Cow's milk is one of the most common allergy-causing foods in children, and it's the leading cause of allergic reactions in very young children. Milk allergy affects about 2 percent to 3 percent of infants worldwide, and its signs and symptoms can be serious enough to cause distress not just for an allergic child, but also for the child's family. The good news is that most children outgrow a milk allergy by age 2 or 3.
Signs and symptoms of milk allergy differ from person to person and occur within a few minutes to a few hours after ingesting milk. In some cases, reactions to a milk allergy develop after exposure to milk for an extended period of time. Rarely, infants have an allergic reaction to small amounts of cow's milk protein passed through their mother's breast milk.
Signs of a milk allergy that may occur immediately after consuming milk include:
Signs and symptoms that may take more time to develop include:
- Loose stools (which may contain blood or mucus)
- Abdominal cramps
- Coughing or wheezing
- Runny nose
- Skin rash
Milk allergy or milk intolerance?
It's important to differentiate a true milk allergy from milk protein intolerance or lactose intolerance. Unlike a milk allergy, intolerance doesn't involve the immune system. Milk intolerance causes different symptoms and requires different treatment than does a true milk allergy. Common signs and symptoms of milk protein or lactose intolerance include digestive problems, such as bloating, gas or diarrhea, after consuming milk.
Rarely, milk allergy can cause anaphylaxis, a life-threatening reaction that can constrict the airways and block breathing. If you or your child has a reaction to milk, tell your doctor about it no matter how mild the reaction may have been. Tests can help confirm a milk allergy, so you can take steps to avoid future and potentially worse reactions. Anaphylaxis is a medical emergency and requires treatment with an epinephrine (adrenaline) shot and a trip to the emergency room. Signs and symptoms start soon after consuming milk and can include:
- Constriction of airways, including a swollen throat that makes it difficult to breathe
- Shock, with a severe drop in blood pressure
- Rapid pulse
Dizziness, lightheadedness or loss of consciousness
What causes it?
All food allergies are caused by an immune system malfunction. Your immune system identifies certain milk proteins as harmful, triggering the production of immunoglobulin E (IgE) antibodies to neutralize the protein (allergen). The next time you come in contact with these proteins, these IgE antibodies recognize them and signal your immune system to release histamine and other chemicals. Histamine and other body chemicals cause a range of allergic signs and symptoms. Histamine is partly responsible for most allergic responses, including runny nose, itchy eyes, dry throat, rashes, hives, nausea, diarrhea, labored breathing and anaphylactic shock.
There are two types of protein in milk that can cause an allergic reaction:
- Casein, which is found in the solid part (curd) of milk that curdles
- Whey, which is found in the liquid part of milk that remains after milk curdles
You or your child may be allergic to only one milk protein or allergic to both casein and whey. These proteins are not only present in milk — but also are found in many processed foods. Certain foods contain both casein and whey; other foods contain only one allergy-causing milk protein.