as you said the outside food, Physical stimuli, such as pressure, cold, heat, exercise or sun exposure can cause this.better to avoid non veg particularly chicken,egg,prawns,seafood.can take manjishtadhi kashaya and patolamuladhi kashaya .apply dinesa kera on affected area before bath.
Next Steps
adviced to take ayurveda therapy like dhara,lepanam,virechanam etc.for better result.