Final answer:
Allergies occur when the immune system is hypersensitive to usually harmless substances known as allergens, leading to an abnormal and excessive reaction. This can result in a range of symptoms, from mild to potentially life-threatening. Genetics can play a role in one's susceptibility to allergies.
Step-by-step explanation:
Allergies result when the immune system is hypersensitive to antigens that ordinarily would not harm the body. The immune system in an allergic reaction overreacts to a substance that is typically harmless, known as an allergen. Common allergens include pollen, dust mites, mold, specific foods, insect stings, and certain medications. This reaction can be mild or severe, and in some cases, it may lead to life-threatening responses such as anaphylaxis.
Hypersensitivity is a condition in which the immune system reacts abnormally and excessively to an allergen, leading to a variety of symptoms. The tendency to develop these allergic reactions can be heritable, suggesting a genetic predisposition to hypersensitivities. While some individuals may outgrow their allergies, others may experience them ongoing throughout their lives.