Allergies are one of the fastest growing chronic diseases in childhood. The uptick may be due to lifestyle changes: As we spend more time indoors, exposure to allergens such as pets and dust mites increases. In the past 40 years there has been a dramatic increase in allergic conditions such as asthma, hayfever (allergic nasal symptoms), and food allergy, but not eczema, in the wealthier developed countries. The largest increase has occurred in the United States, United Kingdom, New Zealand and Australia. It is estimated that hayfever and asthma affect up to 40 percent of children, and some allergic manifestations may occur in as many as 65 percent of children in western populations. Children are selected for allergy studies because it avoids confusion with chronic infection, chronic obstructive lung disease (COPD), and symptoms due to cigarette smoke which are noted in adults. Allergic diseases are more common in urban vs. rural populations in the same countries and African Americans in the United States. Allergic food reactions have also increased significantly, but the true numbers are more difficult to determine because many children have food reactions which are not allergic.
It is commonly accepted that allergic diseases develop from environmental factors acting on genes in susceptible persons. One can have the gene to become allergic to cats, but if never exposed to cats, there will be no disease. It has been recognized for a long time that allergic diseases occur more commonly in the children of allergic parents. If both parents are allergic, children have a 50 percent risk of developing allergies. At the present time there is no single gene that has been identified that will predict if an individual will become allergic. Specific patterns, however, are associated with specific diseases. Eczema is primarily related to food allergic reactions. Allergic nasal symptoms are more commonly associated with allergic responses to pollen and outdoor molds.
Household Environmental Allergy Triggers
Asthma occurs more frequently in patients allergic to house dust mites, animals, cockroaches and the alternaria mold, a type of household mold. With house dust mites, the higher the exposure the more likely you are to develop the allergic antibody. Children with allergic parents require lower exposures than children from non-allergic parents to develop the allergic antibody. There does not appear to be a relationship between the amount of mite exposure and the development of asthma. With cat and dog exposures, the higher the exposure in the first year of life, the less likely are children to develop the allergic antibody or allergic diseases. These observations all indicate that many genes and complex environmental exposures are involved in allergic diseases.
It is now recognized that on exposure to foreign materials there are two major immune responses, the allergic and the protective response. Current evidence would indicate that by stimulating the protective response one can prevent and decrease the allergic response. The stimulation of the protective response before the development of the allergic response does not require knowing to what the child may become allergic and has been observed in a number of studies. High dog or cat exposure under one year of age can prevent the development of asthma, hay-fever or food allergies and the production of allergic antibodies to any allergen. The more infections and exposure to germs that children have, the less likely they are to become allergic. In several studies, there is less asthma in children who attend day care at ages 6-11 months vs. later. Older children in a family are more likely to have asthma than younger children, especially in larger families. This appeared to be related to more frequent infections in the younger children being exposed to older siblings with respiratory illnesses. In Italy and the Unites States, individuals with childhood hepatitis, toxoplasmosis or a specific stomach infection have fewer positive skin tests and allergic diseases. The same protection is also felt to explain the lower number of skin tests, asthma and allergic nasal symptoms in children growing up on farms. In these “dirty” environments there are more bacteria, bacteria products and parts, all of which are capable of stimulating the protective response similar to what is seen with infection and allergy vaccines.
Hygiene Hypothesis of Allergies
These observations have proposed the Hygiene Hypothesis as one explanation for the increase in allergies. It proposes that the emphasis on cleanliness has prevented the maturing of the immune response from an allergic to a protective response when faced with foreign substances. Pollen, mites, foods and molds are foreign but not harmful, and in the absence of a protective response the body responds with the allergic response. The Hygiene Hypothesis has also stimulated research to develop allergy vaccines which may be used in children of allergic parents to prevent allergic diseases and create more effective vaccines for children who show early manifestations of allergic symptoms. It has also decreased the emphasis on avoidance of foods and inhalants to prevent the development of allergic diseases. Once allergic however, avoidance is the best treatment.
Outside Environmental Factors
Another environmental factor contributing to the development of allergies is diesel fuel particles. Studies in Europe and the South Bronx have shown higher rates of allergic skin tests and asthma the closer you live to a major road and the Hunts Point Market. The Market is the largest in the world with diesel trucks being the major transportation of food products. Animal models demonstrate that diesel particles enhance the allergic response to pollen and outdoor molds.
Genetic Similarities of Obesity and Asthma
There are two epidemics occurring in developed countries. These are obesity and asthma, which are occurring in the same children and several mechanisms are postulated. One is that both share common genes. Another is that obese children are more likely to produce allergic responses then non-obese children. The third is that children with obesity and asthma have lower levels of Vitamin D3. This vitamin is also an antioxidant and may control the type of inflammation that occurs in allergic inflammation. Studies are being performed with Vitamin D3 in obese children with asthma and difficult to treat adult asthmatics. A simple treatment considered was exposure to sun to raise blood levels of Vitamin D3; this however was rejected by review boards because of the concern over skin cancer. We are fortunate to have good treatments for allergic diseases so mortality has decreased, but the cost to society and reduction in quality of life in individuals remains high. It is hoped as with other epidemics that improved allergy vaccines will be developed to prevent both disease and progression of disease.
Dr. John Condemi, Clinician, Allergy Asthma Immunology of Rochester