An allergic response is a hypersensitive immune reaction to a substance that normally is harmless or would not cause an immune response in everyone. An

allergic Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, alle ...

response may cause harmful

symptoms Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

such as

itching An itch (also known as pruritus) is a sensation that causes a strong desire or reflex to scratch. Itches have resisted many attempts to be classified as any one type of sensory experience. Itches have many similarities to pain, and while both ...

inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...

or tissue injury.

Mechanism

Allergies are an abnormal immune reaction. The human immune system is designed to protect the body from potential harm and in people who have allergies the immune system will react to

allergens An allergen is an otherwise harmless substance that triggers an allergic reaction in sensitive individuals by stimulating an immune response. In technical terms, an allergen is an antigen that is capable of stimulating a type-I hypersensitivi ...

(substances that trigger an immune response). The immune system will produce

immunoglobulin E Immunoglobulin E (IgE) is a type of antibody (or immunoglobulin (Ig) " isoform") that has been found only in mammals. IgE is synthesised by plasma cells. Monomers of IgE consist of two heavy chains (ε chain) and two light chains, with the ε ...

, IgE,

antibodies An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...

for each allergen. The antibodies will cause cells in the body to produce

histamine Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 19 ...

. This histamine will act on different areas of the body (eyes, throat, nose, gastrointestinal tract, skin or lungs) to produce symptoms of an allergic reaction. The allergic response is not limited to a certain amount of exposure. If the body is exposed to the allergen multiple times the immune system will react every time the allergen is present. The reason why people get allergies is not known. The allergens are not passed down through generations. It is believed if parents have allergies the child is more likely to be allergic to the same allergens. Some common symptoms include itchiness, swelling, running nose, watery eyes, coughing, wheezing, trouble breathing, hives, rashes, mucus production, or a more severe reaction anaphylaxis. Allergic responses and the severity vary from person to person. Many substances can trigger an allergic reaction. Common triggers of a reaction include foods, likes nuts, eggs, milk, gluten, fruit and vegetables; insect bites from bees or wasps (often a severe response occurs); environmental factors such as pollen, dust, mold, plants like grass or trees, animal dander; medications or chemicals. Some people experience an allergic response to cold or hot temperatures outside, jewelry or sunlight. There are daily treatments to reduce the severity of the allergic response. Often these treatments include an antihistamine oral pill, nasal spray, or eye drops. Other treatments include an allergy shot, which keep the allergic response to a minimum. For more severe reactions an

epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands a ...

injection is carried around. This injection will be taken if the person is going into anaphylactic shock. The best treatment is avoidance of each allergen.

References

1) Allergies (2011) reviewed by A.D.A.M. A.D.A.M medical encyclopedia 2) Allergies.(2009) reviewed by Geimeier W J. Teen Health 3) Sicherer S, Sampson HA. Journal of Allergy and Clinical Immunology 2010 Feb 125 (2 suppl2) S116-25.

External links

Allergic response
entry in the public domain NCI Dictionary of Cancer Terms {{Authority control Symptoms and signs Allergology