Lactose Intolerance 

If you had received a radiation therapy of cancer in your abdomen or have intestinal complications from chemotherapy, you may have increased a risk of lactose intolerance. 

.Small intestine problems can cause lactose intolerance including bacterial overgrowth, celiac disease and Chron's disease. 

Lactose Intolerance usually appears in adulthood becuase it is caused by a  decreasing activity of the LCT genes after infancy. Some individuals have inherited changes in this element that leads a sustainded lactase production in the small intestine and the ability to digest lactose. People that don't inherit these changes have a reduced activity to digest lactose as they get older resulting in the symptoms of lactose intolerance.   

Lactose intolerance is most common in African, Assian, American indian descent and Hispanican people. 

Kids born prematurely may have reduced levels of lactase because their small intestine dosen't develops lactase-producing cells until the end of the third trimester.