How antihistamines help treat allergy symptoms
"Allergies can be triggered by any number of allergens, from pollen to dust mites, moulds or pet dander", says Cape Town allergologist Dr Candice Royal. If you’re allergic, your body sees them as foreign invaders and releases histamine and other chemicals into your bloodstream to fight them off.
Histamines: The basics
When there’s too much histamine circulating, unwanted “histaminergic” effects occur. A flood of immune cells into your nasal membranes causes these to swell and get congested, producing excessive mucous to wash out the allergens. That’s when you develop that runny or blocked nose, itchy and teary eyes, headache, irritability and poor concentration, among other unpleasant symptoms.
In severe cases, without intervention, breathing difficulties or low blood pressure and shock (anaphylaxis) can set in, which if not treated quickly and effectively, can be fatal.
How do antihistamines work?
You can’t always avoid allergen triggers, but your healthcare provider can advise prescription, or over the counter, medication to ease the symptoms. "Antihistamines compete with histamine receptor sites located throughout the body, and attempt to reduce the action of the histamine", says Bloemfontein paediatrician and allergist Dr Pieter de Waal.
"They are the most common drug prescribed in patients with allergic conditions and should be given early to any patient suffering from an anaphylactic event – not forgetting the potential life-saving effect of adrenaline in this situation as a priority."
What side effects can you expect when taking antihistamines?
All antihistamines counter the effects of histamine, but they can differ considerably in their chemical structure, duration of action, potential side effects and ability to interact with other drugs you may be taking. The good news is that antihistamines also come in a variety of forms, from tablets to syrups, nasal sprays, eye drops and intravenous formulations, with the newer, second-generation antihistamines also carrying fewer side-effects than the older, first-generation options.
"Second-generation antihistamines tend to be less sedative or not sedative at all", says De Waal, "sparing you the drowsiness that can affect your ability to work efficiently and drive or operate equipment safely". They are also longer-acting, so they can usually be taken once daily rather than three or four times.
Dry mouth and constipation, a problem with first-generation antihistamines, are less common, and hyperactivity, insomnia and convulsions, which can potentially occur with first-generation treatments, are less likely. You’re also less likely to have an increased appetite and serious side effects if taking them with other drugs, such as antibiotics.
"Most of the newer antihistamines don’t cause side effects," confirms Royal.
After taking your medical history, your health professional will advise you on which antihistamine is most suitable for you, depending on your age, underlying medical conditions and use of other medications, occupation, lifestyle and what you can afford.
Read the directions carefully – it’s important to use antihistamines exactly as prescribed. And, don’t use OTC allergy medication without talking to your health-care provider, especially if you are pregnant or have a chronic condition like high blood pressure or heart disease.
Also read: Is it an allergy or is it a virus?
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