How common is lactose intolerance in infants during the first year of life?

Lactose intolerance in infants during the first year of life is considered uncommon. Most infants are born with a natural ability to digest lactose, which is the sugar found in breast milk and formula. This ability is essential for their nutrition, as breast milk is the primary source of nourishment during the early months of life.

In fact, primary lactose intolerance, which is the inability to digest lactose due to decreased levels of lactase enzyme, typically does not manifest until later in childhood or adulthood. In infants, lactose intolerance is rare, as they generally possess high levels of lactase to effectively break down lactose for energy.

While some infants may experience temporary lactose malabsorption due to gastrointestinal infections or other health issues, these cases are not reflective of a true intolerance and often resolve quickly as the underlying condition is treated.

As a result, the notion that lactose intolerance is "common" or "very common" during infancy does not align with the typical developmental pattern of an infant's digestive system, reinforcing why it is classified as uncommon in this population.