Why Am I Suddenly Lactose Intolerant? Here’s Your Answer: HealthifyMe

Why Am I Suddenly Lactose Intolerant? Here’s Your Answer: HealthifyMe

Lactose intolerance arises when your body struggles to break down lactose, the natural sugar present in dairy products. It occurs primarily when your small intestine lacks sufficient lactase, an enzyme vital for lactose digestion. 

The onset of lactose intolerance can happen at any point in life, irrespective of prior experiences with milk and its products. While some people deal with lifelong lactose intolerance from childhood, others may develop intolerance as they age. Additionally, the production of lactase can either diminish significantly or cease altogether during the transition to adulthood and beyond. Medical conditions disrupting the gut’s health and functionality are the common triggers for the sudden onset of lactose intolerance.

Lactose Intolerance: An Overview

Lactose intolerance is when the body struggles to digest lactose, a natural sugar in milk and most dairy products. Breast milk and standard infant formulas also contain lactose as the primary dietary sugar. When undigested lactose passes through the large intestine, it can lead to discomfort, including symptoms like gas, abdominal pain, and bloating. 

The extent and severity of lactose intolerance vary from person to person. While some may experience difficulty digesting any amount of milk products, others can tolerate modest amounts or specific types without issues.

There is a broad spectrum of lactose intolerance, ranging from individuals with no tolerance for dairy to those who can digest certain dairy products like milk chocolate, hard cheeses or yoghurt. The four main types of lactose intolerance include:

Primary Intolerance

People who experience primary lactose intolerance initially produce sufficient lactase in the infant stage and childhood. As children transition to a more varied diet, the natural decline in lactase production occurs. However, it typically remains at a level sufficient to digest the amount of dairy in a standard adult diet. In cases of primary lactose intolerance, lactase production experiences a significant decline by adulthood, making the digestion of milk products challenging. It is the most common type of lactose intolerance. 

Secondary Intolerance

Damage to the gut lining, where lactase is produced, leads to secondary lactose intolerance. The common triggers are gut infections, illnesses, or intestinal surgery. It is also known as acquired lactase deficiency.

Developmental Intolerance

Developmental intolerance occurs in prematurely born babies due to underdeveloped small intestines, leading to temporary lactose intolerance.

Congenital Lactose Intolerance

Congenital lactose intolerance is a condition affecting infants. It is a rare condition that arises when infants are born with a deficiency or absence of the enzyme lactase. This condition occurs when babies receive one gene responsible for this deficiency from each parent despite both parents being lactose tolerant. 

Signs and Symptoms of Lactose Intolerance

While less common, some lactose intolerant people have reported experiencing symptoms such as headaches, difficulty concentrating, muscle and joint pain, fatigue, mouth ulcers, problems with urination, and eczema. The following are the five most commonly observed signs and symptoms of lactose intolerance.

Stomach Pain

The cells lining the colon cannot absorb carbohydrates like lactose. However, naturally occurring bacteria, known as microflora, ferment and break down these carbohydrates. This fermentation process releases short-chain fatty acids, along with gases like hydrogen, carbon dioxide, and methane. This accumulation of acids and gases causes stomach pain and cramps. The pain is typically concentrated around the navel and the lower abdominal region.


Lactose intolerance can lead to nausea and, in some cases, vomiting, particularly in children. In fact, nausea is the second most common symptom associated with lactose intolerance, following abdominal pain. The resulting gases and volatile fatty acids when lactose ferments in the gut are the main causative factors for inducing feelings of sickness. 


Lactose intolerance causes diarrhoea by increasing the water volume in the colon, consequently increasing the liquid content and overall volume of the stool. However, experiencing diarrhoea does not necessarily indicate lactose intolerance. Various factors such as diet, other types of malabsorption, medications, infections, and inflammatory bowel diseases can also contribute to this symptom.

Within the colon, the fermentation of lactose causes the production of short-chain fatty acids and gases. While the majority of these acids are reabsorbed into the colon, not all are. The remaining acids, along with unprocessed lactose, contribute to an increased release of water into the colon. It can cause diarrhoea or frequent, watery stools.

Gassy Feeling

The lactose fermentation in the colon increases the production of methane, hydrogen, and carbon dioxide gases, which further increases flatulence. Unlike when proteins break down in the gut, which can release smelly sulphur compounds causing the odour in flatulence, lactose fermentation mainly produces gases without a noticeable smell.


While diarrhoea is a more common lactose intolerance symptom, some may experience constipation instead. It occurs because the small intestine does not properly digest lactose, allowing it to move into the colon, where it may affect water absorption and reduce bowel movements.

While lactose intolerance and dairy allergy may share some symptoms and require the removal of dairy from one’s diet, they are different conditions. Lactose intolerance pertains to the digestive system, whereas dairy allergy involves the immune system. Although dairy allergy may manifest some similar symptoms as lactose intolerance, it is an immune system issue and can be more severe, potentially even life-threatening.

