7 reasons why your period blood is brown

Noticing brown blood during your period can be surprising, especially if you are used to seeing bright red menstrual flow. While it can sometimes indicate an underlying health concern, in most cases, brown period blood is perfectly normal and simply part of the natural menstrual process.

To understand why period blood changes colour, it helps to know that menstrual blood is not just blood — it’s a mixture of blood, vaginal secretions, and the lining of the uterus (endometrium) that is shed each month. Fresh blood is usually bright red because it contains oxygen-rich haemoglobin. However, the longer it remains inside the body before being expelled, the more time it has to oxidise, which turns it darker, often brown or even almost black.

Here are the main reasons you might see brown blood, explained in detail.

Why Your Period Blood Is Brown

1. Older Blood Being Expelled

The most common reason for brown menstrual blood is simply that it’s older blood leaving the body. This happens because menstrual blood that remains in the uterus or vaginal canal for a longer period of time undergoes oxidation. Oxygen reacts with the haemoglobin in the blood, changing its colour from bright red to dark brown.

You’ll often notice this towards the end of your period when your flow is lighter and the blood moves more slowly, or at the very start of your cycle when the uterus is expelling residual blood from the previous month. This is entirely normal and is just your body completing its natural shedding process.

2. The Start or End of Your Period

Brown blood is especially common during the first and last days of menstruation. At the beginning of your period, the flow may start off slow as the cervix begins to open, so the initial blood takes longer to exit the body. This gives it time to oxidise, resulting in a brownish shade.

Similarly, at the end of your cycle, your uterus is clearing out the last bits of endometrial lining, and the lighter flow means blood takes longer to pass through the vaginal canal. By the time it appears on your pad, tampon, or menstrual cup, it is often dark brown.

3. Spotting Between Periods

Brown discharge can sometimes occur between periods, a phenomenon known as spotting. This may happen due to hormonal fluctuations, stress, starting or stopping hormonal birth control, or ovulation.

In the case of ovulation spotting, a small amount of bleeding can occur when the egg is released, and because it’s minimal, the blood may oxidise before leaving the body, resulting in brown discharge. While occasional spotting is usually harmless, persistent or heavy spotting between periods should be discussed with a healthcare professional to rule out other causes.

4. Implantation Bleeding in Early Pregnancy

For women who are pregnant, brown blood can sometimes appear due to implantation bleeding. This happens when a fertilised egg attaches to the uterine lining, typically occurring 6–12 days after conception. The bleeding is usually light, ranging from pink to brown, and is not the same as a period.

The brown colour indicates that the bleeding is light and not fresh. However, if you suspect pregnancy, it’s important to take a test and seek medical advice, particularly if the bleeding is accompanied by pain or unusual symptoms.

5. Post-Menstrual Residue

Even after your main menstrual flow ends, small amounts of blood can remain in the uterus or vaginal canal. Over the next day or two, this blood may slowly make its way out, appearing brown as it has already been exposed to oxygen.

This is simply your body completing the final phase of menstruation. Wearing a panty liner for an extra day or two after your period can help you stay comfortable and prevent staining.

6. Possible Underlying Medical Conditions

Although brown period blood is usually harmless, it can sometimes be linked to underlying gynaecological conditions. Examples include:

Polycystic Ovary Syndrome (PCOS): Can cause irregular ovulation and prolonged build-up of the uterine lining, leading to spotting or brown discharge.

Pelvic Inflammatory Disease (PID): A bacterial infection of the reproductive organs that can cause abnormal discharge, sometimes brown in colour, accompanied by pelvic pain.

Endometriosis: A condition where uterine lining tissue grows outside the uterus, often causing painful and irregular bleeding.

Fibroids or Polyps: Non-cancerous growths that can alter menstrual bleeding patterns.

If brown blood is accompanied by severe cramping, foul-smelling discharge, fever, or very heavy bleeding, it’s advisable to seek medical attention promptly.7. When to See a DoctorMost cases of brown period blood are nothing to worry about, but there are situations where it’s important to get checked. You should see a healthcare provider if:

The brown blood appears regularly outside your normal menstrual cycle.

You experience strong odour, unusual pain, or fever alongside the bleeding.

You have irregular cycles, missed periods, or sudden changes in your menstrual pattern.

Early medical evaluation can help detect and treat any underlying problems while preventing potential complications.Brown period blood is often just older blood that has taken longer to leave the body, particularly at the start or end of your period. While it can occasionally point to health concerns, in most cases it’s a normal part of the menstrual cycle.By paying attention to changes in your cycle and understanding what’s normal for your body, you can better protect your reproductive health. If you ever feel unsure, it’s always wise to seek advice from a qualified medical professiona