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

Medically reviewed on June 16, 2022 by Jordan Stachel, M.S., RDN, CPT. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Table of contents

• What is a dairy allergy?
• What is lactose intolerance?
• How to know if you have a dairy allergy vs. lactose intolerance
• Identify your food triggers with Everlywell
• Related content

For many people, food intolerance and food allergy are synonymous. In the case of dairy allergies and lactose intolerance, they are commonly conflated. But they involve two wholly different systems of the body—and, often, two entirely different segments of the population.

Dairy allergies are classified as an immune disorder, while lactose intolerance expressly pertains to the digestive system. Moreover, most dairy allergies primarily appear in infancy, but lactose intolerance commonly occurs in adulthood.

Marked differences aside, the two disorders are triggered by the same ingredient: milk. Knowing the unique traits of each condition and how to discover whether you may be affected is a critical first step in making empowered decisions about your diet and health.

What is a dairy allergy?

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 ensuring 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 their immune system to flood the body with histamines, a chemical responsible for the inflammatory reactions underlying sufferers’ allergic symptoms [6].

While the mechanisms behind dairy allergies are well understood, the root cause of their occurrence is not known. Researchers believe 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 with infants who are breastfed [2,3].

Fortunately, most babies and young children with dairy allergies outgrow their condition by adolescence [2]. Testing can be an essential component of dairy allergy diagnosis and treatment, enabling parents and loved ones to identify whether or not the disorder has receded with time.

What is lactose intolerance?

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 individuals’ ability to meet their daily vitamin D and calcium quotas. For this reason, it’s critical to identify whether you have the condition to 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 3 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 of our digestive systems produce sufficient lactase so that we can process our primary source of nutrition: milk. But as we get older and our diet diversifies, lactase production slows as our body comes to rely on other food sources. For this reason, primary lactose intolerance typically sets in 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 even surgical procedures. Individuals with celiac disease, for instance, are prone to structural damage to the small intestine and may experience lactose intolerance as a comorbidity of their primary condition. In some cases, treatment for underlying conditions may enable people with secondary lactose intolerance to overcome their symptoms.
• Congenital lactose intolerance - Some infants are born lacking the enzymes they need to digest milk due to a genetic abnormality [3]. Both parents must pass on a rare genetic mutation to develop congenital lactose intolerance, making congenital forms of lactose intolerance extremely uncommon.

One common misconception about lactose malabsorption is that it’s an exception rather than a norm. However, from a global perspective, as much as 68% of the world’s population cannot digest milk without some degree of digestive discomfort [10].

For people with a lactase deficiency, it can be frustrating to give up dairy-rich treats like delicious cheeses and summertime ice cream sundaes. Fortunately, testing for dairy sensitivity or a dairy allergy is a crucial first step in determining how to adapt gracefully to a diet that cares for your body’s unique needs.

How to know if you have a dairy allergy vs. lactose intolerance

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 systems and knowing your likelihood of being affected by dairy allergies or lactose intolerance is the first step in determining whether you have either condition. The second is to undergo testing.

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 heal by carefully introducing your digestive system to lactose-containing products [8].

For this reason, food sensitivity tests can be an important, comprehensive step in identifying unique triggers. The better you know which foods do (and don’t) sit well with your stomach, the more consciously—and confidently—you can design a diet that fits your life and tastes.

Identify your food triggers with Everlywell

If you’re wondering whether milk products may be triggering symptoms, Everlywell can help you make informed decisions about what foods to enjoy and which to limit. The Everlywell at-home Food Allergy Test measures your body’s immunoglobulin E (IgE) reactivity to common food allergens, including cow's milk.

Related content

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How to know if you have a food allergy

Food allergy, food sensitivity, and celiac disease: An expert explains the key differences and how to test

References

1. Milk allergy. Mayo Clinic. URL. Accessed June 16, 2022.

2. European Journal of Pediatrics. Cow’s milk allergy: evidence-based diagnosis and management for the practitioner. URL. Accessed June 16, 2022.

3. Differentiating milk allergy (IgE and non-IgE mediated) from lactose intolerance: understanding the underlying mechanisms and presentations. British Journal of General Practice. URL. Accessed June 16, 2022.

4. Cow Milk Allergy. StatPearls. URL. Accessed June 16, 2022.

5. Anaphylaxis. American Academy of Allergy Asthma & Immunology. URL. Accessed June 16, 2022.

6. Histamine: The Stuff Allergies are Made of. MedlinePlus. URL. Accessed June 16, 2022.

7. Lactose Intolerance. MedlinePlus. URL. Accessed June 16, 2022.

8. Lactose intolerance. Mayo Clinic. URL. Accessed June 16, 2022.

9. Lactose Intolerance. Johns Hopkins Medicine. URL. Accessed June 16, 2022.

10. Definition & Facts for Lactose Intolerance . National Institute of Diabetes and Digestive and Kidney Diseases. URL. Accessed June 16, 2022.

11. Lactose Tolerance Tests. MedlinePlus. URL. Accessed June 16, 2022.