The sugar contained in milk is called lactose, which is formed from two other organic substances known as glucose and gelatos. The enzyme responsible for the digestion of lactose is lactase and due to insufficient secretion of lactase, lactose present in the milk cannot be properly digested and the undigested lactose goes to the intestine and causes intestinal cramps and other symptoms of lactose intolerance.

Lactose intolerance in babies as well as in adults is common throughout the world and a most recent survey says that seventy five percent of the total population of the planet has all the symptoms of lactose intolerance due to the lower secretion of lactase and hence lactose intolerance in babies is a common and important issue.  

Symptoms of lactose intolerance in babies include acute pain in the lower backside of the abdomen, loose motion, excessive production of gas, vomiting and intestinal cramp. Babies will cry due to acute pain and cannot be consoled, sign of pain can be directly observed after the consumption of mother's milk or cow milk or any dairy products, and even if a baby is sleeping, the baby will wake up from the sleep due to intense pain. Severe pain in the stomach or lower back side of the abdomen will start within 30 to 180 minutes after the consumption of milk or any milk product. In some rare cases babies having lactose intolerance, can also develop eczema.

Lactose intolerance in babies is mainly caused due to the genetic factor i.e. babies inherit the gene responsible for Lactose intolerance in the baby from their parent. In other cases, babies develop it due to the intake of some medications. Some prematurely born babies also develop lactose intolerance for a short period.

There are some clinical tests for lactose intolerance in babies. Give your baby non lactose based food or food containing very little amount of lactose for a week and observe whether your baby develops the symptoms of Lactose intolerance in babies and if your baby develops the symptoms of lactose intolerance then your baby suffers from lactose intolerance. The hydrogen breath test is another alternative to know with certainty that one's baby suffers from lactose intolerance. In this test one is asked to give no food to one's baby at night and in the next morning one is asked to give one's baby a little amount of milk and breath samples of the baby are taken at a regular interval of time to find traces of hydrogen and if a baby suffers from lactose intolerance the baby will show an increased level of hydrogen in the breath. 

However, it can be said that lactose intolerance in babies is a common but not a serious issue. There is also no proper remedy for it. One can feed one's baby with milk, which has the lower content of lactose or can administer pills orally which increases the secretion of lactase.