In addition to common symptoms such as bloating, gas, cramps, diarrhoea, and nausea, people with dairy allergy also experience respiratory problems, hives, and swelling of the throat and lips. It is crucial to recognise the difference between these conditions, as dairy allergy poses a heightened risk and requires careful management.

Causes of Sudden Lactose Intolerance

Lactose intolerance can develop at any age, including well into adulthood. It is because lactose intolerance is influenced not only by the expression of lactase but also by factors such as the cumulative intake of lactose over time, the composition of intestinal flora, and the sensitivity of the gastrointestinal tract. All these factors can change as you age. 

Sudden-onset lactose intolerance is typically categorised as secondary lactose intolerance, and the leading causes of this condition are below:

Illness or Injury

Intestinal diseases like celiac disease, Crohn’s disease, ulcerative colitis, inflammatory bowel disease (IBD), surgeries, or injuries to the small intestine cause sudden lactose intolerance. Drinking inadequately treated or untreated water can also cause damage to your bowel, potentially leading to lactose intolerance. Treating the underlying disorder may restore lactase levels.


A medication you are taking may increase your sensitivity to dairy. Common triggers include antibiotics. Ropinirole, Colchicine, Entecavir, and Zaleplon are some common drugs known to have lactose intolerance as a side effect. Additionally, there have been occasional cases where patients undergoing thionamide therapy and chemotherapy treatments experienced symptoms of lactose intolerance, including severe diarrhoea.


Typically, ageing increases sensitivity to digestive issues, such as feeling bloated after meals. Additionally, consuming caffeine or spicy foods that irritate the intestinal lining or stimulate the gut to contract more quickly can mimic symptoms of lactose intolerance.

Going Dairy-Free

People accustomed to including lactose in their diet possess significantly higher levels of the lactase enzyme, six to eight times more, compared to those who do not consume lactose. They are more efficient at digesting lactose, which helps prevent symptoms. However, abruptly eliminating high-lactose foods from your diet can lead to lactose intolerance symptoms upon reintroduction, at least temporarily. 

Refraining from consuming high-lactose foods can alter your colon bacteria, reducing the number of lactose-digesting bacteria. Consequently, reintroducing lactose in a substantial amount may lead to symptoms. Therefore, it’s advised not to adopt a dairy-free diet unless necessary. If you have already done so and wish to reintroduce dairy products, it is recommended that you do it gradually.

How to Manage Lactose Intolerance

If you suspect that you may be experiencing the symptoms of lactose intolerance, it is advisable to consult with a doctor. If you naturally avoid milk-based products, there is a risk of becoming deficient in essential nutrients such as calcium, vitamin D, riboflavin, and protein. Therefore, it is always recommended to seek guidance from a reputable platform like HealthifyMe and consult with a nutritionist. It will help you understand and create a diet plan that aligns with your body and lifestyle, ensuring you do not encounter any unwanted deficiencies or discomfort.

When adjusting to a lactose-free diet and lifestyle, carefully read food labels to identify ingredients containing lactose. Removing milk and its products from the diet can help manage symptoms. However, apart from milk, pay attention to ingredients derived from milk, including:

  • Cheese
  • Butter
  • Yoghurt
  • Margarine
  • Dry milk solids or powder
  • Whey or whey protein concentrate
  • Casein or caseinates
  • Curds

Note: Hard cheeses like cheddar and Swiss generally contain less lactose than soft cheeses. Yoghurt is also considered easier to digest than other dairy forms. 

You cannot prevent lactose intolerance, but you can minimise symptoms by consuming less dairy. Choosing low-fat or fat-free milk may also reduce symptoms. Consider trying dairy milk alternatives such as almond, flax, soy, or rice milk. Taking lactase pills or drops, such as Lactaid or Dairy Ease, before eating can also help manage symptoms.

You can still obtain sufficient calcium without consuming dairy through various sources. Some good non-dairy options for calcium include:

  • Calcium-fortified foods: These include juices, breads, and non-dairy milks like almond, soy, and oat milk. Soy-based products like tofu and tempeh can be excellent sources of calcium, especially if they are processed with calcium sulphate.
  • Boned fish: Fish with bones, such as sardines or salmon, are rich in calcium. It’s important to note that not all fish are high in calcium, and the calcium content can vary.
  • High calcium plant foods: Plant-based foods like kale, collard greens, bok choy, and broccoli contain reasonable amounts of calcium. 

HealthifyMe Suggestion

When you are lactose intolerant, it’s important to avoid dairy products and ingredients that contain lactose. Some common foods to watch out for include milk, cheese, yoghurt, butter, cream, ice cream, sour cream and certain processed foods that may contain lactose as an ingredient. Always check labels for terms like lactose, milk solids, whey, casein, buttermilk, and dry milk powder as these indicate the presence of dairy. Baked goods (cakes, cookies, pastries) may contain milk or butter, processed meats (like sausages and deli meats) may contain milk solids or whey, and salad dressings and sauces may use milk or cream as a base. When shopping, always carefully read labels and if you’re unsure about a product, it’s best to choose alternatives labelled as lactose-free or dairy-free. 

