Lactose intolerance is different from milk or dairy allergy. A dairy allergy involves an immune reaction by the body, whereas lactose intolerance is due to the inability to digest the sugars in milk products.

Lactose intolerance is when the body is unable to properly digest the sugars in milk. This can cause uncomfortable digestive symptoms. This differs from dairy allergies, which occur due to an immune response to the proteins in dairy products and can cause severe reactions.

As dairy products can both result in allergies and intolerances and may present with similar symptoms, some people may confuse the conditions. However, they are very different.

In this article, we will discuss the differences between lactose intolerance and dairy allergies.

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People can have different types of reactions to foods, where symptoms may occur due to either an allergic response, such as a food allergy, or an inability to properly digest certain foods, such as a food intolerance.

Dairy products can be responsible for both allergies and intolerances.

A dairy allergy, or milk allergy, occurs when the immune system overreacts to the presence of proteins in milk. However, lactose intolerance is not an allergy because it does not involve the immune system.

Instead, a person lacks an enzyme known as lactase, which breaks down a sugar — lactose — that naturally occurs in milk and dairy products, such as cheese and yogurt.

Dairy allergies

A cow’s milk allergy is the most common food allergy in infants and young children. However, people can be allergic to other types of milk, such as sheep, goat, and buffalo.

When a person with a dairy allergy encounters products containing dairy, it results in their immune system overreacting.

There are two types of dairy allergy: Immunoglobulin E (IgE)-mediated and non-IgE-mediated.

IgE refers to a type of antibody that the immune system may produce after recognizing a foreign substance. The immune system mistakenly determines that dairy proteins are harmful and responds by releasing chemicals, such as histamine.

This release of chemicals causes the symptoms of an allergic response. An IgE-mediated response typically occurs immediately.

A non-IgE-mediated response involves other components of the immune system rather than IgE. These reactions do not appear as quickly as IgE-mediated reactions and usually cause gastrointestinal symptoms such as vomiting, bloating, and diarrhea.

This is often why some people may confuse a non-IgE-mediated dairy allergy with lactose intolerance.

Lactose intolerance

A person with lactose intolerance does not have an allergy, but rather they cannot digest the sugars present in milk. This typically occurs due to lactose malabsorption. This term refers to the small intestine producing insufficient levels of lactase.

Estimates suggest that roughly 2 in 3 of the world’s population experience lactose malabsorption.

These low levels of lactase result in difficulty digesting or absorbing lactose, which leads to digestive symptoms such as bloating, diarrhea, and gas.

Possible causes of lactose intolerance include:

  • Lactase nonpersistence: This is when the intestine produces less lactase after infancy. Lactase levels get lower with age and a person may not show symptoms of intolerance until later childhood, adolescence, or adulthood.
  • Congenital lactase deficiency: This rare condition causes a person to produce little or no lactase from birth.
  • Injury: Damage to the small intestines, such as from Crohn’s or celiac disease, may cause a person to produce less lactase.
  • Premature birth: In some children born early, the small intestine may not produce enough lactase shortly after birth. However, it usually produces more as the baby gets older.

The main difference between lactose intolerance and dairy allergy is that one is an allergy and the other is an intolerance. An immune reaction causes dairy allergy, and a lack of the enzyme lactase causes lactose intolerance.

Other differences between lactose intolerance and milk allergy include the timing and severity of symptoms.

For example, a milk allergy most often appears in the first year of life, while lactose intolerance typically appears later. Furthermore, a severe allergic reaction to milk can be life threatening, whereas symptoms of lactose intolerance can be mild or more severe discomfort and pain.

IntoleranceIgE-mediated allergyNon-IgE-mediated allergy

Development
Typically appears later in life but can be present from birth.Usually present from birth and a person may outgrow the allergy.Usually present from birth and a person may outgrow the allergy.
OnsetSymptoms usually appear later.Symptoms appear soon after eating the food, usually within 2 hours.Symptoms may take up to 48 hours to develop.
AmountA person may be able to eat a very small quantity of dairy with no adverse reaction.The person cannot tolerate even small amounts of dairy they are allergic to. Exposure to even a tiny amount of the food can produce a severe reaction.Small amounts of the allergen will result in a response.
ExposureA reaction will occur only if the person consumes dairy.A reaction may occur if the person consumes a product with dairy. It may also occur if someone prepares food or drink in an environment that contains dairy.A reaction will also occur if a person consumes dairy or a food or drink item from an environment containing dairy.
EffectReactions can be extremely unpleasant but are rarely life threatening.Severe and potentially life threatening reactions that can include anaphylaxis (anaphylactic shock).Rarely life threatening as it is unlikely to result in anaphylaxis.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) advises that lactose intolerance may cause the following symptoms:

  • gas
  • bloating
  • diarrhea
  • nausea
  • vomiting
  • pain in the abdomen
  • rumbling or growling sounds in the stomach

Symptoms can be mild or severe, depending on how much lactose a person consumes.

Initially, a doctor will ask someone about their symptoms, family and medical history, and diet. Then, they may perform a physical examination, which may involve checking for other conditions that can cause similar symptoms.

Sometimes a doctor will ask the person to avoid consuming dairy products for a while to see if symptoms subside.

A few tests are available to help a doctor diagnose lactose intolerance.

A hydrogen breath test involves consuming a liquid that contains lactose and breathing into a balloon-like container every 30 minutes over a few hours. If a person begins to experience symptoms and their hydrogen breath level increases, this suggests lactose intolerance.

Alternatively, a doctor may also measure a person’s blood sugar level before and after consuming a lactose solution. If blood sugar levels do not rise, this may indicate lactose intolerance.

Treating and managing lactose intolerance may consist of the following:

  • dietary modification
  • lactase supplementation
  • treating an underlying condition in people with secondary lactase deficiency

Dietary modification

Some people may need to manage their diet to avoid symptoms. They may only need to limit the lactose they eat or drink, while others must avoid it altogether. The following foods and drinks can contain lactose:

  • milk
  • cream
  • butter
  • whey
  • yogurt
  • cheese
  • some bread and other baked goods
  • processed foods, such as breakfast cereals, flavored chips, and other snack foods
  • processed meats

Lactase supplements

Doctors may advise a person with lactose intolerance to try lactase supplements. These products contain the enzyme lactase and can help to break down lactose. Typically, a person will take a tablet before they consume any food or drink containing lactose or add lactase drops to milk.

However, lactase supplements may not be suitable for some people, such as young children or pregnant people. Therefore, a person should check with their doctor before trying them.

Lactose intolerance and dairy allergies are different. Lactose intolerance is not an allergy because it does not involve the immune system — it is an inability to digest lactose.

People with lactose intolerance do not produce enough lactase to digest sugars in milk products. Conversely, dairy allergies are a reaction by the body’s immune system to dairy proteins. Dairy allergies often cause more immediate symptoms and may be life threatening if someone has a severe reaction.

If a person has symptoms when they consume milk and dairy products, they should see a doctor. The doctor can assess if they have an allergy or intolerance and suggest suitable treatment and management strategies.