Secondary lactase deficiency: In most cases, secondary lactase deficiency is caused by injury, infection, disease or other issues that affect small intestine. Sometimes, treating the cause of the problem helps the symptoms of lactose intolerance due to secondary lactase deficiency. 

Developmental lactase deficiency: This condition may occur in premature babies. Usually, developmental lactase deficiency only lasts a short while after babies are born. 

Congenital lactase deficiency: This disorder is an extremely rare case in which the small intestine produces very little lactase from the time of birth. This disorder is hereditary and present at birth. 

Who Has Lactose Intolerance? 

Generally, in the United States, a few racial and ethnic populations are more likely to exhibit lactose intolerance than others. The groups more likely to be affected are African Americans, Hispanic/Latinos, American Indians and Asian Americans. Lactose intolerance is less likely to occur in people of American or European descent.