Study Details:

If you have reddish areas on your skin that are itchy or raised, you may be suffering from hives or welts, also known as urticaria. Urticaria can occur anywhere on the body including the face, arms, legs, chest, back, or face, and is associated with intense itching which can have a major impact on a patient’s well-being. Whenever your Urticaria (hives) has lasted for more than 6 weeks and occurs spontaneously, this is called Chronic Spontaneous Urticaria. Chronic Spontaneous Urticaria (CSU), also known as Chronic Idiopathic Urticaria (CIU) is defined as the spontaneous occurrence of itchy wheals (hives), angioedema (swelling) or both lasting for at least 6 weeks. Usually the cause of Chronic Spontaneous Urticaria cannot be identified but is often autoimmune, meaning the body’s own immune system is attacking the normal tissues of the body and causing hives as a result. 

References: https://www.aaaai.org/conditions-and-treatments/library/allergy library/hives-angioedema