Lactose is the sugar found in milk products. Lactose intolerance is a condition where a person lacks the enzymes necessary to digest lactose. The enzyme is called lactase. Its action facilitates the hydrolysis of lactose into the simpler sugars glucose and galactose. When lactose cannot be digested properly symptoms including nausea, gas, diarrhea, and vomiting as well as stomach rumbling can occur. Irritable bowel syndrome is due in many cases to lactose intolerance. Since normally, mammals are weaned from mother's milk after a certain age, the enzyme lactase is no longer produced because the older organisms stop the consumption of milk. However, humans of all ages consume dairy products and lactase persists into adulthood. However, depending on the culture and diet practices followed there, decreased lactase varies worldwide depending on how much dairy is consumed.