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Allergies are the result of an over-reactive immune system.1 When allergies occur, the immune system mistakenly identifies an allergen (pollen, pet dander, mold, and dust mites) as an “invader.”3 In response, the body mounts an inappropriate immune response—similar to one that it would launch against something much more harmful, such as the cold virus.5

To rid itself of the “invader,” the immune response triggers a response that results in you experiencing symptoms—such as sneezing, runny nose, and itchy, watery eyes.2

The diagram below takes you through the stages of a typical allergy attack, starting from the allergens entering your nose, to showing how your immune system responds, and the resulting symptoms.


Today, 50 million Americans suffer from nasal allergies.9 Studies say that climate change may be to blame. With plants producing more pollen per year, sending more allergens into the air we breathe, our immune systems are working overtime.10,11


When allergens like mold and pollen enter the body, specialized detecting cells identify them and then rush to the lymph nodes.3,4


Signaling cells examine the potential allergic situation and if they detect a threat to the body, they call upon helper cells5 to combat it. 


Helper cells instruct antibody producing cells to start producing antibodies that bind to the mold or pollen fragments.6


When the antibodies are released, responder cells take action. They release inflammatory substances* that trigger an allergic response.7

*Six key substances— histamine, cytokines, leukotrienes, prostaglandins, tryptases and chemokines—are involved in the allergic immune response.


For someone with allergies, this is when symptoms may appear, such as itchy, watery eyes, runny nose, sneezing
and congestion.8


1. Wallace DV, Dykewicz MS, Bernstein DI, Blessing-Moore J, Cox L, Khan DA, et al. The diagnosis and management of rhinitis: an updated practice parameter. J Allergy Clin Immunol. 2008 Aug:122(2). [PubMed]

2. Bousquet J, Schünemann HJ, Samolinski B, et al. Allergic Rhinitis and its Impact on Asthma (ARIA): achievements in 10 years and future needs. J Allergy Clin Immunol. 2012;130(5):1049-62.

3. Glossary of HIV/AIDS-Related Terms. AIDSinfo website. Terms_English.pdf Published 2011. Accessed March 2014.

4. Angel C, Chen C, Horlacher O, et al. Distinctive localization of antigen-presenting cells in human lymph nodes. Blood. 2009; 113 (6): 1257-1267.

5. Bell, E. T-cell-APC interactions. Nat Rev Immunol. 2004; 4 (12): 930.

6. Alberts B, Johnson A, Lewis J, et al. Helper T Cells and Lymphocyte Activation. In: Molecular Biology of the Cell. 4th ed. New York, NY: Garland Science; 2002.

7. Stone KD, Prussin C, Metcalfe DD. IgE, mast cells, basophils, and eosinophils. J Allergy Clin Immunol. 2010; 125 (2): 73-80.  

8. Allergic Reactions. MedlinePlus website. Published 2012. Accessed March 2014.          

9. Allergy Facts. ACAAI website. Accessed August 2015.

10. National Wildlife Federation Extreme allergies and global warming. Accessed April 25.2014

11. Root TL Price JT Hall KR. Schneider SH Rosenzweig C. Pounds JA Fingerprints of global warming on wild animals and plants Nauture. 2003 421(6918):57-60