Dairy allergy vs. lactose intolerance: what’s the difference?

A dairy allergy, or a milk allergy, is an immune disorder triggered when an individual ingests milk products. It’s commonly triggered by cow’s milk, but sheep’s milk, goat’s milk, and other animal-derived milk can also lead to symptoms [1].

Dairy allergies primarily appear within the first 6 months of life [2]. When a dairy allergy is not mediated by immunoglobulin (IgE), one of the immune system’s primary antibodies, symptoms may take days or weeks to manifest. Gradual onset symptoms could include:

• Stomach cramps
• Diarrhea
• Bloody stool
• Colic (constant crying in infants)

In more severe cases, specifically when IgE is involved in the immune response triggered by dairy, symptoms may set in within minutes [3]. Rapid-onset symptoms may include [4]:

• Hives, swelling, or itching
• Wheezing or coughing
• Shortness of breath
• Vomiting
• Anaphylaxis

Rapid-onset dairy allergies are considered serious due to their potential to trigger anaphylactic shock [1].

During anaphylaxis, breathing passages constrict, making respiration extremely difficult, which triggers a significant lowering of blood pressure [5]. Because anaphylaxis requires immediate emergency treatment to avoid potentially fatal outcomes, identifying a dairy allergy early is critical for avoiding trigger ingredients and supporting young children’s well-being.

What causes a dairy allergy?

Like all food allergies, dairy allergies primarily pertain to the immune system. Lactose intolerance, in contrast, chiefly involves the digestive system.

When people with a dairy allergy ingest milk or milk products, their immune system reacts to two key proteins found in milk [4]:

• Caseins, a substance found in milk curds, the solid constituent in milk
• Whey, a substance found in the liquid part of milk [1]

This causes the immune system to release histamines, chemicals responsible for the inflammatory reactions underlying allergic symptoms [6].

While the mechanisms behind dairy allergies are well understood, the root cause of their occurrence is not fully known. Researchers estimate that approximately 4.9% of children younger than 3 years old present with a cow’s milk allergy, though there appears to be a lower incidence among infants who are breastfed [2,3].

Fortunately, many babies and young children with dairy allergies outgrow their condition by adolescence [2]. If you suspect a dairy allergy in yourself or your child, consider speaking with a healthcare professional. They can help evaluate symptoms, recommend appropriate testing, and provide guidance on dietary changes or allergy management strategies to help reduce the risk of severe reactions.

Lactose intolerance, or lactose malabsorption, refers to a condition in which an individual cannot digest lactose, a type of sugar constituent in dairy products, without experiencing digestive distress [7].

Lactose intolerance symptoms typically set in between 30 minutes and 2 hours after an individual has ingested foods containing milk [8]. Consuming milk or milk-based products can cause [8]:

• Gas and bloating
• Abdominal pain and cramps
• Nausea
• Vomiting
• Diarrhea

While uncomfortable, lactose intolerance is not considered a serious medical condition and can usually be managed with dietary and lifestyle adjustments [7].

Even so, living with lactose intolerance can interfere with an individual’s ability to meet their daily vitamin D and calcium quotas. For this reason, it’s critical to identify whether you have the condition to help ensure you meet your nutritional needs.

What causes lactose intolerance?

Lactose intolerance occurs when an individual lacks sufficient reserves of lactase, an enzyme responsible for processing lactose that is produced by the small intestine [9].

When lactase enzyme production falls short, lactose advances to the colon without being broken down into the simple sugars known as glucose and galactose. This causes bacteria to feed on unprocessed lactose, resulting in a string of uncomfortable digestive symptoms [8].

Not all forms of lactose intolerance occur in the same circumstances. Healthcare providers recognize three main types of lactose intolerance:

• Primary lactose intolerance - Of all the types of lactose intolerance, primary lactose intolerance is by far the most common, affecting an estimated 36% of American adults [10]. As babies and children, most digestive systems produce sufficient lactase so milk can be digested effectively during early development. However, as diets diversify with age, lactase production may gradually decline. For this reason, primary lactose intolerance typically develops during adolescence or adulthood [9].
• Secondary lactose intolerance - Secondary lactose intolerance results from damage or disruption to small intestine function. This could result from a physical injury, illness, or surgical procedure. Individuals with conditions such as celiac disease may experience lactose intolerance as a comorbidity due to damage affecting the small intestine. In some cases, treating the underlying condition may help improve lactose intolerance symptoms.
• Congenital lactose intolerance - Some infants are born lacking the enzymes needed to digest milk due to a rare genetic abnormality [3]. Both parents must pass on the associated genetic mutation for congenital lactose intolerance to develop, making this form of lactose intolerance extremely uncommon.

