METRO — People with asthma often fear the next attack. As a chronic inflammatory condition, asthma causes the airways to narrow and swell and produce extra mucus. This makes breathing very difficult, and also can cause wheezing and coughing fits, advises the Mayo Clinic.

Asthma is a common condition, affecting an estimated 26 million people, including six million children, in the United States alone. Despite that prevalence, the American Lung Association notes that the cause of asthma is unknown. Scientists continue to study asthma, focusing on various factors that may increase a person’s risk for the condition.

∫ Genetics: The ALA says genetics play a role, noting that the risk is higher among those with a parent or a sibling who has asthma.

∫ Allergies: Certain allergic conditions are linked to people with asthma. Seasonal allergies may compound asthma symptoms.

∫ Environment: Contact with allergens, irritants or even certain infections as an infant or in early childhood before the immune system matures is tied to asthma. Adult-onset asthma is often linked to exposure to chemicals or dust in the workplace.

∫ Infections: Respiratory infections as a child that caused inflammation and damage to the lung tissue are implicated in compromising lung function later on in life.

Once asthma is present, doctors often classify it as allergic or non-allergic, says the American College of Allergy, Asthma & Immunology. Certain allergens, such as pet dander or mold, can trigger a reaction in allergic asthma. For the non-allergic variety, stress, exercise, illness, extreme weather, and more may bring on an asthma attack.