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symptoms of lactose intolerance

Signs and symptoms of lactose intolerance

Lactose intolerance is a common digestive disorder that occurs when the body is unable to digest lactose, a type of sugar found in milk and dairy products. Symptoms of lactose intolerance usually develop within a few hours of consuming food or drinks that contain lactose.

The condition, which is also called lactose malabsorption, is usually harmless, but its symptoms can cause discomfort. Developed due to the lack of an enzyme called lactase, you might only experience the symptoms if your lactase levels are too low.

This may be the reason why most people with lactose intolerance can manage this condition without having to give up dairy products completely.

For breastfeeding infants, the lactase enzyme may be important to digest breast milk. As children grow older, however, the production of this enzyme may reduce. During adulthood, the production of this enzyme drastically reduces, resulting in symptoms of lactose intolerance.

Apart from these causes, there may be instances in which people develop lactose intolerance after surgery or due to gastrointestinal diseases such as viral or bacterial infections.


The signs and symptoms usually begin around 30 minutes to two hours after eating or drinking items that contain lactose. These may include:

  • Stomach pain and bloating

This might be the most common symptom of lactose intolerance in children and adults alike.

If your lactase enzyme levels are too low, your stomach may be unable to break down the lactose, which will then pass through your gut and into your colon. Bacteria in your colon may ferment lactose, releasing short-chain fatty acids and gas, causing bloating, stomach pain, and cramps around the navel and the lower part of the stomach. 

  • Diarrhoea

If you are lactose intolerant, you may experience an increase in water volume in your colon, which may increase the volume and liquid content of the stool. 

When the bacteria in your colon ferment the excess lactose, the fatty acids that are produced cause an increase in the amount of water the body releases into the colon. 

The acids that aren’t absorbed back into the colon and the increase in lactose can cause diarrhoea or an increase in the frequency, liquidity or volume of stool.

  • Increased gas

Gas is released during the fermentation process of excess lactose in your colon, increasing the levels of hydrogen, methane, and carbon dioxide.

The amount of gas produced may differ enormously from person to person due to differences in the efficiency of the bacteria responsible for fermenting lactose in the colon. 

Since the bacteria in the colon becomes efficient at fermenting lactose into acids and gases, people who have lactose intolerance may experience an increase in flatulence.

  • Constipation

Characterised by hard, infrequent stool, incomplete bowel movements, stomach discomfort, bloating, and excessive straining, this is one of the more unpleasant symptoms of lactose intolerance.

When bacteria in the colon ferment undigested lactose, they produce methane. Methane is thought to slow down the time it takes for food to move through the gut, leading to constipation. 

Due to the lack of research on the relationship between methane and constipation, this symptom may not be reported as a symptom of lactose intolerance.

  • Other symptoms

While most of the recognised symptoms of lactose intolerance are gastrointestinal, people with lactose intolerance may also experience other symptoms.

These symptoms may include: headaches, fatigue, loss of concentration, muscle and joint pain, mouth ulcers, urinating difficulties, and eczema. These symptoms, however, may not be directly connected to lactose intolerance and may have more to do with an allergy to milk (It’s important to note that lactose intolerance and milk allergy are two different conditions.).

Request more information on the symptoms of lactose intolerance

Lactose intolerance symptoms may be more common and be seen across several other gastrointestinal diseases. Because of this, it’s important to consult a team of expert gastroenterologists to get an accurate diagnosis before removing dairy from your diet.

Please note that due to COVID-19, our clinic has revised its safety protocols to protect the health and wellbeing of our patients and staff.