Those who were born prematurely are at an increased risk of the condition. This is because the enzyme lactase increases in production in the third trimester of pregnancy, so babies born early may have limited lactase production. 

Anyone who suffers from small intestine diseases may be more likely to develop lactose intolerance. Diseases such as celiac disease, Crohn's disease and bacterial overgrowth can affect a person's lactose tolerance. 

Finally, some treatments for cancer can cause lactose intolerance. Some develop intestinal troubles from chemotherapy, and radiation for abdominal cancers can increase risk of lactose intolerance.