The Final Word

Secondary lactose intolerance, often sudden in onset, results from various causes such as illness, medication, ageing, and dietary changes. Addressing secondary lactose intolerance involves treating the root causes, such as illnesses or injuries to the intestines, medication-related sensitivities, and age-related changes. 

While minimising dairy consumption can alleviate symptoms, it’s essential to maintain adequate intake of essential nutrients like calcium, vitamin D, riboflavin, and protein. For effective management, seeking professional guidance, consulting with a doctor, and working with a nutritionist can help create a well-balanced diet that meets nutritional needs without causing discomfort. 

Disclaimer: The purpose of this article is just to disperse knowledge and raise awareness. It does not intend to replace medical advice from professionals. For further information, please contact our certified nutritionists Here.

Research Sources

Lactose Intolerance

Diarrhoea caused by carbohydrate malabsorption

Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

Lactose intolerance following antithyroid drug medications

Frequently Asked Questions (FAQs)

Q: Why am I suddenly experiencing symptoms of lactose intolerance when I never did before?

A: The sudden onset of lactose intolerance symptoms can be due to a reduction in lactase enzyme activity. Other factors are ageing, certain medications, medical conditions, or treatments such as chemotherapy, which can also trigger lactose intolerance.

Q: Can lactose intolerance develop later in life, and what are the factors that contribute to it?

A: Yes, a gradual onset of lactose intolerance often occurs due to genetic predisposition. In some cases, an injury or illness affecting the digestive system causes secondary lactose intolerance, even when lactase production was initially normal. Certain medications and chemotherapy can impact the digestive system and result in temporary lactose intolerance.

Q: Is it possible for a temporary condition to cause sudden lactose intolerance?

A: Yes, a temporary condition can cause sudden lactose intolerance. Infections or medical treatments affecting the digestive system might disrupt lactase production temporarily, causing lactose intolerance symptoms. Once the temporary issue is resolved, lactose tolerance may get better.

Q: How does stress or changes in lifestyle impact the onset of lactose intolerance symptoms?

A: High-stress levels for prolonged periods could flare up the symptoms of a pre-existing intolerance rather than directly causing them. Chronic stress makes the immune system more exposed, vulnerable, and sensitive to ”foreign” bodies. As a side effect, the body interprets lactose as an aggressive trigger.

Q: Are there specific medical conditions or infections that can trigger lactose intolerance?

A: Lactose intolerance occurs when the lactase production in your small intestine decreases following an injury, infection, or surgery involving the small intestine. Celiac disease, viral infection, bacterial overgrowth, and Crohn’s disease are some common triggers of secondary lactose intolerance.

Q: Can pregnancy be a factor in developing temporary or sudden lactose intolerance?

A: Yes, pregnancy can contribute to this because hormonal changes may impact the digestive system, potentially leading to symptoms resembling lactose intolerance, such as bloating, gas, and diarrhoea. However, in many instances, this is due to a temporary reduction in lactase enzyme activity.

Q: What role do genetics play in the sudden onset of lactose intolerance?

A: Lactose intolerance may result from a genetic predisposition causing a reduction in lactase production, the enzyme responsible for lactose breakdown in the digestive system. In instances where genetics play a role, the onset of lactose intolerance might be more gradual, yet it can still manifest unexpectedly.

Q: Is it common for individuals to mistake lactose intolerance for other digestive issues?

A: Common symptoms of lactose intolerance include bloating, gas, diarrhoea, and abdominal discomfort. These signs are nonspecific and are also observed in other digestive issues such as irritable bowel syndrome (IBS) or inflammatory bowel diseases. While lactose intolerance and dairy allergy may share some symptoms and require the removal of dairy from one’s diet, they are different conditions.

Q: Can certain medications or treatments lead to temporary lactose intolerance?

A: Cancer treatments, particularly those involving chemotherapy, may impact the digestive system and give rise to symptoms of lactose intolerance. Gastrointestinal infections or illnesses have the potential to harm the intestinal lining, influencing lactase production and resulting in temporary lactose intolerance. Additionally, certain antibiotics can disturb the gut’s bacterial balance, potentially leading to temporary lactose intolerance.

Q: How can one manage or cope with sudden lactose intolerance symptoms, and is it reversible?

A: Some people may find that they tolerate specific dairy products better than others. Experimenting with different types of dairy can help identify those causing fewer symptoms. Additionally, taking lactase supplements before consuming dairy may assist in preventing symptoms. It is crucial to recognise that while symptom management is feasible, lactose intolerance is typically considered irreversible.

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