Skin Allergy. Could be the exact reason?

Two years ago my father used to get severe rashes on his skin during the month of summer, he stays in Nagpur, when consulted a homeopathic doctor he said that its due to eating something sour and some medicines were prescribed, the rashes would go temporarily. This summer the situation got worst and rashes had become severe and water used to flow from his face. For immediate relief the we consulted an allopathy doctor who gave some medicines and told the reason that its due to the extreme sun conditions, he has also given a warning that the medicines could develop diabetes. The rashes subsided in three days. Two months later we conducted all tests(blood, lipid profile,etc) to clear our doubt, it came clean, he doesn't have diabetes or sugar or any other ailment, the doctor has given the same reason that it must have happened due to extreme weather conditions. Now a month ago his left face got swollen. What could be the exact reason?