What Is Milk Allergy?

When someone has a milk allergy, the body's immune system, which normally fights infections, overreacts to proteins in milk. If the person drinks or eats a product that contains milk, the body thinks these proteins are harmful invaders. The immune system responds by working very hard to fight off the invader. This causes an allergic reaction.

Milk is among the most common foods that cause allergic reactions. Some kids with a milk allergy outgrow it as they get older.

What Happens in a Milk Allergy?

People who are allergic to milk react to one or more of the proteins in it. Some people are allergic to casein (KAY-seen) protein and some are allergic to whey (WAY) protein. Some people are allergic to both casein and whey.

When a person with a milk allergy eats these proteins, the body releases chemicals like histamine. This can cause symptoms like:

• wheezing
• trouble breathing
• coughing
• hoarseness
• throat tightness
• belly pain
• vomiting
• diarrhea
• itchy, watery, or swollen eyes
• hives
• swelling
• a drop in blood pressure, causing lightheadedness or loss of consciousness

Allergic reactions to milk can vary. Sometimes the same person can react differently at different times. Some reactions to milk are mild and involve only one part of the body, like hives on the skin. But even when someone has had only a mild reaction in the past, the next reaction can be serious.

Milk allergies can cause a severe reaction called anaphylaxis. Anaphylaxis can begin with some of the same symptoms as a less severe reaction, but can quickly get worse. The person may have trouble breathing or pass out. More than one part of the body might be involved. Anaphylaxis that isn't treated can be life-threatening.

Milk allergy is often confused with lactose intolerance because it can cause some of the same symptoms, like belly pain or diarrhea. While lactose intolerance can upset someone’s digestive system, it can’t cause a life-threatening reaction the way that a milk allergy can.

How Is a Milk Allergy Diagnosed?

If your child might have a milk allergy, the doctor may want you to go to an allergist or allergy specialist for more testing. They will ask about how often the reaction happens, the time it takes between when your child eats a particular food and the start of the symptoms, and whether any family members have allergies or conditions like eczema and asthma.

The allergy specialist may do a skin test. This involves placing tiny amounts of milk protein on your child’s forearm or back, making a small scratch or prick on the skin, and waiting to see if a reddish, raised spot forms. If so, it may indicate a milk allergy.

Your child may need to stop taking some medicines (such as over-the-counter antihistamines) 5 to 7 days before the skin test because they can affect the results. Check with the allergist's office if you’re not sure about what medicines to stop or for how long.

An allergist might do a blood test as well as skin testing. A small blood sample will go to a lab for testing. The lab checks the blood for IgE antibodies to specific foods. If your child’s blood has enough IgE antibodies to milk, a milk allergy is very likely.

If the results of the skin and blood tests are still unclear, though, an allergist might do something called a food challenge. During this test, your child will get slowly increasing amounts of milk while the doctor watches for symptoms.

How Is an Allergic Reaction to Milk Treated?

Kids with a milk allergy should always carry two epinephrine auto-injectors in case of a severe reaction. An epinephrine auto-injector is a prescription medicine that comes in a small, easy-to-carry container. It's easy to use. Your doctor will show you how. Always have two auto injectors with your child in case one doesn't work or they need a second dose.

The doctor can also give you an allergy action plan, which helps you prepare for, recognize, and treat an allergic reaction. Share the plan with anyone else who needs to know, such as other caregivers, babysitters, relatives, school officials, and coaches. Also consider having your child wear a medical alert bracelet.

Every second counts in an allergic reaction. If your child has serious allergic symptoms, like trouble breathing or throat tightness, use the epinephrine auto-injector right away. Also use it right away if your child’s symptoms involve two different parts of the body, like hives with vomiting. Then call 911 and have them take your child to the emergency room. This is because even if the worst seems to have passed, a second wave of serious symptoms can happen.

What Else Should I Know?

Kids with a milk allergy must not eat or drink any products that contain milk or milk proteins.

Be sure to read food labels carefully and teach your child to do the same. Milk and milk proteins can be in unexpected places, such as processed lunchmeats, salad dressings, baked goods, chocolate, and crackers. Even foods that say “non-dairy” still may contain milk protein. 

One thing that might not show up on a label is cross-contamination risk. This can happen if a manufacturer uses the same equipment to grind lots of different foods, for example. Some companies put statements on their labels about the risk of cross-contamination, like: "May contain milk," "Processed in a facility that also processes milk," or "Manufactured on equipment also used for milk." Your child should avoid products that have these kinds of alerts.

But companies are not required to put cross-contamination alerts on a food label. So it's best to contact the company to see if a product might have come in contact with milk. You may be able to get this information from a company website. If not, contact the company and ask.