Antihistamines are used to treat a variety of allergies.

They do not cure them but can be used to prevent a reaction from happening or to treat symptoms during a flare-up.

Often allergy symptoms can be mild and pass quickly, thereby not requiring treatment. However, severe symptoms can hinder a person’s quality of life and medicine may be advised.

Those struggling to cope with allergy symptoms should contact their doctor about treatment options. Antihistamines can offer effective treatment for seasonal allergies such as hay fever, as well as allergies to pet fur, house dust mites and insect bites.

This type of medication is available in a variety of strengths which means that some varieties are available to buy over-the-counter; whereas others require a prescription from a doctor.

What happens during an allergic reaction?

Histamine is a chemical naturally made by the body to perform a variety of functions.

It is produced in mast cells that form part of the body’s immune system. These cells are housed within the zones of the body that come into contact with environmental substances most often; the respiratory tract and the skin.

The immune system continually analyses these areas for any problems such as broken skin or foreign substances.

When an incident is detected, histamine is released from the mast cells in order to bind with another type of cell known as H1 receptors.

Under normal circumstances this reaction is helpful as it allows for the quick distribution of chemicals and cells to heal the area or fight off the offending substance.

However, the immune system of someone with an allergy will also treat harmless substances such as pollen and pet dander as a threat. This hypersensitive reaction becomes a hindrance as areas of the body become swollen, red or itchy.

Antihistamines counteract the reaction by blocking H1 receptors, so any histamine that is released is not able to reach its target area. The histamine cannot bind with the H1 receptors and so symptoms should be reduced or prevented from occurring. 

Sometimes antihistamines are used to treat nausea and vomiting symptoms, particularly in travel cases or morning sickness. It is not yet fully understood how some antihistamines help to reduce these symptoms, but it is thought that they block H1 receptors in the area of the brain which controls the urge to vomit.

What types of antihistamines are available?

Antihistamines are often split into two groups: first generation and second generation.

The first generation group is the older version of the medication and can cause side effects such as drowsiness.

With developments in medicine in recent years new antihistamines have been released that do not cause this side effect. These are known as second and third generation antihistamines.

How are antihistamines taken?

Antihistamines are available in a variety of forms including eye drops, nasal sprays, tablets, capsules, creams and lotions.

Each different version might be better suited at treating certain symptoms more than others. Your doctor or your pharmacist will be able to help you choose the best option.

Antihistamines are often most effective when used as a preventative measure, so that the immune system doesn’t get a chance to react. However, they can be used to relieve symptoms as well, when a reaction is in progress.

Page last reviewed:  01/10/2020