In this Article

• Introduction
• What's the difference between a controller and a reliever?
• What are antihistamines?
• How do antihistamines work?
• What are first generation antihistamines (OTCs)?
• What are second generation antihistamines (prescription)?
• What are common side effects of antihistamines?
• What are decongestants?
• How do decongestants work?
• When should I use topical decongestants?
• What are side effects of decongestants?
• What about combination antihistamine/decongestant preparations?
• Nasal Steroid Sprays
• Other nasal sprays that might help
• Tips for proper use of nasal sprays
• Nasal Allergy Medications At A Glance
• Nasal Allergy Medications Glossary
• Nasal Allergy Medications Index
• Find a local Asthma & Allergy Specialist in your town

What are antihistamines?

Antihistamines are one of the most commonly used OTC and prescribed medications. They are beneficial for nasal and eye allergies, eczema, and hives but tend not to be effective in asthma.

Antihistamine is a combination of two words. "Anti-" means against, and "histamine" is a naturally occurring chemical that is released by the mast cells.

How do antihistamines work?

Human cells have three different types of histamine receptors (H1, H2, and H3). Histamine works by attaching itself to these receptors on the surface of cells and thereby causing its effects. It is mainly through the H1 receptors that histamine causes symptoms of allergy. Antihistamines act by attaching to these same H1 receptor sites, thereby preventing histamine from binding to them. This action prevents the histamine from causing allergic symptoms.

Histamines can cause swelling, sneezing, itching (nose, throat, roof of mouth), and a runny nose through the nostrils or down the back of the throat (post-nasal drip). Antihistamines are effective in treating the sneezing, running, and itching. They usually begin working between 30 to 60 minutes after being taken. However, histamine is only one of the many chemicals involved in the allergic reaction, which explains why relief from antihistamines is usually only partial.

Allergy Fact

Bovet and Straub at the Pasteur Institute discovered the first antihistamine in 1937. It was too weak, however, and caused many side effects. In 1942, phenobenzamin (Antegan) was the first antihistamine used to treat allergies. Within a few years, diphenhydramine (Benadryl) and tripelennamine (PBZ) were formulated.