Hello, After reading your query, it is likely that your condition is quite a common one referred to as physical urticaria (the scratching = physical) and itchy red rashes (= urticaria). But the urticaria you suffer also has another trigger: heat. That is why cooling the skin lowers histamine release. The above diagnosis is valid only if the itchy red weals disappear WITHOUT leaving any scrars or bruises. If you get this, a condition called urticarial vasculitis (= inflammation around blood vessels) needs to be excluded by skin biopsy + immunofluorescence studies. A blood test known as anti-C1q levels are sometimes useful as is the antinuclear antibody or thyroid peroxidase antibodies. High-dose non-sedating long-acing antihistamines (allegra 180/180)+/- leukotriene antagonists (montelukast 10mg)+/-anti-H2 (raitidine 150 twice daily) are usual treatment options in various combinations. Lot of other low grade immunosuppressants or immunomodulating drugs such as colchicine, dapsone are also good therapeutic agents but no blood test can dictate the choice of treatment. Rapid cure is sometimes possible but not permanent cure in most cases. I hope that was useful.