Many people who experience seasonal or chronic allergies report a noticeable increase in heart rate, often referred to as palpitations. The body’s reaction to an allergen directly influences cardiovascular function. Allergies represent an immune system overreaction to a typically harmless substance, such as pollen. This defensive process releases powerful chemical messengers that affect the body, including changing heart rhythm and speed. The elevated heart rate can result from the body’s internal immune response or be a side effect of common allergy treatments.
The Body’s Direct Response to Allergens
The immune system’s encounter with an allergen triggers specialized cells, particularly mast cells, to release inflammatory mediators, the most recognized of which is histamine. Histamine acts rapidly on various tissues and is a primary cause of classic allergy symptoms like itching and sneezing. Its effects extend beyond the nasal passages and skin, significantly impacting the circulatory system.
A major action of histamine is to promote systemic vasodilation, the widening of blood vessels throughout the body. This widespread dilation reduces resistance within the vascular network, causing a noticeable drop in overall blood pressure. To maintain adequate perfusion, the heart must beat faster and pump harder to compensate for this reduced pressure. This compensatory increase in heart rate is known as reflex tachycardia.
Histamine can also act directly on the heart muscle itself. H2-receptors are present in the heart tissue. When histamine is released during a systemic allergic response, stimulating these receptors can lead to a direct increase in the heart’s rate and its force of contraction.
The physical and emotional stress associated with an allergic reaction also contributes to a faster heartbeat. Severe symptoms, such as difficulty breathing, activate the body’s sympathetic nervous system, or “fight-or-flight” response. This response releases catecholamines, including epinephrine (adrenaline), which stimulates the heart to beat faster and more powerfully.
Heart Rate Changes Caused by Medication
While the immune response can directly speed up the heart, many people experience a rapid heart rate as a side effect of common allergy medications. Decongestants, used to clear nasal congestion, are sympathomimetic agents structurally similar to adrenaline. These medications, which include pseudoephedrine and phenylephrine, stimulate alpha-adrenergic receptors in the blood vessels lining the nasal passages.
The intended effect is vasoconstriction, which reduces swelling and mucus production. However, because these medications circulate throughout the body, they can affect blood vessels and receptors beyond the nasal cavity. The systemic action of these decongestants can lead to unintended cardiovascular effects, including palpitations, increased blood pressure, and a faster heart rate.
Studies show that pseudoephedrine use can result in an elevation in heart rate, averaging around 2.83 beats per minute. While this effect is minor for most healthy individuals, it can be problematic for people with pre-existing heart conditions, such as high blood pressure. Healthcare providers advise those with cardiovascular disease to avoid or use caution with oral decongestants.
In cases of severe, life-threatening allergic reactions, the rescue medication administered is epinephrine. This drug is specifically designed to be a potent stimulant to counteract the dangerous effects of a severe reaction. Epinephrine rapidly increases heart rate and constricts blood vessels to raise critically low blood pressure and improve breathing. This demonstrates the powerful pharmacological effect of sympathetic stimulation on the heart.
Recognizing Signs of Severe Allergic Reactions
An elevated heart rate during an allergy episode is usually a harmless symptom, but it can also indicate a severe, life-threatening event known as anaphylaxis. Anaphylaxis involves the rapid onset of multiple symptoms affecting different body systems, requiring immediate medical attention.
In a severe reaction, a rapid heart rate often coincides with signs of circulatory shock, which occurs when the body’s blood pressure drops dangerously low. Look for a combination of symptoms that accompany the racing heartbeat, such as difficulty breathing, wheezing, or tightness in the chest. Other red flags include swelling of the throat, tongue, or face, along with feeling light-headed, dizzy, or fainting.
If a rapid heart rate occurs with any of these severe symptoms, it constitutes a medical emergency. Immediate action should be taken by calling emergency services and administering an epinephrine auto-injector if one is available and prescribed. Even if symptoms appear to improve after using an auto-injector, the person should still be taken to the emergency room for continued monitoring and care.