What is Asthma?
Asthma is a chronic inflammatory disorder of the airways in your lungs that can make breathing difficult and limit physical activities [1, 2, 3, 4, 5]. Being inflammatory and constrictive, asthma narrows down and inflames the airways; therefore, wheezing, shortness of breath, coughing, and chest tightness become the usual symptoms of this chronic airways illness [6, 7, 8, 9].
During an asthma episode, inflammation leads to the lining of the airways swelling and the muscles around the airways tightening. Mucus fills the airways and reduces the air that can get through. Any of these ‘triggers’ can provoke an asthma ‘attack’, described as coughing and tightness in the chest [3, 4, 5].
Asthma is a chronic disease prevalent in about 334 million people worldwide [10]. It is estimated that 1 child in 12 has asthma in the United States, where it is the most common chronic condition among children [3, 4, 5]. However, asthma can also be developed later in life, known as adult-onset asthma.
What are the Causes of Asthma?
The exact causes of asthma remain unknown, but it is believed to result from a combination of genetic and environmental factors [11, 12, 13, 14, 9].
Recent work has implicated a genetic predisposition to the development of asthma. There appear to be several known gene markers associated with the development of childhood-onset asthma and those of atopic asthma. Genetics is only one of many asthma risk factors [14].
Other environmental factors are also important for asthma development. Exposure to allergens such as house dust mites, mold, pets, grass, tree and weed pollen, and allergens from pests such as cockroaches and mice can lead to allergic asthma [9].
Nonallergic asthma may be caused by irritants or triggers that are not allergens, such as cold air (especially rapid change from warm to cold), certain medicines, household chemicals, viral and bacterial infections such as the common cold and influenza, outdoor air pollution, and tobacco smoke [9].
Occupational asthma is caused by breathing in chemicals or industrial dust at work, while exercise-induced asthma happens during physical exercise, especially when the air is dry [9]. Other triggers include smoke, mold and mildew, air pollution, feather bedding, dust mites, cockroaches, animal dander or saliva, respiratory infections or colds, cold temperatures, dry air, emotional stress or excitement, and exercise [13].
However other conditions and life events can also predispose women to develop asthma: pregnant women can develop symptoms of asthma during their pregnancy and afterwards; at other times, although there are no asthma symptoms before then, the symptoms develop in some women during menopause. [13] Women of all ages over puberty may have the highest prevalence and severity of asthma, with the highest rates seen in women with early age at menarche and more pregnancies, leading to subcategories such as ‘menstrual asthma’ [14], and ‘pregnancy-induced asthma’, among others something that involves a female sex hormone component in asthma development.
Obesity is also believed to be a significant factor in the development of asthma, possibly because excess weight causes inflammation in the lungs and impairs their function. [14] Many lung infections, such as RSV or Chlamydia pneumoniae (CP), can increase your risk of developing asthma, especially if you get infected with the bug when you’re young [14]. Babies born prematurely are at an increased risk of developing asthma because premature lungs and breathing muscles can be handicapped [14].
What are Allergies?
When your immune system overreacts to substances innocuous to most people, the resulting bodily reactions triggered by ‘allergens’ are called allergies. Symptoms include a runny nose, sneezing, itching, rashes, oedema and asthma. The most severe allergic reactions (called anaphylaxis) require emergency treatment – and can be fatal in some instances [15].
What Causes Allergies?
No one knows precisely what triggers allergies, but they run in families, which suggests a genetic component. However, people don’t inherit specific allergies, only a general predisposition to experience them [16].
A key element of allergic reactions is that the body’s immune system reacts to a harmless environmental substance as if it were a pathogen. Common allergens include pollen, dust mites, mold spores, pet dander, foods, insect stings, and medications. Many people with allergies to one substance are also intolerant of more than one [17, 16, 15].
Environmental causes also contribute to allergy development; for example, the rise in pediatric asthma cases can be attributed to children spending more time indoors, increasing their exposure to indoor allergens [18].
Can Asthma Cause Allergies?
Asthma and allergies are very often comorbid conditions – they often occur together – but that doesn’t mean one causes the other. Asthma is a chronic disorder in which the airways of the lungs become inflamed, narrowing the airways. This causes the characteristic wheezing, shortness of breath and coughing. On the other hand, an allergy is an overreaction of the immune system to such normally harmless substances as pollen or dust mites. Allergies may manifest as sneezing, runny nose and itchy, red, watery eyes [16, 19, 20].
However, the two conditions are almost always inextricably intertwined. Allergies can trigger asthma symptoms or exacerbate established asthma. This type of asthma (aeroallergen- or allergy-induced, or ‘allergic’ asthma) is the most common type of asthma diagnosed in the United States, accounting for 60% of all US asthmatics [16, 19].
Exposure to allergens evokes an immune response, particularly inflammation and a narrowing of the airways, which characterizes asthma. Well-known allergens that can provoke allergic asthma include pollen, house dust mites, pet dander and foods [12, 20, 21, 22, 23, 24].
Conclusion
In conclusion, while asthma does not directly cause allergies, the two conditions are closely correlated, and allergies can trigger or worsen asthma symptoms.