I. Increased exposure to perennial indoor allergens |
Increased time spent indoors (1955 to 1995) |
Improved conditions for mite and mold growth (1955 to 1975)* |
Decreased ventilation* |
Increased reservoirs for allergen (carpets/sofas) (1935 to 1965)* |
II. Changes in hygiene |
Clean water |
- Separation from sewage (1900)
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Eradication of helminths and malaria in Europe and United States (1920 to 1940) |
Decline in hepatitis A infection (1920 to 1990) |
Introduction of broad spectrum antibiotics (approximately 1960) |
Increased treatment and control of food to prevent bacterial infection (1900 to 1980) |
Immunization to control infectious diseases (1800 to 1990) |
III. Lifestyle changes: Secondary to the introduction of sedentary entertainment in homes |
Increase in the percentage of homes with television and increase in hours spent watching television (1955 to 1990) |
Decline in outdoor "play" (1955 to 1995) |
Rise in obesity (1970 to 2000) |
Changes in diet following changes in traditional family life (1965 to 2000) |
Decreased vitamin D levels secondary to decreased time spent outdoors and decreased intake |