@joepie91 The general current consensus theory is that ADHD is neurodevelopmental, and its causes are mostly genetic. The only known single environmental factor with solid evidence behind it is lead exposure in early childhood, as in, before 2–3 years of age. (The count of Adverse Childhood Experiences is likely to get added to the list within foreseeable future; there's good studies about it, but political factors push back against recognising ACEs as medical environmental factors.) The supposed link between azo dyes and ADHD seems to be a misinterpration scare, particularly in that it's commonly used in scary stories about foods and drinks that teenagers might choose, and teenagers are long past the point where ADHD might develop or not develop.