When you have an allergic reaction, the immune system will release a chemical called histamine that triggers symptoms like nasal congestion, runny nose, itchy eyes, and rash. The release of histamine can also spur a reaction in the lungs, leading to an asthma attack.
This article explains how allergies and asthma are related and ways to block the effects of histamine so that you can better avoid an allergic asthma attack.
What Are Allergies?
An allergy is an overreaction of the immune system to an otherwise harmless substance known as an allergen.
Under normal circumstances, the immune system will respond to a threat, like a virus or an injury, by releasing histamine and other chemicals that cause inflammation. The aim of inflammation is to dilate (widen) blood vessels so that larger immune cells can access and neutralize the threat.
However, with allergies, the immune response is inappropriate. When this happens, the sudden dilation of blood vessels causes fluids to leak into surrounding tissues and mucus membranes, leading to rash, nasal congestion, runny nose, and watery eyes.
At the same time, histamine overexcites nerves in the skin and mucus membranes, causing itchiness and sneezing.
What Is Asthma?
Asthma is an inflammatory lung disease that causes acute (sudden and severe) episodes of wheezing, shortness of breath, chest tightness, and coughing. Sputum, a thick mixture of mucus and saliva, may also be secreted by the lungs and be difficult to cough up.
With asthma, the immune symptom will respond to any number of triggers by causing acute inflammation of the airways, most especially the larger passages called the bronchi and bronchioles. The inflammation, in turn, causes airway passages to constrict (narrow) and spasm, leading to an asthma attack.
Asthma is thought to be caused by a combination of genetics and environmental factors. Environmental factors include exposure to air pollution and allergens.
When an allergen triggers asthma symptoms, it is referred to as either allergy-induced asthma or allergic asthma.
How Histamine Works
Histamine is a nitrogen-based compound involved in many different body functions, including vasodilation (the widening of blood vessels), nerve stimulation, the sleep-wake cycle, and the secretion of stomach acids and respiratory mucus.
During an allergic reaction, the immune system will release proteins called antibodies that set off a chain reaction of events. The antibody associated with allergies, called immunoglobulin E (IgE), causes white blood cells—known as basophils and mast cells—to degranulate (break open) and spill histamine and other inflammatory chemicals into the body.
The released histamine then binds to receptors on cells of the skin and mucus membranes that effectively “switch on” the inflammatory response.
Reaction Symptoms
With allergic asthma, the degranulation of mast cells in the airways is the primary cause of an asthma attack. As histamine is released, it immediately spurs airway hyperresponsiveness in which the bronchi and bronchioles become overly sensitive to environmental stimuli (such as cold, smoke, or dust).
The allergic reaction will also cause a type of white blood cell known as an eosinophil to degranulate and release inflammatory compounds called cytokines and leukotrienes into the airways, causing:
Bronchoconstriction: This is the sudden narrowing of airways, making it harder to breathe. Leukotrienes are the main cause of this effect. Bronchospasms: These are spontaneous convulsions of muscles lining the airways, causing coughing and chest pain. Excess mucus production: The sudden narrowing of airways also causes the excess secretion of mucus, further blocking airways and causing high-pitched whistling sounds known as wheezing.
Eosinophils are primarily found in tissues. The severity of an asthma attack generally corresponds to the concentration of eosinophils in the airways.
Treatment
The primary goal of treating any asthma attack is to reverse the symptoms of bronchoconstriction and bronchospasm. This typically involves rescue inhalers containing the drug albuterol which widens the airways and eases spasms. Mucolytic drugs can also help clear excess mucus from the lungs.
Antihistamines commonly used to treat allergies, cannot stop an asthma attack but can block the effects of histamine and may help ease the severity of an attack. Options include:
Allegra (fexofenadine) Benadryl (diphenhydramine) Claritin (loratadine) Zyrtec (cetirizine)
Antihistamines may also help prevent an attack, particularly when taken prophylactically (as daily preventive therapy) during allergy season when the risk of an attack is high.
Leukotriene-modifying drugs like Singulair (montelukast) may also help control or prevent symptoms of asthma triggered by allergies. It is also prescribed prophylactically for people at risk of severe allergic asthma attacks.
When to See a Healthcare Provider
According to the American Lung Association, it is important to call your healthcare provider immediately if your rescue inhaler fails to provide relief. This includes wheezing and coughing that persists or worsens, feeling dizzy or faint, or having trouble doing routine activities like cooking or cleaning.
On the other hand, you need to call 911 or seek emergency care if you experience any of the following severe symptoms of asthma:
Nostrils that flare as you breathe in Bluish discolorations of lips or skin (cyanosis) The sucking in of the skin between the ribs as you inhale (intercostal retractions) Rapid breathing, generally 30 or more breaths per minute (tachypnea) Difficulty talking while walking
Summary
Allergy-induced asthma, also known as allergic asthma, is caused by the release of histamine during an allergic reaction. When this happens, the airways of the lungs become overly sensitive to environmental triggers, causing them to narrow, spasm, and become congested with mucus.
Allergic asthma attacks are treated with rescue inhalers containing albuterol. Antihistamines and leukotriene-modifying drugs like Singulair (montelukast) may be prescribed to help control or prevent allergic asthma attacks.
A Word From Verywell
If you have asthma and find it harder to control your symptoms during allergy season or when around pets, allergic asthma may be the cause.
If you suspect you have allergic asthma, allergy tests can be performed by a specialist known as an allergist. Blood tests can confirm the presence of IgE antibodies, while skin prick tests can pinpoint which specific allergens you are sensitive to so that you can avoid them.
Shortness of breathWheezingCoughingRapid breathingChest pressureRapid heart rate
An outbreak of rash or hivesShortness of breathWheezingNausea or vomitingSudden, severe diarrheaLightheadedness, dizziness, or faintingRapid or irregular heartbeatsSwelling of the face, tongue, or throatA feeling of impending doom
