Histamine is a chemical produced by an allergy-producing white blood cells called mast cells. Histamine causes allergic reactions in the skin – HIVES (urticaria) or SWELLING (angioedema) and nose and eyes – SNEEZING, RUNNY NOSE, ITCHY EYES (hay fever).

Antihistamines block the effect of histamine. They have been used to treat allergies since the 1940s.

The first generation antihistamines cause drowsiness.

  • alimemazine (Vallergan)
  • clemastine (Tavist)
  • diphenhydramine (Benadryl)
  • ketotifen (Zaditor)
  • promethazine (Phenergan)

Because of side-effects these antihistamines should be avoided. Piriton is still used in young children as it is one of the only antihistamines licenced in this age group.

Second generation antihistamines cause less drowsiness and work for up to a day.

  • cetirizine (Zyrtec)
  • desloratadine (Neoclarityn)
  • fexofenadine (Allegra)
  • levocetirizine (Xyzal)
  • loratadine (Claritin)

Second generation antihistamines are now recommended to treat allergies symptoms. They are similar in their effectiveness and one is recommended dependent on market price.

Antihistamines should not be used to treat the itch of eczema or wheeze of asthma, as other allergy chemicals cause these symptoms and these drugs do not work for these kind of allergies.