What causes lactose intolerance?

Lactose intolerance is primarily caused by the body's reduced ability to produce lactase, the enzyme responsible for digesting lactose, which is the sugar found in milk and dairy products. When an individual has lactose intolerance, it means that their small intestine does not produce enough lactase to effectively break down lactose, leading to gastrointestinal symptoms such as bloating, gas, diarrhea, and stomach cramps after consuming lactose-containing foods.

This condition is largely genetic and often develops with age, as the production of lactase typically decreases after weaning in many individuals. As a result, even normal consumption of lactose may lead to discomfort for those with lactose intolerance, not because they are consuming excessive amounts, but rather because their bodies are unable to properly digest the lactose present.

Other choices present alternative misconceptions: excessive lactose consumption could be a contributing factor to symptoms in those with lactose intolerance, but it is not the underlying cause; an allergic reaction to milk proteins characterizes a different condition (milk allergy) that involves the immune system, rather than an enzymatic deficiency; and stating intolerance to all dairy products is incorrect as some individuals with lactose intolerance can tolerate certain dairy products, especially those lower in lactose, like hard cheeses or yogurt.