Milk contains two main groups of proteins: - Casein, about 80% - Whey proteins, about 20% When milk is used to make cheese: - Casein forms the solid curds. - Whey remains in the liquid. That liquid is called whey.

Why Can Whey Proteins Trigger an Allergic Reaction?

Q: Why Is β-lactoglobulin Important?

One of the best known whey proteins is β-lactoglobulin. Interestingly, human breast milk does not naturally contain β-lactoglobulin. It is found in the milk of: - Cows - Goats - Sheep Because it is a protein that humans are not naturally exposed to through breast milk, it can act as an allergen in susceptible individuals. However, being a foreign protein does not automatically make it allergenic. Most people consume β-lactoglobulin throughout their lives without any problems. An allergy develops only when the immune system loses, or never develops, tolerance to that protein.

Q: Why Doesn't Everyone Develop a Whey Allergy?

Most people's immune systems develop oral tolerance. When they eat milk proteins, the immune system learns that these proteins are harmless food and does not react to them. In children with a cow milk allergy, this process of tolerance has been disrupted. Instead of recognizing the proteins as safe, the immune system treats them as a threat.

The Worldly Goat

Jul 15

3 min read

Whey proteins are nutritious proteins found naturally in milk. For most people, they are completely harmless. However, in some people with a cow milk allergy, the immune system mistakenly identifies these proteins as dangerous and launches an allergic reaction.

Let's explore why this happens.

What Is Whey?

Milk contains two main groups of proteins:

Casein, about 80%
Whey proteins, about 20%

When milk is used to make cheese:

Casein forms the solid curds.
Whey remains in the liquid.

That liquid is called whey.

Which Proteins Are Found in Whey?

Whey is not a single protein. It is a mixture of several different proteins, including:

β-lactoglobulin
α-lactalbumin
Bovine serum albumin (BSA)
Immunoglobulins
Lactoferrin

Each protein has its own unique shape and structure.

How Does the Immune System Recognize Whey Proteins?

The immune system does not recognize an entire protein all at once.

Instead, it recognizes tiny regions on the surface of the protein called epitopes.

These small regions act like identification markers that antibodies can bind to.

In someone with an IgE-mediated cow milk allergy, the immune system has produced IgE antibodies that recognize specific epitopes on one or more milk proteins.

When those antibodies attach to the protein, they activate immune cells called mast cells and basophils.

These cells release chemicals including:

Histamine
Leukotrienes
Prostaglandins

These chemicals cause the symptoms of an allergic reaction.

Why Is β-lactoglobulin Important?

One of the best known whey proteins is β-lactoglobulin.

Interestingly, human breast milk does not naturally contain β-lactoglobulin.

It is found in the milk of:

Cows
Goats
Sheep

Because it is a protein that humans are not naturally exposed to through breast milk, it can act as an allergen in susceptible individuals.

However, being a foreign protein does not automatically make it allergenic. Most people consume β-lactoglobulin throughout their lives without any problems. An allergy develops only when the immune system loses, or never develops, tolerance to that protein.

Why Do People React to Different Milk Proteins?

Every person's immune system is unique.

One child may produce IgE antibodies mainly against β-lactoglobulin.

Another may react mostly to casein.

Others may react to several milk proteins at the same time.

This is why allergy test results can vary from one person to another.

Does Heating Reduce the Allergy?

Sometimes.

Whey proteins are generally more sensitive to heat than casein proteins.

Heating can change the shape of some whey proteins, which may alter the epitopes that IgE antibodies recognize.

As a result, some children with a cow milk allergy can tolerate extensively baked milk in foods such as muffins or cakes.

However, heating does not remove all allergenic proteins, and many children still react to baked milk. Whether baked milk is safe should always be determined by an allergy specialist.

Why Doesn't Everyone Develop a Whey Allergy?

Most people's immune systems develop oral tolerance.

When they eat milk proteins, the immune system learns that these proteins are harmless food and does not react to them.

In children with a cow milk allergy, this process of tolerance has been disrupted. Instead of recognizing the proteins as safe, the immune system treats them as a threat.

An Interesting Fact

About 80 to 90 percent of children with a cow milk allergy react to more than one milk protein. Many are allergic to both casein and one or more whey proteins. This is why removing only whey or only casein is usually not enough to make cow milk safe for someone with a diagnosed milk allergy.

Key Takeaway

Whey proteins can trigger an allergic reaction because the immune system mistakenly recognizes specific epitopes on those proteins as dangerous. In people with an IgE-mediated cow milk allergy, IgE antibodies bind to these epitopes and activate immune cells, which release histamine and other inflammatory chemicals. The proteins themselves are nutritious and harmless for most people. The allergic reaction occurs because the immune system has learned to respond to them inappropriately.