Asthma attacks occur when a person with asthma (chronically sensitized or inflamed airways) is exposed to an allergen (a substance the body perceives as a threat, triggering an allergic reaction) or irritant that triggers a severe reaction. The airways constrict and begin to shut down, leading to symptoms such as shortness of breath, chest tightness, coughing and wheezing (a whistling or high-pitched sound that results when breathing tubes are narrowed or obstructed). Left untreated, an asthma attack can be fatal.

To understand how an asthma attack unfolds, it is important to know what takes place when a person breathes. Air is breathed in through the nose and mouth, and travels down past the vocal cords (larynx) through the windpipe (trachea). The bottom of the windpipe divides into left and right bronchi, the major air tubes that lead into the right and left lungs. The air continues on through the bronchi, which keep branching off like tree limbs into smaller and smaller air tubes known as bronchioles.

Eventually, these branches empty into millions of air sacs called alveoli. It is in the alveoli that the inhaled air finally crosses through tiny blood vessels called capillaries and into the bloodstream. Air travels through the blood to supply the cells with the oxygen they need to perform their work in the body. Meanwhile, the cells give up carbon dioxide into the blood, which transports it back to the alveoli. The carbon dioxide then moves into the lungs, where it is breathed out when a person exhales. 

A person without asthma has bronchial tubes with very thin walls that are surrounded by very loose smooth muscle. This allows the airways to open wide, making it easy for air to travel in and out.

However, the airways of a person with asthma are chronically inflamed and highly sensitive to allergens or irritants. Substances that would cause no problems in most people trigger a reaction in the lungs of people with asthma. This is a condition known as hyperreactivity. When the body is exposed to these triggers, it reacts by shutting down the bronchioles. The inner lining of the bronchial tubes, called the bronchial mucosa, contains two key elements involved in an asthma attack:

• Mucous glands. These usually produce just the right amount of mucus to keep the airways lubricated. However, during an asthma attack they produce too much mucus – flooding and blocking the airways.
  
  
• A group of cells – including eosinophils, lymphocytes and mast cells – known as “inflammatory cells.” These cells trigger inflammation in response to something the body perceives as a threat, such as allergens or irritants. The inflammation, in turn, allows for more blood to flow to the area, carrying cells to fight the threat. This is a natural system designed to protect body tissue, such as the lining of the bronchial tubes (mucosa). However, during an asthma attack, the tissues remain inflamed for extended periods of time.

The asthma attack begins when the immune system senses the triggering factor – which can be anything from pollen and latex to tobacco smoke and cold air – and overreacts in an attempt to protect the body. The inflammatory cells, which normally fight infections, rush into the lungs in what is known as an “inflammatory cascade.” 

These cells then release histamine, leukotrienes and other chemicals that cause the tissue in the bronchioles to become red, irritated and inflamed, which narrows the diameter of the airway in a process known as bronchoconstriction. As the tissues swell, they produce excess mucus that clumps together to form plugs that further clog the bronchioles.

Meanwhile, chemical mediators and nerves in the bronchial tubes cause the muscles surrounding the bronchioles to tighten in a process known as bronchospasm. This further narrows the airway inside, making it very difficult for air to travel through it. Although the people experiencing an asthma attack feel like they cannot breathe in enough air, in reality they cannot properly exhale, leaving air trapped inside the lungs. 

Every day 30,000 people across America have an asthma attack, according to the American Academy of Allergy, Asthma & Immunology. The factors that spark an asthma attack may be different for each person with the disorder. For some people, exposure to a single allergen is enough to induce an attack. Others need to be exposed to several triggers at the same time before they react.

Asthma attacks may start suddenly, or they may take days to develop. The severity of an attack also varies. Attacks can be mild, moderate or severe.