Allergies and Causes

BY SECOND CONSULT Published on July 19, 2021

Exposure to airborne allergies can trigger allergic rhinitis (hay fever) and asthma, which can result from both genetic and environmental factors. Allergens such as pollens, pet dander, house dust mites, molds, cockroaches, and rodents are some of the sources of allergens.


Plants release pollen grains during the spring, summer, and fall seasons to fertilize other plants of the same species. Pollen allergies affect people during the period when the airborne pollen grains they are allergic to are in the air, resulting in symptoms of allergic rhinitis or asthma.

However, seasonal symptoms are not always caused by pollen. The rhinovirus, responsible for causing the common cold, triggers runny noses and asthma attacks during the fall and spring seasons. Trees, weeds, and grasses are the primary sources of allergenic pollens, and these plants produce small, dry, and light pollen grains that are dispersed by the wind.


Molds can be found both indoors and outdoors, and wind carries outdoor molds similarly to pollens. Some molds can cause health issues, while others do not. Alternaria, a mold found outside, has been associated with severe asthma, while Aspergillus, another type of mold, is linked to a chronic and severe form of asthma.

Indoor molds can also cause allergies and other health problems. Living in a damp or moldy environment can make some people feel unwell, even if they do not have allergies. However, there has been little research examining the health effects of indoor molds.

Other Indoor Allergens

Exposure to house dust during household chores such as vacuuming or sweeping can trigger allergic rhinitis and asthma. House dust is a mixture of substances, and it may contain allergens from house dust mites, pets, mold, cockroaches, and rodents.

Sensitive individuals can experience symptoms of allergic rhinitis and asthma when exposed to animals such as cats and dogs. However, early-life exposure to these animals may provide a protective effect.

Environmental Allergies: Symptoms

Symptoms of allergic rhinitis and asthma include the following:

  • Runny nose and mucus production
  • Sneezing
  • Itchy nose, eyes, ears, and mouth
  • Stuffy nose
  • Red and watery eyes
  • Swelling around the eyes
  • Coughing
  • Wheezing
  • Chest tightness
  • Shortness of breath

Environmental Allergies: Diagnosis

A healthcare professional may perform skin, blood, or allergy component tests to help diagnose environmental allergies.

Skin Tests

A healthcare professional can use a skin prick test to determine if a specific allergen triggers a person's sensitivity. When a person's immune system produces antibodies, known as IgE, against an allergen, they become "sensitive." IgE attaches to mast cells that are present in the nose and airways as well as the skin.

During a skin prick test, a healthcare professional pricks the skin on the arm or back using a piece of plastic and then introduces a small amount of allergen extract just below the skin's surface. If a person is sensitive to the allergen, the allergen binds to IgE on the mast cells in the skin, leading to the release of histamine and other chemicals that cause redness, itching, and minor swelling.

Healthcare professionals often attempt to correlate the skin test results with the type of allergen exposures that a person may have had.

Blood Tests

Doctors may measure levels of allergen-specific IgE antibodies in a blood sample instead of performing a skin test. Both skin and blood tests can detect IgE antibodies in most people who are sensitive to a particular allergen. However, a positive blood test to an allergen does not necessarily indicate that the person's symptoms are caused by that allergen.

Allergy Component Tests

Allergens consist of various components, and some components are more likely to cause symptoms than others. Blood tests, known as allergy component tests, can identify the specific component of an allergen that the IgE in a person's blood recognizes. This information can help healthcare professionals determine if the allergen is likely to cause symptoms. It is important to note that a positive skin or blood test does not always indicate that a person's symptoms are caused by a particular allergen.

Environmental Allergies: Treatments

Medications are available to control symptoms of allergic rhinitis and asthma. Health professionals may prescribe immunotherapy as a long-term treatment to modify the body's immune response to allergens and change the course of allergic disease for people with environmental allergies.

Medications to Treat Allergic Rhinitis

Certain over-the-counter and prescription medications may help reduce the severity of allergic rhinitis symptoms.


Antihistamines, which are taken by mouth or as a nasal spray, can relieve sneezing and itching in the nose and eyes. They reduce runny nose and, to a lesser extent, nasal stuffiness.

