Allergic symptoms occur when your body wrongly recognises a food or something (such as pollen spores) in your environment as a threat and sends repair chemicals to deal with these perceived intruders. One of these repair chemicals, histamine, is released from repair cells called mast cells, which are scattered throughout the body.
This histamine can then bind with receptors to trigger increased blood flow to the surrounding area, which can lead to symptoms such as swelling and increased secretions, resulting in a blocked or a runny nose, watery eyes and, most importantly, itchiness.
Antihistamines don’t stop allergic reactions from happening, but they do block the histamine receptors from being able to be triggered by the histamine that is released, reducing your symptoms.
Antihistamines come in different forms, including tablets, nasal sprays, eye drops and syrups. There are many brands available on prescription from your GP or over the counter at your local pharmacy. Different antihistamines are better at treating different symptoms, so ask your GP or pharmacist to advise you on which antihistamine is best for your needs. Generally antihistamines are classified into 2 main groups:
Examples available in New Zealand include:
promethazine (Phenergan®, Allersoothe®)
Usually antihistamine tablets start to work within 30 minutes after being taken, and tend to be most effective within 1-2 hours after being taken.
Most people who take antihistamines do not have any serious side-effects. If side-effects do occur, they are usually minor.
Talk to your doctor before you begin taking antihistamines, as they could interact with your other medications or might not be suitable if you have other health conditions. Remember that cough or cold remedies often contain antihistamines, so if you are taking these as well you need to work out your total dosage to make sure you don’t take more than the total recommended amount for any one period.
Some people use antihistamines such as Phenergan and Vallergan as sedatives for their children, for example when they are travelling on a plane, but this can backfire as some children respond by becoming significantly more active (not a nice thing at 30,000 feet). Always check with your GP before giving your children medications.