What are antihistamines?

Antihistamines are medicines you can take to treat allergies and allergic reactions like insect bites and stings.

About 1 in 5 Australians will have allergies at some time in their lives.

How do antihistamines work?

Antihistamines help prevent or treat your allergy symptoms by blocking a substance called histamine.

Allergies happen when your immune system confuses a harmless substance for something dangerous, such as pet hair. Your body reacts by releasing a substance called histamine.

Histamine makes your blood vessels bigger and causes your skin to swell. This can cause allergy symptoms like:

• sneezing
• a runny nose
• watery and itchy eyes
• a rash

What are antihistamines used for?

You can take antihistamines to help with your symptoms if you have:

• hay fever — also called allergic rhinitis
• an allergy to house dust mite, mould or pet hair
• allergic conjunctivitis
• hives — also called urticaria
• allergic reactions to insect bites or stings
• food allergies

Sedating antihistamines are sometimes used for:

• itch
• rhinitis
• nausea and vomiting

What forms of antihistamines are available?

Antihistamines are available in different forms, such as:

• tablets
• liquids
• nasal (nose) sprays
• eye drops

The best one for you will depend on which symptoms trouble you the most.

Ask your pharmacist or doctor what treatment is right for you.

There are 2 main types of antihistamines:

Less or non-sedating antihistamines — these usually do not make you sleepy. They include:

• desloratadine
• fexofenadine
• loratadine
• bilastine
• cetirizine — of the less sedating antihistamines, cetirizine is the most likely to cause sleepiness

Sedating antihistamines — these can make you feel sleepy. They include:

• dexchlorpheniramine
• diphenhydramine
• doxylamine
• promethazine

Sedating antihistamines aren'trecommended for treating allergic reactions.

In Australia, most antihistamines are available from pharmacies and supermarket without a prescription.

Ask your pharmacist for advice if you think you might need to take an antihistamine. They can help you chose an antihistamine to suit your needs.

Tell your pharmacist if you are pregnant or if you are taking other medicines. They will check if it is safe for you to take an antihistamine.

What are the possible side effects or risks of antihistamines?

Like all medicines, antihistamines can cause side effects.

Side effects of non-sedating antihistamines include:

• headache
• fatigue (tiredness)
• insomnia
• rash

Side effects of sedating antihistamines include:

• drowsiness
• problems with co-ordination
• dry mouth
• blurred vision

If you've taken antihistamines, you should be careful when operating machinery, including driving a car. Even non-sedating antihistamines can make some people sleepy.

Studies have shown that taking sedating antihistamines might increase the chance of getting dementia, especially in people older than 65 years.

Do not use sedating antihistamines in children who are under 6 years for the treatment of:

• cough
• cold symptoms
• flu symptoms

Do not give sedating antihistamines to children under 2 years for any reason.

Talk to your doctor or pharmacist about the risks before taking sedating antihistamines.

When should I see my doctor?

You should talk to a pharmacist or doctor before taking an antihistamine if you:

• have kidney or liver disease
• are pregnant or breastfeeding
• have prostate problems

If you think you may have a food allergy or sensitivity, talk to your doctor. Do this before taking an antihistamine or cutting a certain food from your diet.

Are there alternatives to antihistamines?

There are other options, but these depend on what you are being treated for. For example, you could use a cream for skin rash.

Your pharmacist can also help you find alternative treatment for your symptoms.

Resources and support

For more information and support, try these resources.

• Australasian Society of Clinical Immunology and Allergy information for patients and carers.
• Download the AirRater app to track your hay fever symptoms and monitor allergens in the environment.
• Check the pollen count in your area at Pollen Forecast.
• Asthma Australia explains how hay fever can make asthma worse.
• Allergy and Anaphylaxis Australia has information on urticaria (hives) and angioedema.

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with you 24 hours a day, 7 days a week.