Have you ever met a devoted cat-owner that is simultaneously allergic to that same cat? While 10-20% of the world’s population is allergic to cats or dogs, a 2020 survey of cat owners by the Human Animal Bond Research Institute found 23% of cat owners lived with an allergy to cats. 84% of those allergic owners preferred to seek alternatives to physician-recommended surrendering of their cats, such as through allergy management. While the reason behind pet ownership despite its obvious health challenges may be a testament to emotional bonds between humans and pets, it raises the question about the development of pet allergies.
Allergies and pet ownership in early life
Allergies are a broad group of hypersensitivities to seemingly harmless foreign substances. The most common symptom of these hypersensitivities is allergic rhinitis which consists of a runny nose, sneezing, hives, watery eyes, or itchiness around the face or area of contact.
Studies have reported correlations between increased pet exposure in the first year of life and reduced development of pet allergies. Additional studies have demonstrated decreased sensitivity to certain animals and general allergens in children living in a household with pets in the first two years of life compared to those who had never lived with pets. Further work studying the strength of the immune system of children living with pets is underway to understand whether these observations are causative. In the meantime, there is an absence of evidence suggesting that exposure to these harmless environmental agents could contribute towards allergy development.
Allergies and The Hygiene Hypothesis
The existence of allergies to common food items such as peanuts or eggs, and domesticated cats or dogs has stumped immunologists for many years. This went against the understanding of the immune system’s ability to distinguish harmful vs harmless foreign substances and react appropriately. That is, until epidemiologist Dr. David Strachan published his observations about the prevalence of asthma and eczema in 1989, leading to the development of a theory later called the hygiene hypothesis.
Briefly, the hygiene hypothesis suggests that reduced exposure to various microorganisms leads to deficient education of the immune system and a hypersensitive immune system later in life.
The foundation of the hypothesis is that changes in living conditions, such as better sanitation, improved barriers dividing the inside world from the outside world, and a reduction in the average family size, have led to less frequent exposure and infection by viruses, bacteria and parasites during one’s early years (0-3 yrs). While regular exposure to harmful parasites, and bacteria have been eliminated, exposure to harmless environmental substances such as pollen, and pet dander has also been reduced. Through mechanisms still being studied, the reduced repertoire of substances whose harmfulness was to be “learned” earlier in development has led to an ‘underdeveloped’ immune system. Later, when the immune system is exposed to these ordinary substances, it mounts very specific immune responses that are designed to target parasites (ex: histamine production). It is noteworthy that allergies are highly skewed to countries that are highly industrialized and are most impacted by the changes in living conditions.
Although not entirely irrefutable, the evidence for the hygiene hypothesis highly supports pet ownership during childhood and may provide parents with something to think about regarding the health of their children.
Sila Usta
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