According to the American Academy of Dermatology, hives in adults can be caused by many factors that include allergic reactions to shellfish, nuts and insect stings. Hives can also be brought on by stress and exposure to the sun and some chemicals.
Mayo Clinic explains that allergens, such as pet dander and pollens, and products containing latex can also cause hives in certain individuals. Underlying medical conditions that may trigger hives include hepatitis, thyroid disorders and immune system disorders. Individuals who undergo blood transfusions may develop hives in response to the procedure. Medications such as ibuprofen, aspirin, blood pressure drugs and naproxen may cause allergic hives in sensitive individuals. Mayo Clinic adds that risk factors for developing the condition include past allergic reactions and a family history of medical conditions in which hives are a factor.
WebMD reports that in certain cases, hives can appear with no underlying cause. Hives are also referred to as uticaria and present as itchy red swellings on the skin that range in size from small to large. Uticaria can develop anywhere on the body, including the tongue. In addition to itching, hives can sting or burn.
Hives that develop beneath the skin are referred to as angiodema, a condition that can cause severe swelling of the lips, hands, genitals and feet. Angiodema swelling typically dissipates within 24 hours, according to Mayo Clinic.