Allergies and allergic reactions are common. About 1 in 3 Australians have allergies at some point in their lives. Usually, the symptoms of allergic reactions can be easily and effectively treated using a group of medicines called antihistamines.
If you think someone is having a serious allergic reaction, or anaphylaxis, call triple zero (000). Do not use antihistamines as they will work too slowly. Anaphylaxis should be treated with a shot of adrenaline into a muscle.
Allergies and histamine
Your body can become sensitive to things around you, like foods, plants, animals and medicines. If you are allergic to something, it is called an allergen.
When the body is exposed to allergens it releases histamine, a chemical. Histamine makes you sneeze, makes your nose run, and makes your eyes and skin itch, become red and swell up. In a way, it is trying to get you to sneeze out or scratch away the allergen.
Treating allergies and allergic reactions with antihistamines
Antihistamines are medicines that act by blocking the body's response to histamine. This reduces the severity of the reaction and eases the symptoms of allergy. Antihistamines are commonly used in the treatment of a number of conditions related to allergies and hypersensitivities like:
- hay fever (allergic rhinitis)
- hives (urticaria)
- allergic conjunctivitis
- eczema (dermatitis)
- reactions to bites and stings
Oral antihistamines can be used to treat all of the symptoms of an allergic reaction. Others come as eye drops or nasal sprays, for treating specific symptoms only. Some oral antihistamines may have a sedative effect, but others are non-sedating or non-drowsy.
Side effects of antihistamines
Some people get side effects from oral antihistamines like:
- dry mouth
- upset stomach
They usually don't last long.
If you use antihistamines you should be careful when operating machinery, such as driving a car. Even non-sedating antihistamines can make some people drowsy.
You should talk to a pharmacist or doctor before taking an antihistamine if you:
- have kidney or liver disease
- are a woman who is pregnant or breastfeeding
- are a man with prostate enlargement
People with porphyria should talk to their doctor or pharmacist before taking antihistamines.
If you have any questions or concerns about antihistamines, please talk to your doctor or pharmacist.
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Last reviewed: August 2019