One common misconception about lactose malabsorption is that it’s rare. However, from a global perspective, as much as 68% of the world’s population may experience difficulty digesting milk without some degree of digestive discomfort [10].

If you regularly experience digestive symptoms after consuming dairy products, consider speaking with a healthcare professional. They can help determine whether lactose intolerance, a dairy allergy, or another digestive condition may be contributing to your symptoms and recommend appropriate testing or dietary modifications to support your health.

It’s not uncommon for people to confuse dairy allergies and lactose intolerance, but there are five crucial distinctions to be made between them:

1. Dairy allergies deal with the immune system, while lactose intolerance is a condition involving the digestive system.
2. Dairy allergies result from a hyperreactivity to milk proteins, while lactose intolerance results from an inability to deal with a sugar called lactose.
3. While dairy allergies primarily affect babies and present in infancy, lactose intolerance is remarkably common in adults worldwide.
4. Dairy allergies can be a medically serious condition, while lactose intolerance typically only leads to physical discomfort.
5. While it’s common to outgrow dairy allergies, the symptoms of lactose intolerance may persist indefinitely without proper management.

Comparing your symptoms and understanding your likelihood of being affected by dairy allergies or lactose intolerance is the first step in determining whether you may have either condition. The second is to undergo testing with a qualified healthcare provider.

Dairy allergy testing and treatment

Healthcare providers use three types of tests to confirm the existence of a dairy allergy [1]:

• Skin test - During a skin test, providers will administer a small amount of milk protein to the skin to assess whether it triggers an allergic reaction. It’s a safe, medically supervised procedure, and most children or people with a dairy allergy will only develop a small, localized hive on their skin.
• Blood test - Blood tests for dairy allergies evaluate the immune response to milk proteins. If an individual has a dairy allergy, their bloodstream usually exhibits high levels of IgE when exposed to milk.
• Oral exam - In some cases, skin and blood tests cannot sufficiently diagnose a dairy allergy. During an oral exam, you’ll consume small samples of food that may or may not contain milk-based ingredients while under medical supervision. If your immune system reacts to those containing dairy, you likely have an allergy.

Like any other food allergy, the single most important factor in dairy allergy treatment is to eliminate foods that trigger an allergic response.

That said, immune thresholds may differ from individual to individual. For instance, some people with a dairy allergy experience no symptoms after consuming fermented milk products (e.g., yogurt) or milk that has been exposed to high heat (e.g., bakery items) [1].

Most importantly, young children and adults who exhibit severe allergic reactions to milk must carry epinephrine to limit their likelihood of experiencing anaphylaxis if exposed to dairy. Keeping epinephrine dispensers (e.g., EpiPens) on hand—and knowing how to use them—is paramount for protecting against the worst outcomes of a dairy allergy.

Lactose intolerance testing and treatment

There are two commonly used testing approaches used to confirm lactose intolerance [11]:

• Breath test - A hydrogen breath test is an accessible, easy way to screen for lactose intolerance. Your healthcare provider will have you drink a substance containing lactose and subsequently take a breath sample. Then, they’ll examine the levels of hydrogen in your sample. If your hydrogen levels are high, you may have lactose intolerance.
• Blood test - Blood tests assess the amount of glucose in your bloodstream after you’ve consumed lactose. Typically, digesting lactose causes an uptick in blood glucose levels. If your glucose levels remain static, you may be lactose intolerant.

Triggers for lactose intolerance can be highly variable between individuals. In some cases, small amounts of dairy are tolerated well, or symptoms may improve by carefully introducing your digestive system to lactose-containing products [8].

If you suspect that dairy products or other foods may be contributing to digestive discomfort or other symptoms, consider speaking with a healthcare professional. They can help evaluate your symptoms, recommend appropriate testing, and guide you toward dietary strategies that support your long-term health and well-being.