Nasal Corticosteroids

Anti-inflammatory medicines called nasal corticosteroid sprays help to block allergic reactions and are widely considered the most effective medication for allergic rhinitis. They can reduce all symptoms, including nasal congestion, and have few side effects compared to corticosteroids taken by mouth or injection. Combining a nasal antihistamine with a nasal corticosteroid seems to be more effective than using either of the sprays alone. However, it is not clear whether taking an oral antihistamine with a nasal corticosteroid is helpful.


Oral and nasal decongestants help shrink the lining of the nasal passages, relieving nasal stuffiness. Decongestant nose drops and sprays are intended for short-term use. When used for more than a few days, these medicines may lead to even more congestion and swelling inside the nose. Doctors may recommend using decongestants along with an antihistamine because antihistamines do not have a strong decongestant effect.

Leukotriene Receptor Antagonists

Leukotriene receptor antagonists, such as the prescription drug montelukast, block the action of leukotrienes, chemical messengers involved in allergic reactions.

Cromolyn Sodium

Cromolyn sodium is a nasal spray that blocks the release of chemicals that cause allergy symptoms. The drug causes few side effects, but must be taken four times a day.

Medications to Treat Asthma

Asthma medications are divided into two categories: relievers and controllers. Relievers are used for asthma attacks and not for long-term treatment of the disease. Controllers are used to prevent asthma symptoms. For controllers to work properly, people with asthma have to use them consistently, even when feeling well.


Short-Acting Beta-Adrenergic Agonists

Albuterol is a short-acting beta-agonist (SABA) that can relieve symptoms of asthma immediately and lasts for four to six hours. It does not decrease allergic inflammation, but rather relaxes the muscles around the airway that tighten when an allergic person is exposed to an allergen or other asthma trigger. People with occasional asthma attacks may use SABAs as the only medication as needed. Those who take controller medications often use SABAs for symptom relief.

Oral Corticosteroids

Doctors typically use oral corticosteroids like prednisone, methyl prednisolone, and dexamethasone to treat severe asthma attacks. People with very severe asthma may take corticosteroids as controller medications, using them daily or every other day. Long-term use of oral corticosteroids at high doses can cause several side effects, including weight gain, high blood pressure, diabetes, brittle bones, thinning skin, muscle weakness, and cataracts. Doctors treating people with severe asthma may use various medication combinations to try to reduce the dose of corticosteroids.


Inhaled Corticosteroids

People with persistent asthma can benefit from inhaled corticosteroids, which effectively improve quality of life and prevent severe asthma attacks. Inhaled corticosteroids can sometimes lead to mouth yeast infections. Long-term use of high doses may also cause some of the side effects common with oral corticosteroids, such as brittle bones and a higher risk of cataracts. For moderate to severe asthma, doctors may prescribe inhaled corticosteroids in combination with long-acting beta-adrenergic agonists.

Leukotriene Receptor Antagonists and 5-Lipoxygenase Inhibitors

Leukotriene receptor antagonists (LTRAs) block the action of leukotrienes, chemical messengers involved in allergic reactions. They may be used alone to treat mild asthma or along with an inhaled corticosteroid to treat moderate asthma, as well as to treat allergic rhinitis. People who have both mild asthma and allergic rhinitis can take an LTRA to treat both conditions.

A related medication, called zileuton, prevents leukotriene production by blocking an enzyme called 5-lipoxygenase. Zileuton is only used for severe asthma, and evidence suggests that it may be particularly useful for people with asthma who have reactions to aspirin, a syndrome called aspirin-exacerbated respiratory disease, or AERD.

Long-Acting Beta-Adrenergic Agonists

In combination with an inhaled corticosteroid, long-acting beta-agonists (LABAs) are effective for asthma control. LABAs, the effects of which last for 12 hours, typically are not used alone because some studies have suggested that LABAs can be harmful if used without an inhaled corticosteroid.

Cromolyn Sodium

Doctors may recommend cromolyn sodium to treat mild asthma in young children. Liquid cromolyn sodium is placed in a mist-generating machine called a nebulizer, and children breathe in the mist.


The Food and Drug Administration has approved the injectable medication omalizumab to treat allergic asthma. Omalizumab works by binding to IgE, the antibody responsible for allergies, and removing it from the body. Omalizumab can prevent severe episodes of asthma in people whose asthma is not adequately controlled by other medications.

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