Why is my period blood brown? How to know if it's normal and when to see a doctor

• Brown period blood is normal when it's at the beginning or end of your period, or if you tend to have lighter periods.
• If brown period blood is accompanied by unusual pain, a foul smell, blood clots larger than a quarter, or an abnormally heavy flow, then you should see a doctor.
• If brown blood shows up between your periods, then this could be a sign of polycystic ovarian syndrome, a condition that occurs when your body produces too much testosterone.

Period blood isn't always red – it can range from light pink to dark blackish-brown.

Brown period blood usually isn't a cause for concern, but if it shows up in between your periods or with other symptoms like a foul smell, this may be a sign of a medical issue.

Here's what you need to know about why your period blood is brown and when you need to see a doctor.

Brown period blood can be normal

We usually think of blood as bright red, but "blood becomes darker when it has time to oxidize," says Christine Greves, MD, a gynecologist at the Winnie Palmer Hospital for Women and Babies.

This is because the hemoglobin in your blood turns brown when it's exposed to oxygen – and it can happen when blood stays in your uterus for a long period of time. "It is basically blood that is not as 'fresh,'" Greves says.

This usually isn't any cause for concern. Here are a few normal reasons why you might see brown period blood:

• At the start of your cycle, you may be seeing leftover blood from your last period that stayed in your uterus and appears brown.
• At the end of your cycle, you may see brown blood because the blood has spent longer sitting in your uterus before leaving your body.
• If you tend to have light periods, you are also more likely to see brown blood during your period. This is because a light flow means that blood leaves your body more slowly, giving it more time to oxidize.

There are also a few other non-period related reasons why you may be experiencing brown blood flow:

• You might also see brown blood or discharge after menopause. This is because as your estrogen levels drop, the lining of your uterus and vagina can shed and become thinner.
• Brown blood can appear very early in pregnancy. When a fertilized egg attaches to the lining of your uterus, you may have implantation bleeding. This bleeding is lighter than a typical period and can be brown.
• If you've given birth within the last six weeks, your body will continue to get rid of blood and tissue from your uterus. This flow may appear brown.

When brown period blood may be a cause for concern

When brown blood shows up in between your periods, it can be a sign of an underlying medical condition like polycystic ovarian syndrome (PCOS). PCOS occurs when your body produces too much testosterone, making your ovaries grow larger and develop abnormal growths.

PCOS can also stop your ovaries from releasing eggs. When this happens, your uterus builds up its normal lining, but then doesn't shed it through the usual process of your period. Instead, you may have especially light periods and see bleeding in between periods with old, brown blood or discharge.

In rare cases, brown discharge or blood can be a sign of cervical cancer, but this discharge usually has a foul smell.

Brown blood usually isn't a cause for concern, but Greves advises that you should call your doctor if you have any of these symptoms along with brown blood:

• You're having unusual pain.
• You are bleeding through more than one pad per hour.
• Your blood or discharge has a foul odor.
• Your period is lasting longer than usual.
• You are passing blood clots larger than a quarter.

Insider's takeaway

It's normal to see brown blood during your period, particularly at the beginning or end of your cycle. But if you have abnormal symptoms along with brown blood, or see it in between periods, reach out to your doctor to check if you have an underlying medical issue.

"Just because brown blood is not uncommon, it doesn't mean that it should be ignored," Greves says.

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