Asthma results from complex interactions between an individual’s inherited genetic makeup and interactions with the environment. The factors that cause a genetically predisposed individual to become asthmatic are poorly understood. The following are risk factors for asthma:
- Family history of allergic conditions
- Personal history of hay fever (allergic rhinitis)
- Viral respiratory illness, such as respiratory syncytial virus (RSV), during childhood
- Exposure to cigarette smoke
- Lower socioeconomic status
- Exposure to air pollution or burning biomass
What are the different types of asthma?
Asthma may not be the same in different affected individuals. Asthma specialists currently use a variety of clinical data to categorize a patient’s asthma. This data includes the age of asthma onset, the presence or absence of environmental allergies, the presence or absence of elevated blood or sputum levels of eosinophils (a type of white blood cell), lung function testing (spirometry and fractional excretion of nitric oxide), obesity, and cigarette smoke exposure.
Types: T2 high or non T2 (T2 low)
Your doctor may refer to asthma as being “allergic” or “eosinophilic.” One or both of these characteristics make up a “T2 high” phenotype of asthma, which is the term for the type of immune inflammation associated with asthma. The allergic type typically develops in childhood and is associated with environmental allergies, which approximately 70%-80% of children with asthma have. Typically, there is a family history of allergies. Additionally, other allergic conditions, such as food allergies or eczema, are often also present. Allergic asthma often goes into remission in early adulthood. However, in many cases, the asthma reappears later. Sometimes allergic asthma can appear with elevated blood or sputum eosinophils. Asthma that develops in adulthood may be associated with sputum or blood eosinophils but without environmental allergies. Sometimes patients in this category also have nasal polyps, which are eosinophil-rich growths in the nasal lining.
Non T2 asthma, or T2 low asthma, comprises a smaller yet difficult to treat proportion of asthma that is not associated with allergies or eosinophils. This type of asthma is sometimes called “neutrophilic asthma” and may be associated with obesity.