Milk is an incredibly nutritious food source that has sustained humans for over 10,000 years, dating back to the domestication of ruminants. It serves as a rich source of calcium, protein, and essential vitamins. However, not everyone can partake in the wide array of dairy products available in the market, particularly those who suffer from lactose intolerance or a dairy allergy. While both conditions are distinct, they are often mistakenly conflated, leading to unnecessary dietary limitations for many individuals. This article delves into the key differences between lactose intolerance and dairy allergy, aiming to clarify these common misconceptions.

Understanding Lactose Intolerance

Lactose intolerance is a condition characterized by the body's inability to effectively digest lactose, a sugar found in dairy products. This syndrome often arises when individuals consume lactose-rich foods, leading to discomfort or digestive issues.

Lactose serves as the main carbohydrate in cow’s milk and is a crucial component of an infant's diet. However, as children mature and their intake of milk and dairy products decreases, the body's production of the enzyme necessary to digest lactose also declines.

The enzyme lactase is essential for breaking down lactose into glucose and galactose, which can then be absorbed in the small intestine. When there is a reduced activity of lactase in the brush border of the small intestine, a condition known as lactase deficiency emerges, contributing to lactose intolerance, which ranks among the most prevalent food intolerances worldwide.

Categories of Lactase Deficiency

There are four recognized categories of lactase deficiency that result in lactose intolerance:

• Primary Lactase Deficiency: This is the most prevalent form, affecting 70–75% of adults globally. Genetically determined, it is also referred to as lactase non-persistence. In this case, lactase production declines significantly around the age of two, leading to symptoms that may persist into late adolescence or adulthood.
• Secondary Lactase Deficiency: This temporary condition arises from damage to the small intestine caused by infections, food allergies, or conditions such as Crohn's disease or celiac disease. Typically, addressing the underlying cause can enhance lactose tolerance.
• Developmental Lactase Deficiency: Frequently observed in premature infants, this type occurs because the cells that produce lactase in the small intestine develop later in the third trimester. It usually resolves shortly after birth.
• Congenital Lactase Deficiency: This exceedingly rare genetic disorder results in the small intestine producing little to no lactase enzyme from birth.

As illustrated, a significant portion of the adult population worldwide experiences lactose intolerance after the infant stage, with only a minority exhibiting lactase persistence, where lactase production continues throughout adulthood.

Research indicates that many individuals with lactose intolerance can tolerate some amount of lactose without experiencing significant symptoms. Evidence suggests that they may be able to consume up to 12 grams of lactose in one sitting — equivalent to the quantity found in approximately 1 cup (240 mL) of milk. However, tolerance levels can vary widely among individuals.

Consequently, the management of lactose intolerance primarily emphasizes reducing lactose intake rather than complete elimination from the diet.

Lactose intolerance arises from the body's inability to digest and absorb lactose due to a decrease in lactase enzyme production — a key carbohydrate found in dairy.

Understanding Dairy Allergy

Dairy allergy, often referred to as cow's milk allergy, ranks among the most prevalent food allergies globally. Similar to peanut and tree nut allergies, it is also a significant contributor to cases of allergy-induced anaphylaxis.

This condition arises when the immune system mistakenly identifies certain proteins in cow's milk as harmful, prompting a defensive response. In essence, the body perceives these proteins as threats, triggering an immune reaction aimed at neutralizing them.

Upon subsequent exposure to the same protein, the immune system recognizes it and responds by releasing various chemicals known as immune mediators. This reaction can lead to the onset of symptoms associated with cow's milk allergy.

Typically, this allergy manifests during early childhood, particularly within the infant's first year, and many children tend to outgrow it by the age of six. Most children who are allergic to cow's milk tend to react to both casein and whey, the two primary proteins found in milk.

Management of this allergy involves adhering to a strict diet that excludes cow's milk. For nursing mothers, it is essential to avoid dairy products, as cow's milk protein can be transmitted through breastmilk.

Symptoms

Lactose intolerance and cow’s milk allergy can manifest through a variety of symptoms, encompassing both digestive and non-digestive issues. While they exhibit some overlapping symptoms, each condition also presents unique characteristics that distinguish them from one another.

The symptoms of lactose intolerance arise from the bacterial fermentation of undigested lactose within the colon, leading predominantly to digestive issues that typically occur between 30 minutes to 2 hours after dairy consumption.

Conversely, the symptoms related to cow’s milk allergy can differ based on whether they are IgE-mediated or non-IgE-mediated:

• IgE-mediated symptoms: Often referred to as rapid-onset reactions, these symptoms can present within minutes of ingestion and are frequently associated with skin and respiratory issues, and in severe instances, may lead to anaphylaxis.
• Non-IgE-mediated symptoms: These slow-onset symptoms usually manifest as delayed reactions, primarily affecting the skin and digestive system.

1. Shared Symptoms

Both lactose intolerance and cow’s milk allergy exhibit a range of digestive symptoms, which often leads to confusion between the two conditions. Common symptoms include:

• Nausea
• Abdominal pain
• Diarrhea

2. Lactose Intolerance Symptoms

In addition to the aforementioned symptoms, lactose intolerance can trigger other digestive issues such as flatulence, constipation, borborygmus (stomach rumbling), and bloating.

