Even if you can down curry vindaloo or burritos doused in hot sauce without flinching, your body might not be able to hold its poker face as well. Spicy foods can provoke indigestion, heartburn and loose stools in many people, though others can eat them with no problems. These issues stem from the chemical composition of spicy foods and how they interact with your body.
Spicy foods cause a burning sensation in your mouth because of the chemical compounds they contain, such as capsaicin in chili peppers and cayenne peppers. Your body does not break down these compounds during digestion, and they can cause irritation to the lining in your stomach and intestines. As a result, food sometimes moves more quickly through your digestive tract, resulting in loose stools. The compounds are in these stools and also can irritate the anus as they come out, which is why you'll sometimes feel a burning sensation during bowel movements after eating spicy foods.
If you experience diarrhea constantly after eating spicy foods, you might have a condition known as irritable bowel syndrome. This is a fairly common condition in which the nerves and muscles in your bowels are more sensitive than normal, meaning certain foods -- including spicy foods -- cause diarrhea, abdominal pain and a feeling of bloating. IBS is not life-threatening, and doctors can suggest ways to keep it under control. Caffeine, fatty foods and dairy products also can cause IBS flareups, so doctors recommend keeping a food journal to help you pinpoint exactly what foods cause adverse reactions.
Although diarrhea induced by spicy foods is unpleasant and uncomfortable, there's little evidence suggesting it causes long-term damage to your digestive system. A study published in the "Journal of the American Medical Association" in 1988 noted no damage to the stomach and small intestines after subjects ate spicy meals. The study went as far as to puree 30 g of jalapeno peppers and put them directly into the stomach, which caused no damage. Furthermore, spicy foods do not cause ulcers, although the irritation they cause can make the pain from ulcers worse.
If you are susceptible to diarrhea after spicy foods, the easiest prevention is to avoid them altogether, but taking steps to improve your overall digestive health can help if you still want the occasional indulgence. Increasing your fiber intake by eating more fruits and vegetables or drinking more water improves digestion, as does eating regular meals. Over time, your body might even become more accustomed to spicy foods, and they might have certain health benefits, such as lowering blood pressure. If your diarrhea persists for several days, spicy food likely is not the cause, so you should consult a doctor to make sure it's not something more serious.