What Happens When You Hold In a Fart?
Social situations have long compelled humans to clench, tighten, and strategically postpone the inevitable. But what actually happens to a fart you refuse to release? The short answer is: it doesn't disappear. It waits. Sometimes patiently, sometimes not. The physiology of held gas is more interesting — and more consequential — than most people realize.
What Holding In a Fart Actually Means
Voluntary suppression of flatulence involves consciously contracting the external anal sphincter — a striated muscle under voluntary control — to prevent the passage of gas. The internal anal sphincter, which is smooth muscle and involuntary, relaxes during rectal distension to allow passage, but the external sphincter can override this reflex for a limited time. Meanwhile, the gas continues to accumulate in the rectum and sigmoid colon, causing increasing intrarectal pressure. The discomfort associated with holding in gas is primarily mechanical: the stretching of the colonic wall and the pressure on surrounding structures, including the bladder and lower back musculature.
Gas Reabsorption: The Body's Backup Plan
When gas is retained, the body does partially reabsorb some components through the colonic mucosa. Carbon dioxide is reabsorbed most readily; hydrogen and methane are absorbed to a lesser degree. However, this process is too slow to handle the full volume of gas in any reasonable timeframe. A significant amount of retained gas simply redistributes: it migrates back into the proximal colon, contributing to bloating and that characteristic 'full' sensation. Bacterial fermentation continues unabated during this time, often producing additional gas and compounding the problem. The net effect is that retention typically delays rather than eliminates passage.
The Gas Doesn't Disappear — It Escapes Later
Retained intestinal gas must eventually find an exit. The two primary routes are the anus — inevitably, at some later point — and, for gas that has been reabsorbed, the lungs via the bloodstream. Small amounts of hydrogen and methane absorbed across the colonic mucosa enter the portal circulation, are processed by the liver, and are eventually exhaled. This is why breath hydrogen tests are used as a clinical tool to measure intestinal fermentation. Gases held during waking hours commonly emerge during sleep, when the external anal sphincter relaxes involuntarily. This explains a phenomenon that has puzzled many sleeping partners.
Health Implications of Regular Suppression
Occasional gas suppression is harmless. However, chronically holding in gas is associated with several negative outcomes. Persistent pressure in the rectosigmoid region can contribute to diverticular disease progression in susceptible individuals. Prolonged distension may lead to rectal desensitization over time, potentially affecting the normal defecatory reflex. Bloating and abdominal discomfort are the most immediate consequences. There is no credible evidence that gas suppression causes intestinal rupture — the colon is remarkably compliant — but the discomfort alone provides good reason to find a private moment. Your colon will thank you.
Did You Know?
- The external anal sphincter can maintain voluntary contraction for several minutes before discomfort becomes acute.
- Retained hydrogen and methane can be detected on a breath test — used clinically to diagnose SIBO and lactose intolerance.
- The colon can accommodate up to 3 liters of gas without rupturing under pathological conditions.
- Rectal gas pressure is monitored in clinical manometry studies using balloon probes inserted rectally.
Fun Fact
A 2019 study at the Royal Victoria Hospital, Belfast, used MRI to track gas movement in real time during suppression events, confirming that retained gas migrates retrograde into the proximal colon within minutes of suppression (Marciani et al., 2019).
Sources
- Azpiroz, F. & Malagelada, J.R. (1987). Physiological variations in canine intestinal tone measured by an electronic barostat. American Journal of Physiology, 252(5), G601–G607.
- Serra, J. et al. (2001). Mechanisms of intestinal gas retention in humans: impaired propulsion versus obstructed evacuation. American Journal of Physiology, 281(1), G138–G143.
- Levitt, M.D. & Bond, J.H. (1970). Volume, composition, and source of intestinal gas. Gastroenterology, 59(6), 921–929.
- Suarez, F.L. & Levitt, M.D. (2000). An understanding of excessive intestinal gas. Current Gastroenterology Reports, 2(5), 413–419.