Dust mite micro photograph

Relevance of Indoor Allergen Exposure

The prevalence of allergic diseases, including asthma and hay fever (allergic rhinoconjunctivitis), has increased in developed countries around the world during the past decades and continue to increase. According to the American Academy of Allergy Asthma and Immunology, allergic diseases currently affect more than 25% of individuals in the USA. This has impacted the global allergy market.

Many studies suggest that exposure to common indoor allergens is a relevant environmental factor partially responsible for the increase in prevalence of allergic diseases in developed countries. Individuals in these countries spend more than 90% of their time indoors, and therefore exposure to indoor allergens is prolonged. Genetically susceptible individuals exposed to indoor allergens, primarily during infancy, become sensitized to these allergens.

Allergen avoidance can prevent (to some extent) the development of sensitization to allergens and relieve allergic symptoms in allergen-sensitized individuals. Therefore, various medical and public-oriented professional organizations have emphasized the relevance of indoor allergen exposure and recommended several guidelines for affected subjects, encouraging the use of certain measures for optimal indoor allergen avoidance.

Several multi-center studies on asthma and allergens performed at the national level in homes of affected subjects (including the National Cooperative Inner-City Asthma Study and the National Survey of Lead and Allergens in Housing) have demonstrated the usefulness of allergen measurement in monitoring the efficacy of allergen avoidance interventions.

The high prevalence of allergies has contributed to the increased public concern about air quality in homes, schools, and the workplace during the past years. However, due to the growing demand for mold assessments, common allergens (other than fungi) are not typically addressed during the course of indoor air quality inspections, albeit these non-fungal allergens are often the cause of the allergy symptoms experienced by building occupants.

A number of allergens are present indoors. A dose-response relationship between exposure and sensitization has been described for dust mite, cockroach, cat, and dog allergens. Cat and dog allergens are contained in small particles (2-6 um in diameter), which  are passively transported to public buildings. Therefore, cat and dog allergens are ubiquitous and present in the majority of buildings, including those where these animals have never been housed, like new homes and schools, at levels that, in some cases, exceed proposed thresholds to cause sensitization.

Studies performed in several major inner cities of the USA have linked exposure to cockroach, rat, and mouse allergens with asthma, and indicate that these allergens account for 95% of the allergen load present in some homes.

The relevance of indoor allergen exposure during infancy to cause sensitization and development of asthma should be emphasized to the general public. Daycare centers and schools can be critical sites of exposure to indoor allergens, and it has been suggested that these buildings should be target locations for interventions. Epidemiologically, it can be more effective to target one single daycare center or school than multiple homes.

How Human Activities Impact Pollen

A large number of plants exist on Earth. Geographical location, soil composition, and climate are the main natural factors associated with plant distribution and botanical biodiversity. Speciation and hybridization are responsible for the existence of different plant varieties of the same species, which often produce pollen with allergenic capacities composition. Pollen is responsible for seasonal allergies worldwide.

The topic of how human activities impact pollen is complex. Urbanization alters the distribution of native plants by reducing their ecological niches. On the contrary, plants that produce highly allergenic pollen are often introduced in urban areas due to landscaping practices.

Invasive plants are also accidentally introduced in ecosystems, and they slowly replace native plants.  For example, short ragweed (Ambrosia artemisiifolia), a weed native from the USA that produces highly allergenic pollen, was introduced in Europe years ago, and now this pollen is responsible for seasonal allergies in many European countries.

“Global warming”, another phenomenon associated with human activities, also affects plant biodiversity. A global increase in temperature is altering the geographical distribution of many plant species and their pollination patterns.

In addition, to the effect of human activities on pollen previously mentioned, this phenomenon might also impact pollen directly. For example, many observations indicate that the increasing levels of air pollution associated with urbanization and extensive use of fossil fuels augment the allergenic potential of pollen derived from different plants. Other observations suggest that pollen exposed to high levels of air pollution have greater inflammatory properties than pollen present in non-polluted areas.

In summary, the effect of human activities on plant biodiversity, pollination patterns, and pollen allergenic potential has been documented. The potential impact of this phenomenon on human health is under investigation.

Allergists/immunologists should be aware of the potential impact of human activities on pollen, and that their patients could perhaps experience non-expected exacerbations of their allergy symptoms in the future. Companies that manufacture pollen allergen extracts to diagnose and treat allergic diseases should take the correct measures to assure that the appropriate pollen is collected for the intended purpose.

Factors Responsible for Allergies

According to the World Health Organization (WHO) and the World Allergy Organization (WAO), allergies or immediate-type hypersensitivity reactions, affect approximately 20-30% of the world population. Allergies are the most common chronic diseases in adults and children in developed countries, accounting for high levels of morbidity and social burden, as determined by various direct and indirect parameters. These parameters include self-reported symptoms, medication use, hospitalizations, emergency room admissions, and missed work or school days.

The prevalence and incidence of allergies has increased during the past decades and continue to increase in developed countries.  Several hypotheses, including the “Hygiene Hypothesis”, have been proposed to explain this phenomenon. This hypothesis postulates that the decreasing exposure to microbial products, resulting from civilization, plays a role in switching Th1 to the Th2 immune response. Th1 responses protect from developing allergies while Th2 responses promote them.

