This study measured how much debris is inhaled by infants when crawling on floors. Infants were found to be exposed to high levels of dirt, skin cells, pollen and fungal spores and received a dose of 'bio bits' in their lungs that was four times what an adult would breath walking across the same floor. Carpeted surfaces contained the most debris. Anatomically babies are not as good as adults at dealing with this debris. For adults a significant amount of biological particles are removed in the upper respiratory tract, while for infants a significant amount is deposited deep in their lungs Many studies have shown that inhalation exposure to a high diversity and concentration of microbes and allergen-carrying particles in infancy plays a significant role in both the development of, and protection from, asthma and allergic diseases. Therefore this early exposure may reduce the prevalence of asthma and allergies in later life.