Allergic rhinitis is usually triggered when an allergic individual comes into contact with proteins found in certain airborne particles. These proteins can come from a variety of sources, but usually include:

• Pollen. Small, powdery grains of flowering plants that can easily become airborne. These are most often produced by trees, grass and weeds.
  
  
• Mold and mildew. Tiny fungus spores that can become airborne. These often thrive outdoors in soil, vegetation and rotting wood. They can be found indoors as well, especially in damp areas, basements and bathrooms.
  
  

  

• Dust mites. Microscopic insects that inhabit household dust. They are often found indoors where there is less air circulation and on surfaces like carpets, bedding and stuffed animals.
  
  
• Animal dander. Tiny scales or particles from an animal’s skin. These very often come from a dog or cat.
  
  
• Cockroach debris. Droppings, eggs, saliva and small pieces of outer shell of cockroaches. These can be found indoors, even if an infestation of live pests is not currently a problem.

Like adults, children must be exposed to the allergen and sensitized to it before the allergy develops. Because young children often are exposed to indoor allergens such as molds, dust mites, dander and cockroach debris early in life, they may develop allergic rhinitis associated with these allergens in the initial stage of their lives.

As children grow older and spend more time outdoors, they are increasingly likely to be exposed to additional potential triggers for allergic rhinitis, including grass, tree and weed pollens that may trigger reactions once the child becomes sensitized to them.

Family history plays a big role in determining a child’s future allergy problems. Children are far more likely to develop conditions such as allergic rhinitis if they come from families with a known history of allergic reactions – whether or not the allergies are rhinitis-related. However, children who come from allergy-free families still can develop allergies.

First-born children appear more likely to develop allergic rhinitis than their peers, according to some research. Boys are more likely than girls to develop allergic rhinitis, but this evens out during adulthood. It also appears that children are more at risk for developing allergies if they are exposed to tobacco smoke and dusty environments early in life. The reason for such trends is not completely understood.