Fact Checked

5 Signs & Symptoms of Lactose Intolerance

Dr. Bhavani A

Do you feel gassy or bloated after having a milkshake or ice cream?

More often than not, milk and dairy products are believed to be healthy food items and are a necessary part of a healthy diet. However, there are instances when the body isn’t able to digest dairy items leading to several health complications. Such a condition is better known as lactose intolerance or milk protein intolerance.

Lactose is a sugar found in milk. Most mammals’ milk contains lactose. When humans consume milk, an enzyme called lactase helps break down the lactose and aids digestion. Infants, in particular, need lactase to help digest breast milk. The body produces lesser lactase with age and by the time most people become adults, it cannot produce enough lactase to digest milk sugar. This is when the body becomes lactose intolerant and shows several signs to suggest so.

Here’s a quick look at five such symptoms that hint at lactose intolerance among humans:

Bloating and stomach cramps

These are very common symptoms that suggest lactose intolerance.  When the lactose cannot be broken down, it reaches the colon through the gut. Fermentation of the lactose in the colon releases acids and gases that cause cramps and pain in the stomach. The increase of gases and water in the colon stretches the gut wall that can lead to a bloating sensation in the stomach. This is also called distention.

Nausea and vomiting

With the bloating and stomach pains, a feeling of nausea and the urge to vomit can be noticed, too. While not very common, it has been observed.


The increase in water in the colon caused by the acids and undigested lactose leads to diarrhoea. This is characterized by the increase in liquid content in stools. This symptom is largely seen in children than in adults. However, do note that diarrhoea might not always be caused by lactose intolerance. Indigestion, overeating, etc. can also be possible causes.


An even rarer symptom of lactose intolerance than diarrhoea is constipation. This is usually characterized by an uncomfortable sensation of incomplete bowel movements, bloating and discomfort in the stomach, infrequent passing of stools among others. Constipation because of lactose intolerance happens because the lactose ferments in the colon leading to the formation of methane. This is believed to slow the food moving through the gut.


Lactose fermentation in the colon leads to increased production of gases like methane, hydrogen and carbon dioxide. This leads to increased flatulence. Although it must be noted that caused by lactose fermentation, the resultant flatulence is odourless. The extent of gas formation differs with every individual suffering from lactose intolerance; it depends on how efficient the colon microflora is at the lactose fermentation stage.


Lactose intolerance can be of three types–primary, secondary lactose, and congenital lactose intolerance. The most commonly observed type is primary lactose intolerance. This happens when the body, with age, begins to produce lesser amounts of lactase. Secondary lactose intolerance is when the lactase production by the small intestine is affected after an injury, surgery or illness. While congenital lactose intolerance is rare, it has been noticed that some babies are born with the condition wherein the body shows no lactase production at all.

The symptoms suggested may not always indicate lactose intolerance. Hence, it would be a good idea to consult a doctor if these symptoms occur frequently and especially after consuming dairy items.

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