It isn’t clear why some people get asthma and others don’t, but it’s probably due to a combination of environmental and inherited (genetic) factors.

Asthma triggers

Exposure to various irritants and substances that trigger allergies (allergens) can trigger signs and symptoms of asthma. Asthma triggers are different from person to person and can include:

• Airborne allergens, such as pollen, dust mites, mold spores, pet dander or particles of cockroach waste
• Respiratory infections, such as the common cold
• Physical activity
• Cold air
• Air pollutants and irritants, such as smoke
• Certain medications, including beta blockers, aspirin, and nonsteroidal anti-inflammatory drugs, such as ibuprofen (Advil, Motrin IB, others) and naproxen sodium (Aleve)
• Strong emotions and stress
• Sulfites and preservatives added to some types of foods and beverages, including shrimp, dried fruit, processed potatoes, beer and wine
• Gastroesophageal reflux disease (GERD), a condition in which stomach acids back up into your throat

Risk factors

A number of factors are thought to increase your chances of developing asthma. They include:

• Having a blood relative with asthma, such as a parent or sibling
• Having another allergic condition, such as atopic dermatitis which causes red, itchy skin  or hay fever  which causes a runny nose, congestion and itchy eyes
• Being overweight
• Being a smoker
• Exposure to secondhand smoke
• Exposure to exhaust fumes or other types of pollution
• Exposure to occupational triggers, such as chemicals used in farming, hairdressing and manufacturing