The source of asthma is not fully understood. Healthcare professionals believe a combination of genetic and environmental factors determine whether or not a child becomes asthmatic. A child has a much greater chance of developing asthma when one or both parents have the condition.

Most experts believe that all cases of asthma develop in the first few years of life. However, although symptoms will often begin in infancy or childhood, sometimes they do not appear until adulthood. Several immune system theories have emerged on why more children than ever before are being diagnosed with asthma. One theory is that children are less exposed to certain types of bacteria and infections than in the past. Because of this lack of exposure, they do not develop the right types of immune cells to fight off potential infections.

To make up for this lack of immune cells, other types of immune cells (called TH2 cells) are produced. TH2 cells have been called the allergy cells, because they produce a specific type of antibody called IgE that causes both allergies and asthma attacks. Allergies and asthma are closely related; about 70 percent of people who have asthma also suffer from allergies.

Premature infants have a fourfold risk of developing asthma. Babies who have been exposed to cigarette smoke while in utero are also at increased risk.

Children with asthma are more likely to experience symptoms or full-blown asthma attacks when exposed to certain allergens and other factors classified as asthma triggers. These include:  

• Pollen
• Mold
• Dust
• Air pollution
• Pet dander
• Viral respiratory infections (e.g., colds, flu, bronchitis)
• Tobacco smoke
• Certain foods
• Exercise
• Aspirin or ibuprofen
• Cold air
• Temperature changes
• Perfumes and strong fragrances
• Aerosols
• Emotional stress
• Sinus infections
• Heartburn
• Sulfites (a preservative in salad bars, dehydrated soups, alcohol and other foods)

According to the National Institutes of Health, children who live in the inner city have disproportionately high rates of asthma. The cause of this is not completely understood, but contributing factors may include increased exposure to allergens, such as dust mites and cockroach debris, poor air quality and poor diet. It is known that these conditions can trigger symptoms in people with asthma. But whether such conditions may actually foster asthma itself has not been determined.