These chemicals cause tissue damage and inflammation resulting in often dramatic symptoms, including allergic asthma, acute gastrointestinal distress, urticaria and anaphylactic shock, such reactions are potentially life threatening. Immune complexes are cleared from the system by white blood cells called macrophages. However, when there is an excessive build up of immune complexes, the macrophages are unable to clear them up quickly enough. Excess immune complexes are deposited in tissues causing injury and inflammation. Cell-mediated hypersensitivity occurs without the involvement of antibody or complement.
Contact dermatitis is an example of a type IV reaction.
Symptoms of type I hypersensitivity occur immediately, usually within an hour of eating the offending food. The reactions are violent and it is often obvious which food is the culprit. Certain food allergens are commonly associated with immediate reactions and include nuts, fish, shellfish, eggs, legumes and strawberries. Once sensitised the individual always remains allergic to the food. Fortunately these 'true allergies' affect only a small percentage of the population.