Tummy upsetters are substances that can cause an upset stomach, such as ACIDS. ACIDS are a type of chemical compound that can be found in many foods and drinks, and they can cause irritation to the lining of the stomach. ACIDS can also be produced naturally by the body, and when too much is produced it can lead to an upset stomach. In this crossword, the solution for the term 'Tummy Upsetters' is 'ACIDS', which is a five letter word.