Cow's milk allergy or lactose intolerance? Keys to understanding the differences

Many concerned parents consult a doctor when they notice their child experiencing discomfort after drinking milk: from crying and irritability to abdominal pain or diarrhea. When faced with these symptoms, a common question is whether the child may have a cow's milk allergy or lactose intolerance. Although the two are often confused, they are two different conditions, and it's important to learn to differentiate between them in order to address them appropriately.

Dr. Jesús González Pérez, a pediatrician at Quirónsalud Zaragoza Hospital , explains the differences between the two conditions on the website " School of Families ," highlighting the importance of recognizing their symptoms and consulting a pediatrician for a proper diagnosis.

In the case of cow's milk allergy , the problem isn't the milk sugar, but its proteins . The child's immune system reacts to these proteins as if they were a threat, triggering an allergic response. This allergy is especially common during the first year of life, especially when an artificial formula based on cow's milk is introduced after breastfeeding. Furthermore, as Dr. González Pérez points out, children allergic to cow's milk often also react to milk from other mammals, such as goat or sheep.

Symptoms may appear immediately , usually within the first hour after ingestion, or later , a few hours later. In immediate cases (mediated by immunoglobulin E or IgE), the signs are usually more striking: hives, skin rashes, cough, respiratory distress, vomiting, or even signs of a severe reaction. In late forms (not mediated by IgE), more common in young infants, digestive symptoms such as severe colic, persistent diarrhea, blood in the stool, vomiting, or food refusal predominate, and improvement may take days after discontinuing breast milk.

In both cases, if an allergic reaction is suspected, it is advisable to immediately stop consuming cow's milk and its derivatives and consult a pediatrician or pediatric allergist. Cow's milk protein allergies usually disappear over time: according to data from the Spanish Association of Pediatrics, most children outgrow them before the age of 5, and only a small percentage (around 15%) maintain their allergy into adulthood.

On the other hand, lactose intolerance has a completely different cause. In this case, it's not an allergy, but rather a difficulty digesting lactose, the natural sugar found in milk. This difficulty is due to a lack or decrease in an enzyme called lactase, which normally breaks down lactose in the small intestine. When lactose isn't digested properly, it passes into the large intestine where it ferments, producing gas, bloating, abdominal pain, and acidic or explosive diarrhea.

Dr. González Pérez points out that this intolerance can appear temporarily, for example, after gastroenteritis, or be associated with other intestinal diseases such as celiac disease. It can also be a persistent condition, especially in older children or adolescents, when lactase production naturally decreases with age (called primary intolerance).

Unlike allergies, lactose intolerance does not entail a risk of severe reaction or respiratory or skin symptoms, and does not require avoiding other animal products such as goat's milk. Symptoms are exclusively digestive and generally disappear when lactose is reduced or eliminated from the diet.

To guide the diagnosis, Dr. González Pérez recommends recording the foods the child has eaten and any symptoms that have occurred, and bringing this information to the pediatrician. In some cases, specific tests such as a food challenge test, blood tests, or breath tests will be necessary. It is also very useful to learn how to read food labels, as some manufactured products may contain milk, casein, or lactose without it being obvious to the naked eye.

Finally, there are safe and nutritious alternatives for children with these conditions. In cases of allergies, the pediatrician may recommend special formulas such as extensively hydrolyzed or even elemental formulas. In cases of lactose intolerance, lactose-free milks can be used, and in many cases, small amounts of dairy can even be maintained if they are well tolerated.