According to WebMD, mild or severe symptoms of lactose intolerance occur 30 minutes to 2 hours after ingesting milk or dairy products, and the most common side effects from a lactose intolerance are bloating, stomach cramps, gurgling sounds in the lower abdomen, gas, loose stools, diarrhea, foamy stools or vomiting. Lactose intolerance is recognized as a problem when these symptoms present every time dairy products are consumed.
WebMD explains that lactose intolerance can develop at any time. Adult lactose intolerance starts in the early teen and adult years. If the symptoms persist after ingesting dairy, then it may be safe to assume that a lactose intolerance has developed. Lactose intolerance is not the same condition as a dairy allergy, which presents as a much more violent reaction.
The American Academy of Pediatrics states that lactose intolerance can be recognized by conducting an elimination diet. Remove all dairy products from the diet for at least two weeks to see if the symptoms are relieved. After that, slowly reintroduce dairy products into the diet to see if the lactose intolerant symptoms return. If they do, then it is likely that a lactose intolerance is present. A doctor can run a battery of tests to confirm the lactose intolerance.