An allergen is an agent that can cause an allergic reaction. In some populations, the immune
system recognizes allergens as foreign or dangerous. Thus, the immune system reacts by making
a type of antibody IgE to defend against allergen and lead to allergy symptoms. Domestic animals
are one of the commonest allergen worldwide that children are sensitized. Commonest allergic
agents include: 1- Animal proteins and animal dander, 2- Insect bites and stings (their venom),
3- Insect and mite feces, 4- Insecticides, pesticides and repellents, 5- Crustacean shellfish
(e.g., crab, lobster, shrimp), 6- Pollen, 7- Drugs (such as antibiotics or medicines oral, injected,
inhalation or on skin), 8- Foods (such as egg, peanut, milk, nuts, soy, fish, animal meat, and wheat),
9- Fungal spores, 10- Dust (especially house dust mites, & 11- Natural rubber latex.