Sensitization or allergy? What’s the difference?

Bearded man looking puzzled about the difference between being sensitized and having an allergy. He should read our guide

Have you heard of the term sensitization? It’s especially used in connection with allergy tests that identify allergy triggers by detecting your sensitization to specific allergens. But what is sensitization and how is it different to allergy? In this article we’re going to explain the process of how allergy develops. We’ll also explain the difference between sensitization and allergy, and the role sensitization plays in allergy testing.

What are allergies?

To understand sensitization we need to take a closer look at the mechanics of allergy. Allergies are an overreaction of your immune system in response to a substance that is normally harmless.

Substances that cause allergic reactions are called allergens. If you have allergy your immune system mistakes the allergen as a threat and overreacts to try to protect you.

What happens when you have an allergic reaction?

In an allergic reaction to substances such as pollen, house dust mites, certain foods or insect stings, the immune system produces antibodies called Immunoglobulin E (IgE) specific to the trigger it’s trying to fight.

These IgE antibodies tell other cells to release certain chemicals, including histamine. And it’s those chemicals that cause the annoying and sometimes even life-threatening allergy symptoms.


Sensitization is the first step in developing an allergy. Being sensitized is not the same as having an allergy.

What is sensitization then?

Sensitization is the first step in developing an allergy.

Allergic reactions don’t happen the first time you encounter an allergen. To begin with, your immune system has to register the allergen. For example, by being stung by a bee. Then your immune system memorizes the particular structure of the allergen so that it can produce specific IgE antibodies in defense. This process is called sensitization.

You’re sensitized when you have specific IgE antibodies in your blood. Once you have been sensitized to a particular allergen, your body will produce IgE every time you encounter that allergen again.

When does sensitization usually develop?

Sensitization happens early in childhood and without you being aware of it. The production of IgE begins when a baby is still in the womb. Becoming sensitized to foods like eggs and milk can happen when a baby is a few weeks to a few months old. Sensitization to other allergens in the environment such as pollen, house dust mites and pets takes a bit more time to develop and usually happens in the pre-school or early school years.

Multiples allergies?

Can you be sensitized to more than one allergen?

Sensitization to more than one allergen is common, affecting 10% of the general population and more than half the people with allergy. Being sensitized to just one allergen is sometimes called monosensitization. But you can also be sensitized to multiple allergens. This is known as polysensitization.

No allergy without symptoms

Sensitization is not the same as allergy. Sensitization does not always lead to symptoms, but symptoms do not develop without sensitization. In other words, you can be sensitized without being allergic, but you can’t be allergic without being sensitized first.

Sensitized but not allergic

Some people have developed IgE antibodies for a specific allergen but when they come into contact with that trigger again, they don’t experience any allergy symptoms. These people are sensitized but not allergic. In other words, their immune system is sensitive to an allergen or allergens, but they don’t experience any symptoms of allergy.

Sensitized and allergic

For other people, when they are re-exposed to the allergen, they experience allergy symptoms. These people are both sensitized and allergic. Their immune system is sensitive to an allergen or allergens, and this causes symptoms of allergy.

What is allergic rhinitis?

What is allergic rhinitis?

Why are some people just sensitized and others allergic?

We aren’t sure why some people stop at sensitization and others progress to allergy. Our immune systems are highly complex and not all processes and mechanisms are fully understood yet.

We do know that you are more likely to develop an allergy if other members of your family also have allergy. This doesn’t mean that you inherit a particular allergy, it means you may inherit the tendency towards having allergy. But there’s always an exception, some people have allergies even if no family member does.

Allergy tests show your sensitization to specific allergens

Because it’s possible to detect sensitization, it can be a useful tool for identifying potential allergy triggers. Testing for IgE can give you an indication of your sensitization to specific allergens.

So, results of a test for sensitization can be a first step to finding out if you have an allergy.

It’s important to remember though that an accurate diagnosis of allergy requires both a test and a consultation with your health care provider. Your medical history is the fundamental link between your allergy test results and being diagnosed with allergy. Only a health care provider can give you a diagnosis of allergy and access to the whole range of allergy management options.

Find a doctor search icon
Find a doctor

Need help to find a doctor’s office?

Share your story

If you've read all the way to the end of this article, thank you. And we'd love to know what you think. Are you considering taking a test for allergy? Have you already been tested for allergy? Has knowing what you're allergic to made a difference for you? Head over to our Facebook page or email us and share your story.

klarify takes allergy science and makes it simple, and we have rigorous process for doing this. We use up-to-date and authoritative sources of information. Medical experts review our content before we share it with you. They and the klarify editorial team strive to be accurate, thorough, clear and objective at all times. Our editorial policy explains exactly how we do this.