I think chronic hives are one of the toughest things that allergists routinely deal with. Chronic hives basically mean that the patient has hives (plus or minus swelling) more days than not for at least six weeks in duration. Often, patients come to me thinking they are allergic to something externally, such as a food, medication, or environmental trigger. The patient goes through a list of everything they have done, the last meal eaten before a hives a outbreak and/or commonalities between outbreaks. He or she often tells me they have changed everything to no avail like soaps, lotions, and laundry detergents.
This is the reality of hives: nothing external triggers them in almost all cases. There is no "allergy," per se. Rather, something internally is causing the allergy cells to go crazy intermittently and spontaneously release histamine and other allergic mediators resulting in hives. Oftentimes, especially in kids, it is an aberrant response to a viral infection that just takes time to work out. Sometimes, it can be an autoantibody that causes an autoimmune form of hives. Rarely, it can be low thyroid causing the hives. EXTREMELY rarely it could be hepatitis or even a way for certain forms of cancer to present. I used to perform a bunch of tests to help rule these things out but recently there was an updated practice parameter published on hives that suggested against this. Basically, these rare underlying causes of hives were in fact so rare that the current recommendation is not to perform these tests unless there is some other suspicion that the underlying cause might be something other than run-of-mill spontaneous chronic hives.
Eventually, the immune system almost always works the chronic hives out on its own. It might takes months or even years. But while we wait for this, we try and treat the hives with the goal of prevention to improve quality of life. Generally we start with second generation antihistamines that tend to last longer and are non-sedating. Older antihistamines such as diphenhydramine and hydroxyzine, interestingly, do not seem to be any better and in fact might be less effective for the treatment and prevention of chronic hives (with the possible exception of doxepin). For me, if high-dose antihistamine treatment fails, I move on to once monthly injections of omalizumab for chronic hives, which is expensive but highly effective. There are other options available for treatment of chronic hives, including immunosuppressive drugs, but these have more side effects and there is less evidence that they are effective. I always try to stay away from steroids if at all possible because for one there are obviously a lot of side effects, and secondly, once the steroid wears off "rebound" hives might appear that are even worse than before.
I always need to mention that chronic hives are a quality of life issue. They are uncomfortable, embarrassing, and interfere with daily activities. But one thing they are NOT is life threatening. There is an extremely low risk of the hives progressing to a life-threatening allergic reaction, so I almost never prescribe injectable epinephrine for these patients. The most important thing is for the patient and allergist to have a good working relationship with the ability to adjust things on the fly to get the hives under control and let the patient get back to living life as normally as possible.