Many individuals in the world live in urban areas, which have grown during the past years. Developing countries are evolving, an over 90% of urban growth is occurring in those nations, adding an estimated 70 million new residents to urban areas each year. Therefore, an increase in the prevalence and incidence of allergies in developing countries should be expected over time.

Multiple factors responsible for allergies have been identified. The factors responsible for allergies are complex and result from a combination of both genetic and environmental components.

Allergies cluster in families. The risk of developing allergies in children is estimated to be around 30% if one parent has allergies and 70% if both parents suffer from them. A large number of genes have been associated with allergic asthma and particular allergic phenotypes.

The most important environmental factor responsible for allergies is exposure to allergens. Other environmental factors that can promote allergic sensitization and trigger symptoms, particularly asthma, include exposure to air pollutants.

Infants with particular genetic phenotypes predisposing to allergies initially develop food allergy, resulting in atopic dermatitis, which generally resolves with increasing age. It has been reported that approximately 40%-70% of those children are symptom-free when they reach an age of approximately 7 years.

In many cases, children with food allergies subsequently develop allergic rhinitis, resulting from exposure to aeroallergens. Allergic rhinitis often evolves to allergic asthma. This progression in the manifestation of allergic symptoms is known as “the allergic March”

Due to the complex interaction among the various factors responsible for allergies, a number of long-term birth cohort studies have been and are being conducted to ascertain the relevance of the combined factors responsible for allergic sensitization and its progression from childhood to young adulthood. These studies include the  International Study of Asthma and Allergies in Childhood (ISAAC), Mechanisms of the Development of Allergy (MeDALL), Developing a Child Cohort Research Strategy for Europe (CHICOS), Environmental Health Risks in European Birth Cohorts (ENRIECO), and Global Allergy and European Network (GA2LEN). These studies will identify the factors responsible for allergies.





Pollen and fungal spores

Outdoor Allergen Exposure

Outdoor allergen exposure, particularly pollen, and to a lesser extent fungal spores, cause seasonal allergies to many individuals worldwide. While it is not possible to totally avoid exposure to those allergens, it is feasible to minimize it. For this purpose, it is important to be aware of the types and levels of airborne pollen and fungal spores present outdoors day-to-day during various seasons of the year in different geographical locations.

The National Allergy Bureau (NAB), founded in the early 1960s, is a section American Academy of Allergy Asthma and Immunology dedicated to distribute pollen and spore counts nation wide. For this purpose, a number of certified stations collect outdoor air samples and provide pollen and spore count data to the community. Those data are included in the NAB web site and distributed to the public.

Other organizations in the world, for example, the British Aerobiology Federation in the United Kingdom, are analogous in scope to the NAB. Those organizations also report regular pollen and spore counts to the public. In addition, they promote the science of aerobiology at different levels.

Pollen and spore counting and identification are a time-consuming task to perform that requires a high level of expertise. The fast pace that modern society operates, together with the perception that the technology currently used to perform the counts and identification has not changed in many years, has contributed to a decline in the interest of young individuals to learn about the complex area of aerobiology.

To partially overcome the caveat mentioned above, various companies are developing systems and equipment to automate particle counting and identification to the best possible extent. Current efforts in that regard indicate that while automatic particle counting is feasible, proper identification of the particles is very challenging to perform using automatic approximations. Side-by-side comparisons of the pollen/spore counts and identification determined using automatic systems and by optical microscopy should be performed to validate and optimize technology.

Another benefit of the data derived from the completion of aerobiological surveys is to assist pharmaceutical companies conducting clinical trials that involve subjects with seasonal allergies. The purpose of these trials is to ascertain the safety, efficacy, and doses of particular medications or immunotherapy formulations before they can be marketed.

To conduct those clinical trials, individuals sensitized to particular outdoor allergens are selected and allocated into various groups, receiving either an active treatment or a placebo before or during particular pollination seasons. However, due to the limitations associated with natural exposure to outdoor allergens, environmental chambers are being developed and validated to perform exposure challenges under controlled conditions. While this approximation is optimal for the purpose of licensing and marketing particular products, it does not reflect the types and levels of exposure to outdoor allergens that individuals experience under natural conditions, which is ultimately responsible for sensitization and allergy symptoms.


Global Warming and Allergies

“Global warming”, also referred as to “climate change”, is a subject that has received major attention during the past years. The concept of global warming popularly used now refers to a gradual raise in the global ambient temperature that began in the 19th century, parallel with an increase in levels of air pollutants resulting from human activities, associated with industrialization and the use of fossil fuels. Climate change refers to climatic alterations over extended periods, often millennia.

While the real occurrence of global warming has been debated, the Intergovernmental Panel on Climate Change prepared an extensive report, which supports that global warming is occurring. Direct data indicates an increase in the levels of atmospheric CO2 parallel with an increase of the global surface temperature over time. Changes in rainfall patterns have accompanied the detected temperature increase.

Climate change has been reported to affect ecosystems. Warmer temperatures have altered the geographical distribution of many plant species and their pollination patterns. For example, ragweed pollinates earlier now than in the past and produces larger quantities of pollen in urban vs rural areas. Indirect evidence suggests that allergic individuals could suffer more severe and frequent exacerbations of the disease in the future.

While the proposition that global warming could indirectly affect allergic individuals has gained a lot of media attention, this hypothesis needs to be evaluated by conducting long-term epidemiological studies, which should include the analysis of potential confounding factors. The potential connection between global warming and allergies should be an area of research involving multi-discipline groups.