Interestingly, up to 20% of individuals with lactose intolerance may also experience non-digestive symptoms, which may include headaches, dizziness or vertigo, memory lapses, difficulty concentrating, muscle and joint discomfort, mouth ulcers, fatigue, and overall sluggishness.

3. Cow’s Milk Allergy Symptoms

Symptoms that are unique to cow’s milk allergy predominantly impact the respiratory system and skin. Common manifestations include hives, wheezing, oral itchiness, swelling of the lips, tongue, or throat, shortness of breath, and vomiting.

In severe cases, anaphylaxis may occur, representing a critical medical emergency that can be life-threatening if not addressed promptly, as it may lead to airway constriction or a drastic drop in blood pressure.

While lactose intolerance and cow’s milk allergy share certain digestive symptoms such as nausea, abdominal pain, and diarrhea, each condition is accompanied by its own unique set of symptoms that can impact various bodily systems.

Risk Factors

Several risk factors can elevate the likelihood of developing either lactose intolerance or a cow’s milk allergy.

Risk Factors for Lactose Intolerance

As individuals age, most humans tend to reduce the production of lactase, the enzyme responsible for digesting lactose, with only a small percentage maintaining their ability to digest it into adulthood.

The onset and prevalence of lactase decline can significantly differ across various ethnic groups worldwide.

Global data regarding the prevalence and timing of lactose intolerance indicates that its occurrence may be found in:

• over half of the population in regions such as South America, Africa, and Asia
• nearly all individuals in several Asian nations
• children of African, Asian, or Hispanic descent, typically showing symptoms between the ages of 2 to 3 years
• children of European and American descent, where symptoms usually emerge between 5 to 6 years of age or during their teenage years

Conversely, the trait of lactase persistence is notably more common among northern European populations.

Risk Factors for Cow’s Milk Allergy

In contrast to lactose intolerance, cow’s milk allergy frequently resolves by the age of 6, largely affecting children and impacting approximately 1 to 2% of infants.

Research indicates that male children who suffer from additional allergies—such as multiple food allergies, asthma, atopic dermatitis, and allergic rhinitis—are at a twofold increased risk for developing cow’s milk allergies.

Ethnic background may also influence susceptibility, with findings suggesting that non-Hispanic Black and non-Hispanic white children exhibit a higher likelihood of developing cow’s milk allergy.

Thus, while the main risk factor for lactose intolerance appears to be linked to ethnicity, the risk factors for cow’s milk allergy are primarily associated with male children who have multiple allergies.

Diagnosis

Lactose intolerance and cow’s milk allergy are distinct conditions, each requiring different diagnostic approaches.

To identify lactose intolerance, several common tests are utilized:

• Lactose breath test (LBT): This popular diagnostic method is a quick, non-invasive procedure that assesses hydrogen levels in the breath after administering a lactose dose of 20–50 grams, following an overnight fast of 8–12 hours. A hydrogen concentration exceeding 20 parts per million (ppm) indicates a positive result.
• Lactose tolerance test: This blood test ranks as the second most prevalent method. It evaluates the rise in blood sugar levels after lactose consumption. If blood sugar levels fail to exceed 1.1–1.4 mmol/L, it suggests that lactose digestion and absorption are inadequate.
• Genetic test: This test explores genetic variations linked to lactase persistence and non-persistence. However, it is less frequently conducted due to its expense.
• Intestinal biopsy: An intestinal biopsy examines lactase enzyme activity in the intestine. Similar to the genetic test, it is not commonly performed due to its invasive nature and associated costs.

Conversely, cow’s milk allergy is diagnosed through various primary tests, including:

• Double-blind, placebo-controlled oral food challenge: This is regarded as the gold standard for diagnosing food allergies. A healthcare professional administers small amounts of the suspected allergen, progressively increasing the dose until a reaction occurs.
• Skin prick test: In this test, the skin is pricked with a lancet that contains a drop of the allergen. A wheal measuring at least 3 mm larger than the negative control is deemed positive, although false positives can happen and are best interpreted by an allergist or immunologist.
• Specific serum IgE: This test quantifies the IgE levels in the blood that may trigger a reaction when exposed to milk proteins. While it predicts the likelihood of an allergic response, it alone cannot confirm a diagnosis since it often results in false positives.

In summary, lactose intolerance and cow’s milk allergy can be assessed through a variety of diagnostic methods, ranging from minimally invasive to more invasive techniques.

The Bottom Line

Both lactose intolerance and cow’s milk allergy represent distinct conditions triggered by dairy consumption. Lactose intolerance stems from the body's inability to effectively digest lactose, a type of carbohydrate, while cow’s milk allergy is an immune response to the proteins in milk.

Although they can manifest similar symptoms such as nausea, diarrhea, and abdominal discomfort, lactose intolerance and cow’s milk allergy impact the body in different ways and therefore require separate treatment strategies.