Bleeding from the rectum, or “bum,” during a menstrual period is a common concern. While the presence of blood from the anal area should always be noted and checked by a medical professional, the timing suggests a connection to menstruation. The reproductive and digestive tracts are in close proximity, and the hormonal changes that trigger a period significantly influence bowel function. This co-occurrence means the bleeding is often related to temporary changes in the gastrointestinal system, rather than a direct flow from the uterus itself.
Understanding the Connection Between Menstruation and Rectal Symptoms
The physiological link between the menstrual cycle and changes in bowel habits centers on hormone-like compounds called prostaglandins. These substances are released by the uterine lining to cause the strong muscular contractions of the uterus that result in menstrual cramping. Prostaglandins are not confined to the uterus; they enter the bloodstream and travel to nearby smooth muscle tissue, including the gastrointestinal tract.
When prostaglandins affect the smooth muscles of the intestines, they cause increased motility, speeding up the movement of contents through the bowels. This increased muscular activity can manifest as diarrhea, loose stools, or more frequent bowel movements. The rapid or forceful expulsion of stool can irritate the delicate lining of the anus, leading to minor, temporary bleeding, particularly in individuals prone to existing anal conditions.
Anatomical closeness is another contributing factor. The vagina sits directly in front of the rectum and anal canal, separated by only a small amount of tissue. Due to this proximity, menstrual blood exiting the vagina can smear toward the anal opening, leading a person to mistakenly believe the blood originates internally from the rectum. Hormonal fluctuations, such as the rise and fall of progesterone, can also lead to alternating periods of constipation before the period and diarrhea during it, both of which strain the anal tissues.
Identifying Non-Menstrual Causes of Rectal Bleeding
Most instances of minor rectal bleeding are attributable to localized issues in the anal or rectal area, which are aggravated by the changes that occur during menstruation. Anal fissures are small tears in the thin, moist tissue lining the anus. These tears are frequently caused by passing hard or large stools, or by excessive straining associated with constipation. The pain from a fissure is often described as sharp or burning during and immediately after a bowel movement, with bright red blood appearing as a streak on the stool or toilet paper.
Hemorrhoids are swollen or dilated veins in the rectum or around the anus. These can be internal, where they are less likely to cause pain but may bleed, or external, which can be painful, itchy, and swollen. Hormonal shifts during the menstrual cycle, especially increased progesterone, can cause the pelvic floor muscles to relax, which increases pressure on the anal veins. This can make existing hemorrhoids swell and become more prone to bleeding.
The straining caused by constipation or the irritation from diarrhea—both common period-related bowel changes—can exacerbate hemorrhoids or fissures, making them bleed more prominently during the menstrual week. A less common, though still benign, cause is proctitis, which is inflammation of the rectal lining. While these localized conditions are the most frequent culprits, any rectal bleeding, even if minor, should be investigated to ensure a proper diagnosis and treatment plan.
Distinguishing Minor Bleeding from Warning Signs
When assessing rectal bleeding, the color of the blood is a useful indicator of its source. Bright red blood suggests the bleeding is coming from the lower gastrointestinal tract, such as the anus or rectum, and is generally associated with minor causes like fissures or hemorrhoids. This type of blood often appears as a streak on the outside of the stool or on the toilet paper after wiping.
In contrast, blood that is dark red, maroon, or black and tarry usually indicates bleeding higher up in the digestive tract, such as the colon or stomach, and is more concerning. The darker color results from the blood being partially digested as it travels through the intestines before being passed. Blood that is thoroughly mixed into the stool, rather than just on the surface, may also suggest a higher source of bleeding.
Certain accompanying symptoms are considered red flags that require immediate consultation with a healthcare provider, regardless of the timing in the menstrual cycle. These warning signs necessitate a thorough medical evaluation:
- Passing a significant volume of blood.
- Experiencing dizziness, light-headedness, or fainting, which can indicate substantial blood loss.
- Any persistent change in bowel habits.
- Unexplained weight loss or severe abdominal pain.
- A family history of inflammatory bowel disease or colorectal cancer.
A doctor can perform tests to rule out more serious conditions, such as deeper gastrointestinal issues, or, rarely, deep infiltrating endometriosis of the bowel, ensuring the cause of the bleeding is accurately identified.