood.

Can endometriosis tissue come out during menstruation?

No, endometriosis tissue does not come out during a person’s period.

Where does endometriosis blood go?

Endometriosis tissue bleeds and sheds in the same way as endometrium tissue. However, the blood and tissue remain trapped inside a person’s abdomen. This can cause inflammation and scarring.

Endometriosis is a condition that causes endometrium tissue to grow outside the uterus. It can affect a person’s period in various ways, such as by causing it to be heavier, longer, and more painful.

Period blood can come in a variety of different colors. A person should contact a doctor if they notice:

  • unusual changes in the color of their period blood
  • changes in the odor of their period blood
  • symptoms of endometriosis
  • foul-smelling or discolored discharge

Although endometriosis has no cure, there are many ways to treat and manage its symptoms.