It all started with a sandwich at 7-Eleven. Ada Cheng Suet-ngan was on holiday in Japan and grabbed a quick bite before rushing to catch a train in Osaka. Suddenly, she felt itchy and sweaty even though it was winter. She took off her jacket and saw rashes over her arm and neck. “I knew something was wrong, so I sat down, drank some water and tried to calm down,” says Cheng, recalling her first serious allergy flare-up in 2019. “I knew the station’s information centre must have an English...