Histamines are chemicals that play a crucial role in the body's immune response. They are released by mast cells, a type of white blood cell, and basophils during an immune reaction. Histamines are involved in several physiological processes, including the regulation of stomach acid, dilation of blood vessels, and stimulation of sensory nerves.

When the body detects a potential threat, such as an allergen or injury, it releases histamines as part of the inflammatory response. Histamines increase the permeability of blood vessels, allowing immune cells to reach the affected area more easily. They also cause the characteristic symptoms of inflammation, such as redness, swelling, itching, and increased mucus production.

While histamines are essential for the body's defense against infections and injuries, an overactive or inappropriate immune response can lead to conditions like allergies, where the immune system reacts to harmless substances as if they were dangerous. This can result in symptoms such as sneezing, itching, hives, and nasal congestion.

Antihistamines are medications that work by blocking the effects of histamines. They do this by binding to histamine receptors, preventing histamines from attaching to these receptors and exerting their effects. By blocking histamine activity, antihistamines can help alleviate the symptoms of allergic reactions and inflammatory responses. Common symptoms that antihistamines can relieve include itching, sneezing, runny nose, and watery eyes.

There are two main types of histamine receptors: H1 receptors and H2 receptors. Antihistamines are often classified based on their selectivity for these receptors. H1 antihistamines are more commonly used to treat allergy symptoms, while H2 antihistamines are primarily used to reduce stomach acid production.

It's important to note that while antihistamines can be effective in managing allergy symptoms, they may have side effects, such as drowsiness, dry mouth, and blurred vision. It's recommended to use them under the guidance of a healthcare professional, especially if you have underlying health conditions or are taking other medications.