This means it has an effect on small blood vessels, resulting in dilated capillaries (redness), and leakage of protein-rich fluid into surrounding skin (swelling).Histamine affects nearby nerves resulting in itching.Histamine is stored in Antihistamines are medications that counteract the effect of the natural chemical histamine.They are valuable drugs to reduce symptoms due to allergic diseases, especially those mediated by histamine.Topical antihistamine creams, present in many forms of over-the-counter anti-itch creams, should not be used for the treatment of hives or other skin allergies.
For example, antihistamines are commonly combined with decongestants (for example, Claritin-D, Zyrtec-D, Allegra-D), a class of medicine that is used to dry up the nasal passages and relieve head congestion.
As well as tablets, antihistamines are available as injections, elixirs, and creams.
An injection can be given in case of severe allergic reaction (although in such cases, adrenaline (epinephrine) may be more appropriate and can be life-saving).
Older antihistamines, such as diphenhydramine (Benadryl), chlorpheniramine (Chlor-Trimeton), and hydroxyzine (Atarax), also work well but have many side effects.
Oral antihistamines work well when taken as-needed, meaning that allergy symptoms improve within an hour or two of taking the medication.