Brown blood is almost always old blood. When blood sits in your body longer than usual before leaving, the iron in it reacts with oxygen, the same basic chemistry as rusting metal. This changes the color from bright red to dark brown. It’s one of the most common things people notice about their periods, but it can also show up in other contexts like wounds, urine, or postpartum recovery.
Why Blood Turns Brown
Fresh blood is red because of hemoglobin, the protein in red blood cells that carries oxygen. Hemoglobin contains iron, and that iron starts in a state that binds oxygen easily and reflects red light. Over time, the iron oxidizes, shifting to a form that can no longer carry oxygen. This oxidized version of hemoglobin is called methemoglobin, and it appears brown. The process is essentially the same thing that happens when a piece of iron rusts in open air.
The speed of this color change depends on how long blood is exposed to oxygen and how slowly it moves. Blood that flows quickly out of the body stays red. Blood that pools, sits in tissue, or trickles out slowly has more time to oxidize and turns brown before you ever see it.
Brown Period Blood
The most common reason people notice brown blood is at the beginning or end of a menstrual period. At these points in your cycle, blood flow is lightest, so the uterine lining sheds more slowly. Instead of flowing out quickly, small amounts of blood linger in the uterus or vaginal canal long enough to oxidize. By the time it reaches your pad or underwear, it’s turned brown or dark brown.
This is completely normal. You might see a day or two of brown spotting before your period picks up to its usual red flow, and then another stretch of brown discharge as it tapers off. The brown color tells you nothing alarming. It simply means the blood took a slower route out.
Implantation Bleeding in Early Pregnancy
Brown or dark brown spotting can also be an early sign of pregnancy. When a fertilized egg attaches to the uterine lining, it can cause light bleeding known as implantation bleeding. This typically happens about seven to ten days after ovulation, which means it can show up right around the time you’d expect your period, making it easy to confuse the two.
There are a few key differences. Implantation bleeding is usually brown, dark brown, or pink rather than the bright red of a normal period. It’s also much lighter, often just spotting rather than a flow, and it lasts anywhere from a few hours to a couple of days. A regular period typically lasts longer and gets heavier before tapering off. If you notice very light brown spotting around the time of your expected period and it stops quickly, a pregnancy test a few days later can clarify things.
Postpartum Discharge
After giving birth, your uterus sheds the extra blood, tissue, and fluid it built up over nine months of pregnancy. This discharge, called lochia, changes color as healing progresses. The first few days are typically heavy and red. Starting around day four through day twelve, the discharge shifts to a pinkish-brown color and becomes less bloody-looking. This second phase is your body continuing to clear out old material as the uterus shrinks back to its pre-pregnancy size.
Brown postpartum discharge during this window is a normal part of recovery. It gradually lightens to a yellowish or white color over the following weeks.
Infections That Change Discharge Color
Sometimes brown discharge isn’t just old blood. Certain vaginal infections can cause unusual discharge that may include brown tones, especially if there’s irritation or minor bleeding involved.
- Bacterial vaginosis produces grayish, foamy discharge with a noticeable fishy smell. If it mixes with small amounts of blood from irritated tissue, the result can look brownish.
- Trichomoniasis causes frothy, yellow-green discharge that smells bad and may have visible spots of blood in it.
- Yeast infections typically produce thick, white, odorless discharge and are less likely to cause brown coloring.
The distinguishing factor with infections is that the brown discharge usually comes with other symptoms: odor, itching, burning, or an unusual texture. Brown blood on its own, without these additional signs, is far more likely to be normal oxidized blood.
Polyps and Structural Causes
Uterine or cervical polyps are small, benign growths that can cause irregular brown spotting. Polyps dangle from small stalks inside the uterus or cervical canal, and as surrounding tissue rubs against them, tiny blood vessels on their surface break open. The bleeding is usually light enough that the blood oxidizes before leaving the body, which is why some people notice a few days of brown spotting after an otherwise normal period.
Uterine fibroids can cause a similar pattern. These noncancerous growths in the uterine wall can disrupt normal blood flow during your period, trapping small amounts of blood that shed later as brown discharge. If you consistently notice brown spotting between periods or have periods that seem to drag on with days of brown blood, polyps or fibroids are worth investigating with your doctor through an ultrasound.
Brown Blood From Wounds or Cuts
Outside of the reproductive system, brown blood on a bandage or around a healing wound is also just oxidation at work. When blood seeps slowly from a shallow cut or scrape, it dries and darkens as the iron in hemoglobin reacts with air. A scab itself is essentially a patch of fully oxidized, dried blood. This is normal healing. The only time wound-related brown blood warrants attention is if the area around it becomes increasingly red, swollen, warm, or starts producing pus, which could indicate infection.
Brown or Tea-Colored Urine
If the brown blood you’re seeing is in your urine, that’s a different situation. Blood in urine can appear pink, red, or cola-colored depending on the amount and how long it’s been sitting in the bladder. Urinary tract infections are one of the most common causes. Bacteria enter the urethra and multiply in the bladder, causing inflammation and bleeding that tints urine brown or reddish-brown.
Less commonly, tea-colored or brown urine can signal kidney problems or severe muscle breakdown (a condition where damaged muscle fibers release their contents into the bloodstream, which the kidneys then filter out). Unlike brown menstrual blood, brown urine is not something to wait on. It typically needs evaluation, especially if it comes with pain, fever, or happened after intense physical exertion.