It causes an increase in blood flow to the area of the allergy, and the release of other chemicals that add to the allergic response.
All this results in the symptoms of an allergic reaction.
Antihistamines can be used in children though age limits do apply: hydroxyzine is not recommended for children under six months, and promethazine and alimemazine are not recommended for children under two years.Sedating antihistamines will usually be prescribed to be taken at bedtime and are usually only used for short periods of time, for example when a severe flare-up is causing intense itching.All medicines have possible side-effects, though you may not necessarily experience any.Side-effects from antihistamines are more likely to occur in children and the elderly, and some of the most common ones associated with this type of medicine are listed below.In addition, if you have liver or kidney disease you may need a lower dose of these medicines, though this depends on the particular medicine prescribed.
Medicines that are not totally essential should ideally be avoided during pregnancy, and pregnant women should not take antihistamines unless prescribed by a doctor.
The most commonly used ones are promethazine (Phenergan), hydroxyzine (Atarax), or alimemazine (Vallergan).
Non-sedating antihistamines such as cetirizine or loratadine are not effective at controlling the itch of eczema.
More information about the potential side-effects associated with each specific medicine can be found in the patient information leaflet that will be provided with the medicine.
It is important to tell your doctor or pharmacist what medicines you are taking, including those bought without a prescription and herbal medicines, before you start taking a new medicine.
It can also cause more severe allergic reactions such as angioneurotic oedema, which involves severe swelling of the eyes, lips, tongue or throat.