Not everyone who has lactase malabsorption or lactose deficiency has lactose intolerance. Only those with digestive symptoms have lactose intolerance. Many people with lactase malabsorption and lactose deficiency can consume some milk products without issue. The amount of lactose people can tolerate varies. 

Is It a Milk Allergy? 

Often, people confuse lactose intolerance with an allergy to milk. Although lactase malabsorption and lactose deficiency are disorders, a milk allergy is more likely a reaction to milk proteins by the body's immune system. An allergy to milk may show itself with the consumption of a small amount of milk or milk products, and just this tiny amount may be life-threatening. Milk allergies generally appear in the first year of life. 

Four Types of Lactase Deficiency 

Primary lactase deficiency: This condition is also referred to as "lactase non-persistence." This is the most common type of lactase deficiency, showing in people whose lactase production has declined over time. Usually, this decline begins around age two but may show itself later in life. Children with lactase deficiency might not show symptoms until adulthood or adolescence.