What can cause hives and swelling if its not an allergic reaction?

Hives and angioedema. Most hives and angioedema are caused by allergic reactions however they can also be caused by reactions to medications or things like heat, cold or sunlight. A variety of infections, including viral or bacterial infections, or collagen vascular disorders can cause a very similar rash.
Many things. 1. Autoimmunity 2. Thyroid illness 3. Liver disease 4. Infection 5. Mastocytosis 6. C1 inhibitor deficiency causes swelling or deep hives. 7. Low protein levels cause swelling but not hives. 8. Ace inhibitors cause swelling and not hives from a non-allergic basis.
Mostly unknown. Also could be related to thyroid dysfuncton chronic lowgrade infections and rarely immune disorders.