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From your history it appears that, you are suffering from cholinergic urticaria or heat hives.
This condition of being hypersensitive or extremely sensitive to heat or the response of sweating. People with this condition often wonder why they feel itch when they exercise or any time they seem to get hot. It can be sensitivity to cold water also. Heat hives can occur at any age and can come and go often without treatment but in some it persists.
As you said, after exposure to hot or cold water the skin will become red and sometimes itchy lesions will appear. Itching or burning sensation during the initial attack is common, and normally goes away when the overall body temperature has cooled. No effective treatment is yet available to cure cholinergic urticaria except avoidance of trigger factors. Tablets like Levocetirizine or Desloratadine are only helpful for short periods. Avoidance of trigger should be your first priority. Oxyhive treatment is sometimes helpful.