Allergic parent have more chance to have allergic children than other children. Another factor of allergies is the body’s defenses are lowered or weakened so when they are exposure to the allergen, it is easier to provoke a reaction. This phenomenon always happens during pregnancy, puberty or after viral infection.
The immune system functions as the body’s defense help body to avoid from invading agents such as bacteria or viruses. However, sometimes this system is responding to false alarm. When the allergic person contact with an allergen, their immune systems treat the allergen as an invader and mobilize to attack. Immunoglobin E, or IgE is an antibody. Each IgE is specific for one allergen.
These IgE molecules attach themselves to the tissue cells and blood cells. When the enemy allergen next encounters the IgE, the allergen attaches to the antibody like a key fitting into a lock, signaling the cell to which the IgE is attached to release (and in some cases to produce) powerful inflammatory chemicals like histamines, prostaglandins, leukotrienes, and others. The effects of these chemicals on various parts of the body cause the symptoms of allergy.
MEDICATION: Using pharmaceuticals in various forms to block the symptoms of allergy. Necessary for asthma or 
severe nasal allergy treatment.
ALLERGEN AVOIDANCE: Depends on exposure of the allergy causing material and the substances. Less the allergic material you breath in or eliminating or decreasing your exposure to the substances to which you are allergic.
IMMUNOTHERAPY (ALLERGY INJECTIONS): The allergist give the first inject amount of allergen substances to which you are allergic to produce a degree of tolerance to them. And slowly increases the dose over time, thereby decreasing your degree of sensitivity.
It is under beds, inside sofas & carpet are creatures too small to see without a microscope. Dust mites are includes spiders, scorpions and ticks. Dust mites feed on dead skin from our bodies.
When you breathe in dust and you may have more serious symptoms. The symptoms are difficulty breathing or asthma attack.
Pet Dander
The most common household pets are cats, birds, rabbit and dogs. These pets dropping such as feathers, and other sources of bacteria, dust, fungi and mold, can increase the allergen exposure. Allergic person should not use feather pillows or down comforters.
Recommended pet allergy treatment - According to Allergists
Kept out the pets form room, if possible, outdoor. Allergic individuals should not pet, hug or kiss their pets. Isolating the indoor pet to one room and spread the allergen throughout the house by air-conditioning forced-air heating. Homes with forced-air heating and/or air-conditioning may be fitted with a central air cleaner with HEPA filters and heating to remove significant amounts of pet allergens from the home. It is the ways of reducing exposure to the pet allergen.
Cat Allergen
Cat allergen is particularly sticky. It is carried on clothing. The symptoms from allergens produced when the allergen become airborne as microscopic particles inhaled into nose or lung and it is almost impossible not to be exposed to some level of cat allergen. The levels of exposure will be much higher where cats are present.
Where are cat allergens found?
They are found mostly in homes where pets are present. and in places where pets have never been present, such as schools, workplaces, and other public spaces, brought to these places on the clothing of pet owners.
Mold
Molds are microscopic fungal organisms. They grow as networks of interlocking filaments that spread on and into organic matter, leading to its decomposition. When clusters of these filaments become large enough, they are visible as fuzzy growths of mold or mildew. Bread mold is a familiar example.
Mold lives by secreting enzymes that break down the organic matter on which the mold is living, making it available as a nutrient for the mold. Molds reproduce by forming spores, which travel through the air, settle on other plant or animal organic material, and grow into new clusters of filaments. The mold spores travel over large distances, and are often more numerous than the pollen grains of plants. Proteins in the secretions of the mold filaments, and possibly in the mold spores, are capable of causing allergy in some people.
Molds are found primarily in warm, dark, and damp locations. Unlike plants, which use energy from the sun to produce food, molds obtain their energy by digesting other organic matter. To do so, they need moisture. Molds grow out of doors, and, if the humidity is high enough, indoors as well. They can grow on grass and on the bark of trees, and are plentiful in fallen leaves and other decaying vegetation. Indoors, they live in areas of high humidity, such as basements or poorly ventilated bathrooms.
If you live somewhere humid, mold spores may be causing your dog's itching. Mold grows in a wet and moisture place. The itching follows the mold growth. If your house has ever flooded, or if the basement gets wet, you could be in for some nasty black mold called Stachybotros. In quantity, this mold can sicken and kill dogs, children and adults, too. Other, less toxic molds, such as Penicillium, are more common. Molds vary by region, but all may cause allergic reactions in people and animals.