Lactase Deficiency or Allergy: Similar Symptoms, Different Nature

28 de octubre de 2025

3 min de lectura

Lactase deficiency is often mistaken for an allergy to milk protein and vice versa. The confusion arises from the similarity of symptoms. But the nature of these pathologies is different: lactase deficiency is a digestive disorder, and milk allergy is an immune problem. Let's take a closer look at both of these—how they differ and what type of medical help to seek if necessary.

Puntos clave

Lactase deficiency is often mistaken for an allergy to milk protein and vice versa.
What is lactase deficiency?
Types of lactase deficiency

Para quién es

Personas que exploran Alergia a través de lactase intolerance, alergia.

Por qué importa

Este artículo te ayuda a orientarte rápidamente y luego avanzar a una colección o serie si quieres seguir profundizando.

Autor del artículo

Dr. Angelique

Pediatra

What is lactase deficiency?

Lactose (milk sugar) is a two-component carbohydrate that makes up 99 percent of all carbohydrates in dairy products. It activates the nervous system and is the main source of energy. In the intestines, the sugar lactose is digested by the enzyme lactase. In the case of lactase deficiency, the body simply doesn’t absorb the lactose. It enters the large intestine in a concentrated and undigested form. The most obvious symptoms of lactase deficiency are loose stools and flatulence.

Types of lactase deficiency

Lactase deficiency can be inborn, which affects 5–6 percent of people at the time of birth. Their intestinal mucosa is not damaged, but the enzyme is too small.

Important! For any kind of malfunction of the baby's intestines, you should not give up breastfeeding, as breast milk contains antibodies that create the child's immunity along with nutrients and vitamins.

Lactase deficiency can also be acquired as a child or an adult. If the intestinal mucosa is damaged, the production of lactase is disrupted. The content of the enzyme in the body decreases, and lactase deficiency occurs.

Acquired lactase deficiency can be caused by natural involution of enzyme activity, infections (rotavirus, giardiasis, etc.), Crohn's disease, pancreatitis, resection of the small intestine, lactose overload, or radiation damage.

What tests do you need to take?

The following laboratory tests are required to diagnose lactase deficiency:

Stool analysis—complete chorogram and biochemical analysis.
A blood test to determine lactose load.
Biopsy of the small intestine mucosa—gives 100 percent reliability of the diagnosis.
Respiratory tests of exhaled air to determine the level of hydrogen.
Genetic tests.

What doctor should you consult?

Lactase deficiency is a clinical condition that is caused by bowel problems. Therefore, you need to consult a gastroenterologist.

Milk protein allergy

Milk allergy occurs when a person's immune system perceives milk protein as a dangerous enemy and produces antibodies that are converted into histamine, a substance that causes allergies. An allergic reaction to milk protein can be mild, or a strong allergic reaction can be very dangerous.

Allergies, as a rule, appear quite quickly after ingestion of milk and dairy products—from a few minutes to an hour. Typical symptoms include skin irritation, eczema, nausea, abdominal pain, diarrhea, wheezing, runny nose, cough, and watery eyes.

What tests do you need to take?

If you suspect an allergy, then you should take the following tests:

General analysis of urine and blood to check for increased content of protein and leukocytes.

Blood biochemistry—allows you to determine an allergic reaction by an increased number of immune complexes.

Analysis for antibodies and lymphocytes sensitive to milk proteins. Blood immunogram to determine the ratio of immune complexes and their specificities.

Skin scarification tests or "allergy tests"—skin tests for suspected allergies.

In some cases, tests are carried out in a hospital through a provocative method in which the patient is given the suspected allergen in a concentrated form and the symptoms are recorded.

What doctor should you consult?

People who are allergic to milk protein should be seen by an allergist and avoid dairy products.

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