Understanding multiple allergies and the symptom threshold

If you’ve ever experienced allergy symptoms, you know how they can impact your quality of life. The sneezing, itchy eyes, runny nose or even a rash — these symptoms can disrupt your daily activities or cause you to skip opportunities to be outdoors. At the very least, they involve buying lots of tissues and always having them at the ready.

But do you know what’s actually driving your symptoms? Allergies can be complex conditions. Sometimes people are allergic to only one allergen, but often, people are allergic to multiple allergens. In fact, up to 80% of people with allergies are reacting to multiple allergens.¹ And it’s not just seasonal triggers; indoor allergens like dust mites or pet dander are around us all year long.

When you’re exposed to multiple allergic triggers, it can cause you to pass the “symptom threshold,” the point at which your body reacts by developing symptoms to those allergens. That’s why it's important to know your particular triggers so you can minimize your exposure and keep your symptoms under control. Let’s take a closer look at the symptom threshold and how to avoid it.

What is the symptom threshold?

The symptom threshold is the level of allergen exposure when symptoms appear. Essentially, it’s when your exposure to allergens is enough that your immune system starts responding with sneezing, coughing, itchy eyes and other physical symptoms.

One way to picture the symptom threshold is to imagine an empty glass — it starts to fill when you’re exposed to allergens you are allergic to. For example, you are exposed to dust mites, then it gets fuller when you encounter birch pollen, and when you’re exposed to pet dander too, it overflows. That’s the point when your symptoms begin.

Keep in mind that everyone’s symptom threshold is different. It depends on immune system sensitivity and the number of allergens present.² Understanding these factors can help you better anticipate and manage your symptoms.

Why don't I have symptoms all the time? 

Everyone has their own unique combination of allergic triggers and not all of them are obvious. You may be sensitized to several allergen sources, but your sensitization may not be enough to trigger symptoms when you’re exposed to just a small amount of the allergen or to only one allergen at a time.² But when you encounter multiple allergic triggers at the same time, they can add up, and you may start experiencing symptoms, such as itchy eyes or a runny nose.²

If one or more of your triggers is a seasonal allergy such as tree pollen or grass pollen, your symptoms may appear only at times of the year when that pollen is in the air. Trees, grasses and weeds, like ragweed, all pollinate at various times, so you may not experience symptoms until your particular seasonal trigger gets added to that imaginary glass on top of your year-round triggers like mold or dust mites.

How to manage your allergy symptoms

The first step to managing your symptoms is to understand your triggers. Your healthcare provider can order a specific IgE blood test that, along with your medical history, can help identify which allergen or allergens you’re reacting to. Once you know if you have multiple allergies and what your triggers are, you can minimize your exposure to them to lessen or eliminate your symptoms. For example:

Perennial indoor allergens

These are allergens that we’re exposed to all year round, as opposed to pollen that is only present in certain seasons. Indoor allergens include mold, pet dander and dust mites.  Dust mite allergens in particular are very common — nearly half (47%) of patients in one study were sensitized to dust mites.³

If you’re sensitized to multiple perennial indoor allergens, you may experience symptoms when concentrations of these indoor triggers reach your symptom threshold. Or, you could have a low-level allergy to one or multiple indoor allergens and experience little to no symptoms for much of the year.

Perennial indoor and seasonal outdoor allergies

If you have a seasonal allergy as well, you may have symptoms flare up when that outdoor trigger is present. Let’s say you’re allergic to dust mites and mold, but you don’t experience symptoms. However, you also have sensitization to grass pollen, so during the summer when grass pollen counts are at their highest, your symptoms appear because that trigger pushed you past your symptom threshold.⁴

You may think you have just a seasonal allergy because your symptoms only become an issue in summer when grass pollen is present. Without more comprehensive testing, you wouldn’t know about the dust mite and mold sensitization that are also playing a role in your symptoms.

Reduced exposure to allergens:

our best defense against your allergy symptoms is to know what’s causing them and to avoid those triggers. This doesn’t necessarily mean you’ll have to cut everything you’re allergic to out of your life. You'll just have to reduce your exposure enough to get below your symptom threshold.

If we return to our example above, knowing you’re allergic to dust mites, mold and grasses means you can take actions such as getting dust mite covers for your bedding to help reduce exposure to that trigger. It also means that in summer when grass pollen is high, you can keep your windows closed and make sure to shower and change clothes before getting into bed. This reduces the chance of pollen following you from outside into your sleeping space.

You can find specific exposure reduction strategies for various allergens at the bottom of all our allergen fact sheets. For example:

• Dust mites
• Cat dander
• Dog dander
• Tree pollen
• Grass pollen

Specific IgE blood testing is, well, specific enough that it can help identify which species of a tree, grass or weed that you’re reacting to, and that knowledge can make all the difference. Awareness of your particular triggers allows you to take steps to avoid them, and thereby reduce the impact of allergy symptoms on your quality of life.