Hay Fever - Causes

Hay fever is a kind of immune reaction. The immune system consists of cells, tissues, and molecules whose job it is to fight off foreign invaders, such as bacteria and viruses. When a foreign substance enters the body, the immune system releases antibodies. Antibodies are chemicals with the ability to destroy the foreign substances.

In the case of hay fever, the immune system becomes confused. It treats dust, pollen, and other harmless substances as if they were dangerous invaders. Substances that cause this kind of reaction are known as allergens. The immune system releases antibodies against allergens the way it does against bacteria, viruses, and other dangerous substances.

The combination of antibody and allergen sets off a series of reactions designed to protect the body. These reactions cause cells and blood vessels to leak fluids. These fluids cause the familiar symptoms of hay fever, such as a runny nose, red and irritated eyes, an itchy nose, and a scratchy throat.

A substance that provokes an allergic response.
Increased sensitivity caused by previous exposure to an allergen that can result in blood vessel dilation (swelling) and smooth muscle contraction. Anaphylaxis can result in sharp blood pressure drops and difficulty breathing.
A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.
Small packets of reactive chemicals stored within cells.
A chemical released by mast cells that activates pain receptors and causes cells to that leak fluids.
Mast Cells:
A type of immune system cell that is found in the lining of the nasal passages and eyelids. It displays a type of antibody called immunoglobulin type E (IgE) on its cell surface and participates in the allergic response by releasing histamine from intracellular granules.

The number of possible allergens found in the air is enormous. Seasonal hay fever is most commonly caused by grass and tree pollen. Pollen is a fine powder by which plants are germinated. A number of weeds can also cause hay fever. These include:

  • Ragweed
  • Sagebrush
  • Lamb's quarters
  • Plantain
  • Pigweed
  • Dock (sorrel)
  • Tumbleweed

Perennial hay fever is also caused by a variety of particles found in the air including:

  • Body parts of house mites. House mites are tiny insects. They can be seen only with the aid of a microscope. They feed on fibers, fur, and skin shed by people who live in the house. When they die, their body parts get into the air.
  • Animal wastes. Animals constantly shed fur, skin flakes, and dried saliva. Common sources of these materials are pet dogs, cats, and birds. These materials easily get into the air. They cause allergic reactions in many people.
  • Mold spores. Mold is a fungus that grows in warm, damp places. It lives in basements, bathrooms, air ducts, air conditioners, refrigerator drains, mattresses, and stuffed furniture. Mold reproduces by giving off tiny seed-like particles called spores. These spores are released into the air. They can cause hay fever in many people.

Other possible causes of perennial hay fever include the following:

  • Cigarette smoke
  • Perfume
  • Cosmetics
  • Cleansers
  • Chemicals used in copy machines
  • Industrial chemicals
  • Gases given off by construction materials, such as insulation

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