Allergic asthma is a common inflammatory condition that affects the small tubes that carry air in and out of the lungs, also called airways or bronchi. Airways of asthmatic individuals are generally more sensitive than normal and overreact to various stimuli. When an allergic individual with asthma comes into contact with a trigger (something that irritates the airway, i.e. pollen, dust, etc.), the lining of the airways becomes inflamed, the muscles around the walls tighten so that the airways become narrower and glands in the airways produce large amounts of mucus.
The prevalence of asthma is increasing. In 2009, 300 million people were affected worldwide. Approximately 5.4 million people in the UK are currently being treated for asthma. Approximately one in 11 children and one in 12 adults now have asthma.
How allergic reactions cause asthma attacks?
There are numerous mast cells in the airways of the lungs (blue dots). When they meet an allergen they release histamine and other chemicals that cause constriction and swelling of the airway. This results in asthma symptoms.
- There are different patterns of asthma. Some individuals have self-limited episodes followed by extended symptom-free periods. This is called intermittent asthma. Patients with seasonal allergic asthma have symptoms for longer periods of time and they are related to the exposure to seasonal outdoor inhalant allergens (i.e. grasses, trees, weeds, etc.). Patients with chronic or persistent asthma have daily or very frequently recurring symptoms. Usually their symptoms result in impairment of daily activities.
- Asthma has a variable course. Many children with asthma see it improve as they get older. But in some individuals, asthma persists into adult life. Whatever the course, however, asthma is virtually always controllable with acceptably safe measures.
The disease is characterized by variable and recurring symptoms due to airflow obstruction. The severity of the disease is variable and can range from trivial and infrequent in some – to severe, unremitting and dangerous in others.
Patients with asthma may have one or more of the following symptoms:
- Coughing. Repeated short cough that occurs most frequently during the night and early morning hours can be the first symptom.
- Recurring wheezing. Wheezing is a whistling sound that occurs when the airways are obstructed.
- Rapid breathing. During airway obstruction, asthmatic subjects may breathe faster than normal.
- Feeling breathless. Patients with asthma may gasp for breath.
- Chest tightness. Asthmatic subjects may refer the sensation of having a band tightening around the chest.
- Retractions. During airway obstruction, the ribs and clavicle may be more visible as the patient makes greater effort to inhale and exhale.
Asthma symptoms vary widely in young children. Cough is often the only symptom.
The cause of asthma is not well understood, but is it known that asthma often runs in families.
Parents with asthma are more likely to have children with asthma. If asthma is present in both parents, the likelihood of a child having asthma is even greater, but even then not all of the children will have asthma. Even among identical twins, both do not necessarily have asthma, although this is more likely than if they were just siblings or non- identical twins. This suggests that there is some additional factor that we do not yet fully understand, other than inheritance that influences the development of asthma.
A trigger is anything in the environment that causes the irritation, inflammation and narrowing of the airways. There are two categories of triggers: allergic (pollens, house dust mites, animal dander) and non-allergic (temperature, exercise, smoke, viral infections, combustion products, etc.).
Some risk factors for the development of asthma have been identified, such as the presence of other related allergic conditions (known as atopic conditions, i.e. eczema, hay fever, food allergy, etc); having bronchiolitis as a child; exposure to tobacco smoke as a child, particularly if your mother smoked during pregnancy; being born prematurely or with a low birth weight. Also, it has been suggested that differences in macronutrient and micronutrient dietary content could explain the increase in allergies.