Asthma is a breathing disorder characterized by inflammation of the airways and recurrent episodes of breathing difficulty. These episodes, sometimes referred to as asthma attacks, are triggered by irritation of the inflamed airways. In allergic asthma, the attacks occur when substances known as allergens are inhaled, causing an allergic reaction. Allergens are harmless substances that the body's immune system mistakenly reacts to as though they are harmful. Common allergens include pollen, dust, animal dander, and mold. The immune response leads to the symptoms of asthma. Allergic asthma is the most common form of the disorder.
An asthma attack is characterized by tightening of the muscles around the airways (bronchoconstriction), which narrows the airway and makes breathing difficult. Additionally, the immune reaction can lead to swelling of the airways and overproduction of mucus. During an attack, an affected individual can experience chest tightness, wheezing, shortness of breath, and coughing. Over time, the muscles around the airways can become enlarged (hypertrophied), further narrowing the airways.
Signs and symptoms
Signs and symptoms of asthma include the following:
- Shortness of breath
- Chest tightness/pain
What causes asthma symptoms?
People with asthma have sensitive airways that are inflamed and are ready to react to triggers that 'set off' symptoms. Although asthma is complicated, there are two main ways that symptoms can be set off:
- If you have allergic asthma, your symptoms are caused by an allergic reaction when you come into contact with an allergen (a substance that triggers an allergic reaction). Common allergens include pollen, pets and house dust mites.
- If you have non-allergic asthma, your symptoms are caused by an irritant you breathe in or another factor, but are not caused by an allergic reaction. Common irritants include cigarette smoke and car exhaust fumes. Common factors that can trigger asthma symptoms include exercise, cold weather, colds and flu.
It is possible that your asthma symptoms can be caused by allergic and non-allergic triggers, which means you can have both allergic and non-allergic asthma.