According to Dr. Arnold Levy, a gastroenterologist in Washington and vice president for education of the American Digestive Disease Society, "Precious little data are available anywhere in any language on the effects of hot, spicy foods on the digestive tract." Dr. Levy noted that some people experience gastrointestinal burning or intense stomach cramping when they eat spicy foods, but that different people are sensitive to different foods, a fact that they usually discover on their own and can then avoid the offending foods.
Too much spicy food/spices can give you indigestion, upset stomach, and/or heartburn. However, spicy food can also help your circulation, heart, lungs, and digestion in the right quantities (and if you can handle the spiciness). Things like Cayenne (one of the spiciest peppers) are used for a lot of different health benefits because of the naturally occurring Capsaicin (the part that makes the pepper hot)... the Capsaicin is actually what gives the health benefits.
Scientists have discovered the key to the ability of spicy foods to kill cancer cells.
They found capsaicin, an ingredient of jalapeno peppers, triggers cancer cell death by attacking mitochondria - the cells' energy-generating boiler rooms.
Source: http://news.bbc.co.uk/2/hi/health/6244715.stm
