Brown period blood is a normal finding and usually does not indicate any health problems, especially if it happens at the beginning or end of a period. However, brown period blood that appears frequently can be a sign of hormonal changes, uterine problems, stress or a sexually transmitted infection.

Brown period blood can also be seen when starting birth control, when birth control is changed, or after taking the morning-after pill is. In these cases, menstruation can also be darker or have a coffee ground texture, although it usually returns to normal by the next cycle. Learn more about what can cause brown vaginal discharge.

If the color of your period blood becomes brown or darker than normal, or if it you have any concerns about how it looks, you should consult your family doctor or gynecologist. They can assess for any abnormalities and initiate treatment as necessary.

Why is my period blood brown?

Dark period blood that is black, brown, or similar to coffee grounds may be caused by:

1. Pregnancy

A small amount of pink, brown or dark red bleeding is common in the first weeks of pregnancy as the embryo attaches to the walls of the uterus.

However, when this bleeding occurs at a later stage of pregnancy or is accompanied by other symptoms such as abdominal pain, shoulder pain, dizziness or excessive fatigue, it may indicate an ectopic pregnancy or miscarriage. You should be assessed immediately if you have any of these symptoms to rule out any problems.

Learn more about what can cause brown discharge during pregnancy.

2. Emotional changes

Some changes in a woman's emotional state, such as increased stress or depression, can affect the structure of the uterus by reducing the thickness of its walls. This change delays shedding of the uterine lining in preparation for menstruation, and blood has more time to become oxidized making it darker in color.

3. Hormonal changes

Hormonal changes, which can happen with thyroid problems or menopause, can cause small amounts of dark period blood. This change is also very common when switching birth control or when recently post-partum women start weaning from breastfeeding.

4. Sexually transmitted infections

Sexually transmitted infections caused by bacteria, such as gonorrhea or chlamydia, cause a more rapid breakdown of menstrual blood, which makes it darker. This type of blood is usually also accompanied by a foul smell, brown discharge before or after menstruation, pelvic pain and a fever above 38º C.

Learn more about the most common STIs and the symptoms they can present with.

5. Endometriosis and other conditions

Endometriosis is the growth of endometrial tissue outside the uterus. This type of problem, or other conditions like adenomyosis, can cause severe pain in the pelvic region and dark discharge, similar to coffee grounds, that can occur both during and between menstruation. Read more about the symptoms of endometriosis and how this condition can present differently from person to person.

In these cases, the period, besides being brown, can also last up to 7 days. In case of suspicion, you should go to the gynecologist for assessment and treatment as necessary (which may include surgery).

6. Post-partum discharge

During the post-partum stage, brown blood is also an expected, normal finding. The uterus takes about 45 days to return to its normal size and bleeding typically happens during this time. This bleeding isn’t exactly menstruation, but it can be dark in color, and may confuse many women.

When to see a doctor

Changes in menstrual bleeding are usually related to normal factors and do not indicate health problems, but you should go to the gynecologist if you have brown period blood other symptoms, such as:

Period lasting more than 7 days
No period for more than 3 months
Vaginal bleeding between periods
Vaginal pain
Fever above 38º C or 100.4º F
Dizziness
Pale skin throughout the body or below the nails.

It is also important to remember that in cases of suspected pregnancy, the appearance of dark bleeding, with clots or in large quantities, is also a reason to see the doctor, because it may be a miscarriage, and a curettage may be necessary to clean the uterus.