Why do I get a chub when I poop? Understanding a physiological quirk

September 21, 2025 •

4 min read

The autonomic nervous system, which controls involuntary body functions, is responsible for both digestion and sexual arousal. It is this shared neurological pathway that explains why a person might sometimes experience an erection when pooping, a phenomenon more common than you might think.

Quick Summary

This sensation is a normal, though rarely discussed, physiological reflex involving the parasympathetic nervous system, increased pelvic blood flow from straining, and potential stimulation of the prostate gland.

Key Points

Normal Physiology: Experiencing an erection during a bowel movement is a normal, harmless physiological response, not a sign of a health issue.
Nervous System Link: Both digestion and erections are controlled by the same parasympathetic nervous system, leading to neurological overlap.
Pressure Increases Blood Flow: The physical act of straining during defecation can temporarily increase blood flow to the pelvic region, causing an erection.
Prostate Stimulation: The proximity of the rectum to the prostate gland means a bowel movement can physically stimulate the prostate, which is rich in nerve endings.
Timing Matters: The sensation can be more likely in the morning due to natural hormonal and nervous system cycles.
Seek Medical Advice if Concerned: You should only be concerned if this is the only way you can get an erection, or if you experience pain or fainting.

The Autonomic Nervous System Connection

Your body operates under the control of two primary divisions of the autonomic nervous system: the sympathetic and parasympathetic systems. The sympathetic nervous system is responsible for the "fight or flight" response, handling stress and energy-intensive activities. Conversely, the parasympathetic nervous system is in charge of "rest and digest" functions, which include digestion, defecation, and, notably, sexual arousal and erectile function. Because both bowel movements and erections are managed by the same system, it is not surprising that there can be some neurological overlap. The body's signals for one function can inadvertently trigger a response in the other, leading to this interesting physiological quirk.

The Role of the Vagus Nerve

One of the most significant components of the parasympathetic nervous system is the vagus nerve, the longest cranial nerve in the body. It acts as a major communication highway, running from the brainstem to various internal organs, including the colon. When you strain to have a bowel movement, particularly when constipated, the increased abdominal pressure can stimulate the vagus nerve. This stimulation can trigger what is known as a vasovagal response, which often causes a drop in heart rate and blood pressure. For some people, this can lead to sensations of lightheadedness or a tingly, relaxed feeling. This same nerve stimulation and subsequent neural response can also contribute to sexual arousal, creating a link between defecation and an erection.

Pelvic Pressure and Blood Flow Dynamics

Another factor is the simple mechanics of a bowel movement. The act of pushing during defecation causes a temporary increase in intra-abdominal and pelvic pressure. This increased pressure can lead to a rise in blood flow to the pelvic region, including the rectum and the penis. The temporary surge of blood to the penis can cause an erection. This mechanism is purely physical and not related to sexual thoughts or arousal. It's a simple, mechanical side effect of concentrated muscular effort in the pelvic area.

Prostate Gland Stimulation

The prostate gland, a walnut-sized gland that is a part of the male reproductive system, is located directly in front of the rectum. It is rich with nerve endings and is a source of pleasure when stimulated directly. During a bowel movement, especially a larger one, the stool passing through the rectum can press against and massage the prostate gland. For some men, this physical stimulation can trigger sexual arousal and lead to a temporary erection. This is one of the most common theories for why this phenomenon occurs.

Comparison of Physiological Causes


Cause	Mechanism	Triggering Factor	Sensation Type
Parasympathetic Crossover	Shared nervous system controls both functions.	Involuntary neurological activity.	Neurological reflex, not necessarily arousal.
Increased Pelvic Pressure	Abdominal straining forces blood to the pelvic region.	Pushing during a bowel movement.	Mechanical, pressure-induced erection.
Prostate Stimulation	Stool in the rectum presses against the prostate gland.	Passage of a bowel movement.	Physical stimulation and potential arousal.

Timing and Associated Factors

This experience might be more likely to occur at specific times. Many men experience "morning wood," a nocturnal penile tumescence, due to hormone fluctuations and the dominance of the parasympathetic nervous system during sleep. If a person has a bowel movement first thing in the morning while already in this heightened state of parasympathetic activity, the chances of experiencing a coincidental erection are higher. It's a matter of timing and a pre-existing physiological state.

When to Consider a Doctor's Visit

For most men, getting an erection during a bowel movement is a harmless and normal occurrence, albeit an unusual one. It is not a sign of any health problems and does not require medical intervention. However, there are a few scenarios where it's worth considering a consultation with a healthcare professional:

If it is the only way you can get an erection. This could indicate an underlying issue with erectile function that warrants investigation.
If you experience pain. Conditions like hemorrhoids, constipation, or anal fissures can cause pain during defecation. Persistent pain should be evaluated by a doctor.
If you experience extreme lightheadedness or fainting (defecation syncope). While rare, excessive straining can lead to fainting and should be discussed with a doctor, especially if it happens regularly.

For more detailed health information, it is always recommended to consult with a medical professional. An excellent resource for general health inquiries is the Cleveland Clinic: https://my.clevelandclinic.org/

Conclusion

In summary, the phenomenon of experiencing an erection during a bowel movement is a combination of neurological and physical factors that are entirely normal. It is primarily driven by the overlapping functions of the parasympathetic nervous system, temporary changes in pelvic blood flow due to pressure, and potential stimulation of the prostate gland. Understanding these biological mechanisms can alleviate any concern or embarrassment, reminding you that it's simply a testament to the complex and sometimes surprising connections within the human body.

Frequently Asked Questions

Yes, it is surprisingly common and considered a normal physiological phenomenon. Many men experience this, though it is not widely discussed due to social discomfort.

Straining to push out a bowel movement increases pressure in the abdomen and pelvis. This pressure temporarily increases blood flow to the genital area, which can physically cause an erection.

For some men, yes. The prostate gland is located close to the rectum, and a bowel movement can press against and stimulate it, which can lead to arousal and an erection due to its nerve-rich nature.

Yes, absolutely. The parasympathetic nervous system manages both digestive functions (like defecation) and sexual functions (like erections), so there's a natural neurological crossover.

Typically, no. It is not dangerous or unhealthy. However, if it is the only time you can achieve an erection, or if you experience pain, it's wise to consult a doctor.

Defecation syncope is fainting while having a bowel movement. This happens in rare cases of extreme straining that overstimulate the vagus nerve, causing a temporary drop in heart rate and blood pressure.

Experiencing this in the morning is common. This is often because men naturally experience erections during sleep and upon waking (a state known as 'morning wood'), and a bowel movement during this time can coincide with this pre-existing state of arousal.