Nobody understands that there are some things that a person can’t eat for religious or health reasons.

In Japan, awareness of dietary restrictions is still quite low. Also, few shops are prepared to respond to allergy-related restrictions. Additionally, in many cases it is difficult to tell whether or not allergy-causing ingredients are in Japanese foods simply from how they look. For food products, ask the seller, or if it is a restaurant, ask the staff what kind of ingredients were used. There is also the possibility that language issues may be interfering with communication. If there are certain things that you absolutely cannot eat, it may be a good idea to have them written on a card in Japanese with the reason why you can’t eat them, and carry that around with you.