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Milk Allergy vs. Lactose Intolerance: What’s the Difference?

Milk Allergy vs. Lactose Intolerance: What’s the Difference?

Updated 14 April 2020

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Reviewed by Tanya Tantry, MD, Obstetrician & Gynecologist, Medical Consultant at Flo

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If you’ve noticed your baby has an unusual reaction to milk and dairy, it’s important to find out whether it’s lactose intolerance or a milk allergy. These two conditions sound like the same thing, but they’re entirely different and are treated accordingly.

Lactose intolerance vs. a milk allergy: symptoms

A milk allergy, or more specifically cow’s milk allergy (CMA), is the immune system’s abnormal reaction to cow’s milk and related dairy products. Milk from sheep, goats, or other mammals can also sometimes cause an allergic reaction.

On the other hand, lactose intolerance is when there’s not enough of the digestive enzyme lactase to break down milk sugars. Let’s find out the difference between a milk allergy and lactose intolerance, their symptoms, causes, and how to tell which one your baby might have.

A few symptoms that a milk allergy and lactose intolerance have in common are bloating, gas, and indigestion. There are also some key symptoms that set them apart. Symptoms of a milk allergy can be more severe and require medical treatment. Let’s find out more about the symptoms for each condition.

Milk allergy symptoms:

If your baby has a milk allergy, you will see symptoms within minutes, or sometimes a couple hours, after they eat or drink dairy. You might notice a few or all of these symptoms:

Immediate symptoms (within minutes):

wheezing and difficulty breathing
hives
itching
nausea
swelling of lips and face
trouble swallowing
tightness in throat

Symptoms that may take more time to appear:

loose stools or diarrhea, which may contain blood
abdominal cramps
a runny nose
watery eyes
colic

Lactose intolerance symptoms:

Symptoms of lactose intolerance take longer to arrive than for a milk allergy, sometimes showing up about 30 minutes or a couple of hours later. The severity of the symptoms depends on the amount of milk your baby drank. Typical symptoms of lactose intolerance are:

bloating
gas
diarrhea
abdominal cramps and pain
nausea, sometimes vomiting

Difference between lactose intolerance and a milk allergy: causes

There are important differences in the causes of lactose intolerance and a milk allergy. It’s important to know how the body reacts to both conditions. Let’s look at the causes of the two conditions and their key differences.

Age of onset: Milk allergies are most commonly seen in children under the age of five, although you can develop it at any age. Studies show that up to 80% of children with a milk allergy are no longer allergic by the age of five. On the other hand, lactose intolerance usually occurs in adolescents and adults. This is because our bodies produce less lactase as we get older, making it harder to digest milk and dairy.
Immune response vs. digestion intolerance: While a milk allergy is an immune system response, lactose intolerance is a food intolerance and does not involve the immune system at all.
Cause of milk allergy vs. lactose intolerance: Milk allergies happen when the body has allergic antibodies against a protein found in cow’s milk. Lactose intolerance, on the other hand, happens because of a lack of the enzyme lactase, which makes it hard to digest milk and dairy products.
The severity of symptoms: Milk allergies are the third most common cause of anaphylaxis, when the body’s airways become constricted and block breathing. If you notice severe symptoms of an allergic reaction or anaphylaxis, seek medical treatment as soon as possible. Symptoms of lactose intolerance are uncomfortable but typically not as severe.

Can infants have lactose intolerance or a milk allergy?

CMA is more commonly seen in infants, though it is possible to develop at any age. A milk allergy is one of the most commonly found allergies in infants and young children. About 80% of milk allergies disappear by the time the child reaches the age of five.

Lactose intolerance is not commonly found in infants, though it is possible. Children can also develop a temporary lactose intolerance after a bout of diarrhea or an infection. In these cases, the lactose intolerance usually clears up in a couple of weeks.

Lactose intolerance versus a milk allergy: breastfeeding

It’s important to note that when we talk about milk allergies, we’re usually talking about cow’s milk. It’s rare for babies to be allergic or have an intolerance to breast milk. It is possible for babies to be allergic to something the mother ate that made its way into the breast milk, though. If your baby has a stuffy nose, watery eyes, and/or loose stools, your doctor can help you determine the cause.

Breast milk allergy in babies: With the exception of very rare genetic disorders, babies are not allergic to breast milk. However, it is possible for your baby to be allergic to food or medicine that you took that turns up in breast milk. The usual suspects are dairy, peanut, and soy products. In the case of dairy products, babies might be allergic to whey or casein, two types of protein found in cow’s milk. If you’ve consumed cow’s milk and your baby has CMA, they will get watery eyes, colic, a stuffy nose, and/or diarrhea after breastfeeding. You can solve the problem and resolve any milk allergy symptoms by avoiding dairy products.

Lactose intolerance to breast milk in babies: Lactose intolerance is the inability to digest lactose, a naturally occurring sugar found in milk. Primary, or “true,” lactose intolerance in babies is extremely rare and could be the result of an underlying genetic disorder. True lactose intolerance in babies is a serious condition and requires immediate medical intervention.

Babies can develop secondary, or temporary, lactose intolerance as a result of damaged intestinal lining or a bowel infection. In these cases, the lactose intolerance will disappear once the infection clears up. Unless your doctor tells you otherwise, you can usually continue breastfeeding. If your baby has a condition that requires special care, your doctor will recommend a diet to keep them healthy and happy.

Despite having some similar symptoms, a milk allergy and lactose intolerance are two very different conditions. A milk allergy is an abnormal immune response to proteins found in cow’s milk (sometimes goat or soy milk). Lactose intolerance happens when there’s not enough lactase to break down lactose, a naturally found sugar in milk. A milk allergy can cause rapid and severe symptoms such as shortness of breath and tongue swelling, requiring immediate medical help.

CMA is most commonly found in babies, while lactose intolerance typically appears in adolescents and adults. If your baby is showing an abnormal reaction to milk — watery eyes, stuffy nose, and diarrhea — something in your diet (food or medicine taken while breastfeeding) might be causing it. Your doctor can help you find out whether it’s a milk allergy or lactose intolerance, and the appropriate treatment needed. Read our handy guide on the most frequently asked questions on newborns for more information about your baby’s habits, needs, and more.