Allergy to seafood is one of the most common food allergies for people at all ages. There are three types of seafood: crustaceans mollusks and finned fish. Unlike some other food allergies, once a person has developed an allergy to seafood it is likely to be with them for the rest of their lives. An estimated 7 million Americans have some sort of seafood allergy, whether to fish, shellfish, or both. Approximately 60% of those with fish allergies and 40% of those with shellfish allergies have experienced them since childhood. Although a seafood allergy can develop in adults at any time, it most commonly appears between ages 40 and 60. Though shellfish allergy is the most common allergy to seafood, the precentage of shellfish allergy for adults is 2.5% and 0.5% for children, allergy to finned fish is also a common food allergy. Percentage cover of allergy to finned fish is around 1% of the whole population, and it is more likely to occur in adults than in children. Among children with allergy to finned fish, the allergy is typically a life-time disease. Moreover, the development of allergy always occur when they grow up, and these individuals are also impossible to completely sovle their allergy. Since the allergenic protein parvalbumin(which will be mentioned afterwards) in finned fish is similar amongst all types of fish, rmore than half of people who are allergic to finned fish are also allergic to other types of fish. Fish is made up of proteins and some other organic substances, so actually the allergy to fish is the allergy to those particular proteins. The main foreign proteins causing fish allergy are called parvabumin and Gelatin, parvabumin is responsible for balancing the Ca2+ ions in the fish and gelatin is derived from collagen obtained from animal body parts. However, parvalbumins are similar in between different types of fish, so this can explains if a person gets allergic to one type of fish, he/she should avoid all kinds of fish because almost all of them can cause allergy to him/her. Also, other type of fish allergy is caused after eating excess amount of fish, the large amount of proteins which will then convert into histamine when enters human body. Histamine can increse the brittleness of capillary, the permeability goes up the small blood vessels expand and the surrouding skin become red and swell up; it can also affects nerves in skin, causing itchiness and increase the amount of mucus produced in nose lining which in turns, cuaing itching and burning sensation. Some people were born without some kinds of enzyme which are responsible for breaking down the histamine. As a result, when those people have eaten excess amount of fresh fish or seafood, they took in large amount of histamine which the body won’t be able to decompose, and some allergic symptoms will appear. For those people, they can choose to take a medicine called antihistamine to remit the symptoms.The book ‘ Food Allergies For Dummies’ indicates that the best tests for allergies are skin tests, RASTs. After these tests, the doctor will ask the patient to keep a food diary which is the listing of food and drink tha patient takes in. It will be useful in identifying overlooked foods, hidden ingredients and differet types of reactions. Then it is the diagnostic elimination diet for avoiding allergy: it just simply removes some particular foods or food groups from the diet to see if the symptoms will disappear. However, this diet has some drawbacks such as lack of essential nutrients for growth of child.In the past, allergy was present, however, people didn’t realize that they actually had allergy to certains types of fish, some of them knew when they eat fish they would have rash, nausea or even vomitting but they don’t know what it was. And the duration and symptoms are the same, the only difference was ancient people did’t take any medicine when facing with allergy because those kinds of medicine haven’t been developed at that time. So no traces for comparision between ancient and modern fish allergy.Expert always suggest those who have a fish allergy avoid any type of contact with fish which is the mainstay of treatment for fish allergy. This includes avoiding fish restaurants, fish markets and anywhere fish is being cooked. There is a high risk of cross-contamination in the kitchen of a seafood restaurant, even if ordering a dish that does not contain fish. And the proteins in fish that cause allergic reactions may become airborne as it is cooking. An allergen can enter the body by consuming a food containing the allergen, and can also be ingested by touching any surfaces that may have come into contact with the allergen, then touching the eyes or nose. Fish is used for flavoring a variety of prepared foods, so people are advised to read the labels on any products bought in the supermarket to ensure that they do not contain any fish. Although fish oil supplements may seem like something to avoid, many people with fish allergies have no reaction to these supplements. However, first check with doctor to ensure that it is a safe option.the conclusion Overall, according to those knowledges related to immune system, those harmless proteins such as parvabumin and gelatin actually have foregin antigens in the cell surface membrane, which will be in turns, treated as threat to our body, trigger immuse response like the release of different numbers of chemicals, like the activation of B-lymphocytes to release plasma cells and memory cells, killer T-cells for undergoing and phagocytes for process of phagocytosis by helper T-cells. Plasma cells then manage to produce some antibodies against these foreign proteins. Everytime the foreign proteins inside fish enter body, the antibodies were produced and a chain of chemical reations is triggered, which will cause some severe symptoms like rash.