Urticaria (chronic hives) is one of the most interesting skin problems because most case causes go unidentified. Though there are several categories of causes (prescription medication, OTCs, foods, physical factors, immunologic and infectious), the reason behind 70-80% of cases is unknown.
In one recent case, a female patient related a 20+ year history of hives at different points in her life. Most of her incidences had occurred around pregnancy. Her hives had recently been acting up, and it turned out her implantable progesterone eluting IUD had been replaced a few months prior.
In medical literature and research, about 5% of women develop urticarial and even lip swelling (angioedema) in reaction to oral contraceptives. This female patient’s case may one of the rare instances where a cause was identified.
Bingham CO. New-Onset Urticaria. Saini S, Callen J, Feldweg AM, eds. UpToDate.