Why do dogs get upset stomachs – common causes and treatments Normal functioning of the digestive system is one of the key signs of good health - in humans and animals. This topic is difficult to discuss without getting distasteful, but essentially, when there’s a digestive upset, the consequences are that food is rejected by the body. This can happen directly from the stomach (vomiting) or from the intestines (diarrheoa). These signs are common in dogs, and owners often wonder about the best way to deal with them. What causes an upset stomach in dogs There are many possible causes of vomiting and diarrhoea in dogs: entire textbooks have been written on the topic. The most common cause is simple: scavenging. Dogs have evolved to “eat first and ask questions later”. (Cats are far more finicky eaters, and as a result, they are less likely to suffer from this type of upset). When a dog eats something that really ought to have been left alone (the list of possibilities is too long to itemise), the consequence is commonly that their digestive tract becomes inflamed (red and irritated). Inflammation of the stomach causes muscle contractions which result in vomiting Inflammation of the intestines causes muscle contractions which cause increased speed of the intestinal contents through the digestive tract: there is not enough time for the fluid component to be absorbed back into the body, which explains why diarrhoea is the result. There are many other possible causes of an upset digestive system, including diet, viruses, bacteria, allergic reactions and parasites.