Allergens
Allergens are substances that can trigger an allergic reaction in some people. Common allergens that can cause respiratory conditions include pollen, dust mites, animal dander, and mold spores. Exposure to allergens can cause symptoms such as sneezing, runny nose, itchy eyes, and coughing. People with asthma or other respiratory conditions may experience more severe symptoms.Chemicals
Exposure to certain chemicals can cause respiratory conditions. Examples of chemicals that can cause respiratory conditions include gases such as carbon monoxide and nitrogen dioxide, as well as chemicals found in cleaning and industrial products. Long-term exposure to these chemicals can cause chronic respiratory conditions such as bronchitis and emphysema.Smoking
Smoking is a well-known cause of respiratory conditions. Cigarette smoke contains thousands of chemicals that can damage the lungs and airways. Long-term smoking can cause chronic respiratory conditions such as COPD (chronic obstructive pulmonary disease) and lung cancer. Secondhand smoke can also cause respiratory conditions in non-smokers.