Antihistamine vs. Histamine

What's the Difference?

Antihistamines and histamines are two substances that play opposite roles in the body's immune response. Histamine is a chemical released by mast cells during an allergic reaction, causing symptoms such as itching, sneezing, and inflammation. It acts by binding to specific receptors, triggering an inflammatory response. On the other hand, antihistamines are medications that block the effects of histamine by binding to the same receptors, preventing histamine from causing allergic symptoms. They are commonly used to relieve allergy symptoms like runny nose, watery eyes, and itching. While histamine is a natural compound produced by the body, antihistamines are synthetic drugs designed to counteract its effects.


DefinitionMedication that blocks the action of histamine receptorsA chemical compound released by cells in response to an allergic reaction
FunctionRelieves symptoms of allergies, such as itching, sneezing, and runny noseActs as a neurotransmitter and regulates various physiological processes
Role in Allergic ReactionsReduces the effects of histamine, which is responsible for allergic symptomsTriggers allergic symptoms by binding to histamine receptors
TypesFirst-generation and second-generation antihistaminesN/A (refers to the compound itself)
Common ExamplesDiphenhydramine, Loratadine, CetirizineN/A (refers to the compound itself)
Side EffectsDrowsiness, dry mouth, dizzinessN/A (refers to the compound itself)

Further Detail


Antihistamines and histamines are two important substances that play a significant role in our body's immune response and allergic reactions. While they are closely related, they have distinct attributes and functions. In this article, we will explore the characteristics of both antihistamines and histamines, highlighting their differences and similarities.

What is Histamine?

Histamine is a naturally occurring compound found in our body. It is released by mast cells and basophils, which are types of white blood cells, as part of the immune response. Histamine acts as a signaling molecule, binding to specific receptors in various tissues and organs. When histamine is released, it triggers a cascade of reactions that lead to inflammation, dilation of blood vessels, increased mucus production, and itching.

One of the primary functions of histamine is to defend the body against foreign substances. It plays a crucial role in allergic reactions, as it is responsible for the symptoms we experience, such as sneezing, itching, and watery eyes. Histamine also contributes to the regulation of stomach acid secretion and neurotransmission in the brain.

What are Antihistamines?

Antihistamines, as the name suggests, are drugs that counteract the effects of histamine. They work by blocking the histamine receptors, preventing histamine from binding and exerting its effects. Antihistamines are commonly used to relieve allergy symptoms, such as hay fever, hives, and itching.

There are two main types of antihistamines: first-generation and second-generation. First-generation antihistamines, such as diphenhydramine and chlorpheniramine, have been available for a long time and are known to cause drowsiness as a side effect. On the other hand, second-generation antihistamines, including cetirizine and loratadine, are less likely to cause drowsiness and are often preferred for daytime use.

Mode of Action

When histamine is released during an allergic reaction, it binds to specific receptors, namely H1, H2, H3, and H4 receptors. Antihistamines primarily target the H1 receptors, blocking the binding of histamine and preventing its effects. By doing so, antihistamines reduce the symptoms associated with allergies, such as itching, sneezing, and runny nose.

It is important to note that antihistamines do not completely inhibit the release of histamine or its actions on other receptors. They only compete with histamine for binding to the H1 receptors, reducing the overall histamine response in the body.

Side Effects

While antihistamines are generally safe and well-tolerated, they can cause certain side effects. The most common side effect of first-generation antihistamines is drowsiness, which can impair cognitive function and reaction times. This sedating effect is due to their ability to cross the blood-brain barrier and affect the central nervous system. Second-generation antihistamines, on the other hand, have a reduced sedative effect, making them more suitable for daytime use.

Other potential side effects of antihistamines include dry mouth, blurred vision, dizziness, and gastrointestinal disturbances. These side effects are usually mild and transient, but it is important to consult a healthcare professional if they persist or worsen.


Antihistamines are primarily used to relieve allergy symptoms, such as hay fever, allergic rhinitis, and urticaria (hives). They can effectively reduce itching, sneezing, nasal congestion, and watery eyes associated with these conditions. Antihistamines are also used in the management of motion sickness, as they can help alleviate nausea and vomiting.

Additionally, antihistamines may be prescribed to manage certain skin conditions, such as eczema and atopic dermatitis, as they can help reduce itching and inflammation. Some antihistamines also have sedative properties, which can be beneficial for individuals experiencing difficulty falling asleep.


In summary, histamine is a naturally occurring compound released by the body during allergic reactions and immune responses. It triggers various symptoms, including itching, sneezing, and inflammation. Antihistamines, on the other hand, are drugs that block the effects of histamine by binding to its receptors. They are commonly used to relieve allergy symptoms and can be categorized as first-generation or second-generation based on their sedative effects.

While antihistamines effectively alleviate allergy symptoms, they may cause side effects such as drowsiness, dry mouth, and blurred vision. It is important to choose the appropriate antihistamine based on individual needs and consult a healthcare professional if any concerns arise. Understanding the attributes of both antihistamines and histamines can help individuals make informed decisions regarding their use and management of allergic conditions.

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