Food allergies are different from food fads. Certain fds seem to have strange reactions on some people. Probably, you have come across a person who got skin rashes everytime he ate eggs. Certain substances in food cause "allergy" to some people. Allergy is the scientific name given to a disturbance which arises when a person is sensitive to a substance. Some people are allergic to pollen, others are allergic to skin-contact with some materials. Allergy to medicines is also common. In fact, before giving a penicillin injection, doctors first test whether the patient is allergic to it. Foods which cause allergies are, fish, eggs, milk and milk products. Substances that cause allergy are protein in nature. Food allergies are manifested in the form of skin rashes, skin eruption called eczema. asthma, frequent sneezing, one-sided severe headache called migraine, vomiting, diarrhoea, etc.