The color of menstrual blood can vary from bright red to dark brown, black, and even orange or grayish—and each shade has a meaning. Some changes are natural, some indicate hormonal changes, and some can indicate medical conditions that require attention.
In this article, we will dive deeper into the scientific explanations, understand what the different shades may indicate, and when it is worth seeking medical attention.
Why does the color of blood change during menstruation?
The color of menstrual blood is directly related to the health of the reproductive system and what is happening inside the uterus.[1] A normal menstrual cycle lasts an average of 28 days, with the bleeding itself lasting between 3 and 5 days, during which the color may change – which is completely normal.[2]
The main cause of color changes is a process called oxidation . When fresh blood—which contains hemoglobin, an iron-rich protein—is exposed to oxygen, the iron in it oxidizes and the color changes from bright red to darker shades such as brown and black[3].
The longer the blood stays in the uterus before it comes out, the darker it is.
Additionally, it is important to know that menstrual fluid is not just blood – but a mixture of endometrial cells, immune cells, proteins, and even unique microbial markers – which also makes it an important research tool in various diseases[4][1].
So what does each color mean?
1. Dark brown or black
It usually appears at the beginning or end of bleeding, when blood flow is slower. It is old blood that has undergone prolonged oxidation in the uterus – and therefore its color is darker[5].
In Chinese medicine, blood color is considered an indication of various internal conditions in the body – but the connection between blood color and overall health is still being studied and requires further scientific confirmation[2].
2. Bright red to dark red
A common color during heavy bleeding, when the blood is fresh and flowing quickly, and therefore has not had time to become oxygenated[5].
When the flow weakens, the blood accumulates, oxidizes, and darkens.
An interesting study conducted among rural women in China found a link between blood color and fertility: women who reported bright red blood experienced lower pregnancy rates than women with other colors – raising interest in possible links between blood color and reproductive health[2].
3. Pink
Pinkish blood usually appears at the beginning or end of the period, when the amount is small and the blood mixes with cervical fluids[5].
In some cases, this shade can indicate low hemoglobin levels – and sometimes anemia[2][3].
Hemoglobin levels vary throughout the month, sometimes decreasing during menstruation and the follicular phase of the cycle – which can affect the color of the blood[3].
4. Orange
Orange-colored blood appears when blood mixes with vaginal discharge – but if there is also an unusual odor, itching, or pain – it may be an infection and you should seek medical attention[5].
Studies show that menstrual fluid may contain biomarkers for various infections, making it a possible diagnostic tool in the near future[4][1].
5. Gray or grayish-white
An abnormal color that requires immediate medical attention. This shade may indicate an infection such as bacterial vaginosis or trichomoniasis[5].
If you see gray discharge, especially if it is accompanied by an unpleasant odor or pain – don't wait.
Here too, studies indicate the potential of menstrual fluid for diagnosing infections in the reproductive system non-invasively, using analysis of the fluid's composition[4][1].
When should you see a doctor?
Changes in blood color are usually normal, but there are some symptoms that require attention:
- Grayish or grayish-white discharge, especially if there is an unusual odor [5]
- Orange discharge with itching, burning, or pain [5]
- Extremely heavy bleeding – if you change protection every hour
- Severe pain that disrupts daily routine
- Sudden and unusual changes in your menstrual cycle
Science now recognizes menstrual fluid as a powerful diagnostic tool – from hormonal imbalances to chronic diseases like diabetes, through conditions like endometriosis, chlamydia, and even cervical cancer[4][1].
In conclusion
The color of your menstrual blood has a lot to say about your body.
Usually, the shades change according to the phases of the cycle, which is completely natural. But when something feels unusual, it's worth listening to your intuition and checking.
The research is only getting deeper, and it seems that in the future we will be able to understand much more about women's health through a simple analysis of menstrual fluid.
Remember – everyone is different. What is considered “normal” for someone else – may not necessarily be right for you. If something is bothering you – see a doctor who can provide a personalized response.
