Menstrual fluid is the discharge of blood and tissue from the uterus that occurs when a pregnancy does not. This process is a regular part of the menstrual cycle, driven by hormones. These hormones prepare the uterine lining for a potential pregnancy, and when one doesn’t occur, this lining is shed.
The Composition of Menstrual Fluid
Menstrual fluid is a complex biological substance, not just blood. Only about half of the fluid is blood, which itself contains plasma components like iron. The reddish-brown color is slightly darker than the blood circulating in veins.
A significant portion of menstrual fluid is the degenerated inner lining of the uterus, known as the endometrium. Throughout the menstrual cycle, hormones prompt this lining to thicken in preparation for a fertilized egg. If pregnancy does not happen, falling hormone levels trigger the shedding of this tissue and its associated blood vessels.
The fluid also contains mucus from the cervix and various vaginal secretions. Together, these elements—blood, endometrial tissue, and other fluids—create the substance discharged during menstruation. The total volume shed during an average period is about 35 milliliters, though a range of 10 to 80 milliliters is considered normal.
Decoding Color and Consistency
The color of menstrual fluid can change throughout a period and is related to the rate of flow. A bright red color typically indicates fresh blood and a steady flow, as the fluid is passing from the uterus quickly. This color is common during heavier days when uterine contractions, which can feel like cramps, lead to a more rapid expulsion.
As the flow slows, the color may darken to a deep red, brown, or even black. This is because the blood has had more time to oxidize, a chemical reaction with oxygen, before it leaves the body. This older blood is often seen at the beginning or end of a period. A pink hue can also occur when blood mixes with cervical fluid during a light flow.
The consistency of menstrual fluid also varies, from thin and watery to thick and gooey. A thinner consistency is often associated with a lighter flow, while a thicker consistency is common toward the end of a period. The presence of small blood clots is normal and happens when the body’s anticoagulants can’t keep up with a heavy flow. However, regularly passing clots larger than a quarter may be a reason to speak with a healthcare provider.
Understanding Menstrual Odor
A slight odor from menstrual fluid is normal and results from its unique components. The blood itself has a metallic smell due to its iron content, which can become more noticeable when the fluid is exposed to air. The natural bacteria that live in the vagina also interact with the menstrual fluid, contributing to its scent.
Hormonal shifts during the menstrual cycle can affect the vagina’s pH level, which influences the bacterial environment and the resulting odor. Increased sweat production in the genital area can also mix with menstrual fluid, creating a scent similar to body odor. Proper hygiene, like regularly changing menstrual products, helps manage this by reducing the time bacteria have to multiply.
A significant change in odor, however, can signal an underlying issue. A strong, “fishy” smell is often associated with bacterial vaginosis, an infection caused by an overgrowth of bacteria. A foul smell could indicate a forgotten tampon. If you notice a persistent and unusual odor, especially if accompanied by other symptoms like itching or irritation, it is advisable to consult a healthcare professional.