» Histamine
a substance which plays a major role in many allergic reactions. It dilates blood vessels and makes the vessel walls abnormally permeable.

» Hives
an allergic skin condition characterized by itching, burning, stinging and the formation of smooth patches, usually red. Technical name: Urticaria

» Hydrated
in combination with water.

» Hydrocortisone
a topical corticosteroid, of a class of drugs called steroids, used to reduce swelling and inflammation; side effects include thin skin, stretch marks and excess body hair, as well as damage to the immune system; not recommended for long-term use.

» Hyperirritability
easily irritated.

» Hypersensitivity
a pattern of immune reactivity that begins within minutes of exposure to an antigen, often presented as hives.

» Hypothyroidism
deficiency of thyroid hormone which is normally made by the thyroid gland which is located in the front of the neck.