A twenty-something gentleman presented to the walk-in clinic a few years ago with severe diarrhea. He was working at a feedlot where he was exposed to cattle and all their byproducts, and he admitted that his hand-washing skills were not ideal. He had been ill for a few days, was getting dehydrated, and now there was blood in the stool, more than you would expect from just hemorrhoids. An estimated two to five billion episodes of diarrheal illness occur every year worldwide, mostly from infection in infants. In 2013 more than one and a quarter million people, mostly babies, died from dehydration due to diarrhea, mostly the consequence of contaminated water. It is in the amazing small intestine and colon where roughly two gallons of fluid flow-through daily only to be reduced to about a half-a-cup of fluid that exits in the stool, that is unless something goes wrong. The word diarrhea literally means through-flow. The electrolyte explanation for what causes diarrhea runs-on like a chemistry teacher on too much caffeine. But suffice it to say that we are still learning the complexities of such a system that, when working correctly, turns the stuff we shove into our mouths into micronutrients and water and then carries the necessary parts of this slurry into the blood stream in order to keep us alive and working. Non-infectious causes of diarrhea include problems like shortened bowel, partial blockages, immune problems like Crohn’s disease and Ulcerative Colitis, and intolerance to certain foods like milk products and the gluten in grain. The diagnosis for infectious diarrhea is made primarily from the patient’s history or story. Clues for the cause can include previously attending a day care or anywhere diarrhea illness is present; working where there is exposure to animals; eating undercooked or spoiled food; and traveling to another country south of the border. Antibiotics are rarely needed to treat infectious diarrhea, and in contrast, life-threatening diarrhea can result from an exposure to antibiotics. The most challenging cause for diarrhea comes when a person is burdened with a very nervous and sensitive bowel, called Irritable Bowel Syndrome or IBS. This diagnosis is made when everything else is ruled out. A professional should evaluate any diarrhea lasting longer than a week and produces internal bleeding. I admitted my patient to the hospital for IV fluid hydration, the diarrhea resolved spontaneously without antibiotics, and he vowed to do better with washing his hands.