There are 4 main types of allergic reactions and the most common one that affects people is called Type I hypersensitivity. In this type of reaction allergic antibodies or IgE trigger a series of chemicals including histamine to be released into the skin, eyes, nasal passages, lungs and even the GI tract. This can cause itching, sneezing, runny nose, nasal congestion, cough, bronchospasm and in severe cases, even anaphylaxis. Allergic reactions are triggered most often by pollen, animal dander, mold, food, bee stings, and drugs.
While hives are often associated with allergic reactions, especially to foods, insects and drugs, there are other triggers that are not allergic in nature. Hives are a red, raised itchy rash that can occur anywhere on the body and typically come and go within minutes to hours. Individual hives do not usually last in the same exact location for more than a day but move around. Most often when a patient presents to the ER or Urgent care with an acute bout of hives, no allergic trigger is found. This is because hives can be caused by a current bacterial or viral infection or even an infection that happened weeks prior.
The main task for a doctor seeing someone with acute hives is to determine if there is a clear allergic trigger and to distinguish a bout of hives from a mild systemic allergic reaction. Often patients come to see me after an ER visit for hives and want to be allergy tested. This is where it gets tricky as there is no need for allergy testing if there was not a clear trigger like a drug, a new allergenic (ie.tree nuts or shellfish) or an insect sting that preceded the onset of the hives. In my experience, patients who’ve had an unexplained bout of hives just want answers and the hard truth is that doing a bunch of food or airborne allergy tests is not necessary and rarely provides the answers they seek. This is where a well-trained Allergist can use her detective skills to take a detailed history of the events leading up to the episode of hives and then decide, in partnership with her patient, what testing, if any, is needed.