This post was written in response to a question from TheScientificParent.org reader Salima, who received confusing information from her doctor and pharmacist about kids and allergies.
As a pediatric allergist, I see children of all ages presenting with a range of different symptoms, especially runny noses, cough, and rashes. As a parent, I see my children exhibit these same symptoms pretty much all the time. These are very common symptoms in children of all ages and often occur when allergies are present. However, they don’t always mean that allergies are present. Confused? Don’t worry – you’re not alone.
Parents often tell me they were also told that even though “it must be allergies” that allergy testing could not be performed until children are two, or three, even five years old. This is a common misperception and it’s never made any sense to me. Why can you diagnose a child with allergies but then tell parents that testing is not reliable until they are a certain age? Not only is this frustrating to parents, but it’s also incorrect. Hopefully this article will clarify many of the common misconceptions regarding allergy diagnosis and testing.
What is an allergy?
I get very picky about details. In regards to defining what is and is not an allergy, the details are extremely important. Details regarding the timing and type of symptoms can make a huge difference in deciding which diagnoses to consider. Details about family history, environmental exposures, and previous treatments are also very important. I liken my job to that of a detective – I ask lots of questions, gather evidence, and then try to connect the dots to arrive at a final conclusion.
Age is very important as inhalant allergies to indoor allergens such as pet dander and dust mites typically don’t begin until 12 months of age. Allergies to seasonal pollen don’t typically being until 2 years old at the earliest, and more commonly around age 3. That’s how I knew my son’s everlasting runny nose at 6 months old was due to daycare crud…and not allergies. When my two-year-old daughter developed a red, itchy rash on her abdomen and legs for 10 days, I knew it wasn’t due to allergies based upon the appearance, lack of associated trigger, and duration of symptoms.
An allergy is when the body’s immune system forms an antibody response against an allergen. Allergens are proteins that come from pollen, foods, medications, animals, and insects. Someone can develop immediate allergic reactions (caused by Immunoglobulin E, or IgE) or delayed immunologic reactions. Regardless, when someone forms an immune response against a specific allergen, they will then experience reproducible symptoms every time they are exposed to that allergen.
When IgE antibodies are formed against specific allergens, they attach themselves to allergy cells called mast cells. Mast cells are present everywhere throughout the body, including the skin, respiratory and gastrointestinal tract, and even in the tongue. When people encounter their specific allergens, the IgE antibodies unlock the mast cells, releasing their contents. Histamine is a chemical present inside mast cells that is immediately released. Other immune signals are also released throughout the body, which then recruit additional inflammatory chemicals to join in the ensuing allergy party.
Histamine is important for a few reasons. First and foremost, histamine can cause all of the symptoms of an allergic reaction. Symptoms differ based upon the part of the body but often include itching, red raised welts called hives, swelling (skin), wheezing and coughing (lungs), nausea, vomiting, or diarrhea (GI tract) and can even cause loss of consciousness from low blood pressure or lack of oxygen reaching the brain (blood vessels).
Not every allergic reaction will cause all of these symptoms, but histamine is the main player involved. Food allergies typically cause more severe symptoms than inhalant allergies (pollen, pet dander), which mainly cause itching of the nose and eyes, sneezing, runny/stuffy nose and cough. Antihistamine medications are often a mainstay of treatment for inhalant allergies as they can block the effects of histamine inside the body, thus reducing symptom severity.
What does an allergy test involve?
Specific IgE towards allergens can be detected by two different testing techniques. Skin prick testing is performed in the office setting and involves placing a tiny drop of liquid allergen onto the skin (usually the back, but can also use the forearm), followed by a prick through the top layer of the skin. This introduces the allergen to the mast cells. If IgE towards that allergen is present and attached to mast cells, they will immediately release histamine. This causes a hive to develop at the site of the prick (severe or systemic reactions to this test are exceptionally rare). The other test is a blood test, which measures the level of circulating IgE towards specific allergens.
How accurate are allergy tests?
Both tests have very high negative predictive values but poor positive predictive values. Thus, these are not good screening tests. The clinical history (details, again) regarding symptoms, timing, specific triggers, etc. is critical in guiding whether allergy tests should be performed in the first place and how they should be interpreted.
Neither test can predict the severity of an allergic reaction. In general, the larger the size of the skin prick test or higher IgE level in the blood, the more likely it is that IgE mediated allergies are present. Severity of allergies can be predicted based upon prior symptoms, but may also worsen over time.
Why was I told that allergy tests cannot be performed until a certain age?
This is a huge myth, likely based upon outdated and incomplete understanding of the developing immune system. Quite simply, if you are old enough to produce an IgE-mediated allergic response, then you are old enough to have a test that detects specific IgE towards that allergen.
Allergy tests are often negative in young infants and children, but that is typically due to testing being performed for symptoms not caused by IgE mediated allergies. For example, I see many children with chronic gastrointestinal symptoms such as heartburn, constipation, or diarrhea that are referred for allergy testing. It is extremely rare for IgE food allergies, which cause immediate onset hives, swelling, and/or anaphylaxis, to result in chronic symptoms such as this; therefore, any IgE testing for non-IgE mediated symptoms will be negative…and unnecessary.
Why did my child’s doctor decide to treat for allergies instead of immediately refer them for allergy testing?
Environmental allergies are very common in children, affecting 20-30% of some populations. Primary care doctors are well versed in treating allergies given how often they see them in their patients. Treatment often begins with antihistamines, which offers relief for the majority of kids and is a great starting point. There are other types of medications as well, such as nasal steroid sprays, that also may provide symptom relief.
Consideration of allergy testing (or any medical tests, for that matter) should involve discussion of how the test result will alter the diagnosis and/or management. In the case of allergies, testing can help confirm or deny the presence of allergies as the cause of symptoms, which will then alter the medications and avoidance strategies that are recommended. If your children are anything like mine, they will experience stuffy or runny noses throughout the year, but not all of them have allergies. If symptoms are persistent or progressing despite first line treatment with medications, then it would be very helpful to figure out exactly why those symptoms are present and the best course of treatment.
Hopefully this information helps you better understand why simply saying “It must be allergies” doesn’t always cut it. If your child is not getting the relief you expect or if questions remain, then consider an evaluation with a Board Certified allergist. Good luck with the runny noses, coughs, and rashes!