Is prevention of childhood asthma possible? Allergens, infections and animals

What we know: Epidemiological studies have identified a number of factors associated with increased incidence of asthma. These include allergen sensitisation and exposure, reduced exposure to infections and to farm animals in early childhood, and maternal smoking. These factors may represent "true" risk factors for asthma or may be merely associated factors that do not in themselves cause asthma. The "hygiene hypothesis" has been proposed as one mechanism by which infections may protect against asthma. Current recommendations for the primary prevention of asthma include exclusive breastfeeding for the first six months of life, avoidance of maternal smoking during pregnancy and infancy, and reducing the levels of house-dust mite in some environments. What we need to know: What are the mechanisms by which specific risk factors and prevention strategies lead to or protect from asthma? How do genetic and environmental factors interact to increase the risk of asthma?