My son is now 22. The first time this happened to my son was when he was around 16 years old after going through a lot of stress. Once he stopped stressing, we saw signs of the hair growing back. My son also has Chronic Fatigue, hearburn problems and ADD and has a type "A" personality. He is now starting to change his diet and started on probiotics and is starting to feel much better.
Regarding food allergies , he is very allergic to onions. That is the only one I really know of.