It is a chemical in certain food items that causes allergic reaction. It should be noted that certain person are allergic to certain type of food while other person may be unaffected by such food items.

This statement is referring to food allergens. Food allergens are typically proteins within food that the immune system mistakenly identifies as harmful. When a person is allergic to a certain type of food, their immune system reacts to these allergens and can cause symptoms such as itching, swelling, hives, stomach cramps, vomiting, diarrhea, or even anaphylaxis in severe cases.

The reason why some people are allergic to certain foods while others are not is due to individual differences in immune system function. Some people's immune systems identify certain food proteins as harmful, while others do not. This is often genetically determined.

It's also important to note that just because one person is allergic to a certain food, it doesn't mean that everyone else will be. Allergies are highly individual.

In terms of managing food allergies, it's crucial to identify which foods cause allergic reactions and to avoid them. This often involves reading food labels carefully and being aware of potential cross-contamination in food preparation areas. In some cases, people with severe food allergies may need to carry an epinephrine auto-injector (EpiPen) with them at all times.

In conclusion, food allergens are substances in foods that can cause allergic reactions in certain individuals. These reactions are due to the immune system mistakenly identifying these substances as harmful. The best way to manage food allergies is to avoid the offending foods and to be prepared to treat allergic reactions if they occur.