Name a major factor that predisposes children to respiratory infections.

The major factor that predisposes children to respiratory infections is the combination of an immature immune system and exposure to pathogens. Children, particularly infants and toddlers, are still developing their immune defenses, making them more susceptible to infections. Their immune systems have not yet been fully exposed to various pathogens that adults may have encountered and built immunity against. Consequently, when children are exposed to viruses and bacteria, their bodies may not mount an adequate immune response, leading to an increased likelihood of respiratory infections.

While the presence of allergies and asthma, the use of antibiotics and vaccines, and exposure to secondhand smoke can also play significant roles in respiratory health, they do not single-handedly predispose children to infections in the same fundamental way that an immature immune system does. Allergies and asthma can cause complications and exacerbate respiratory issues, and while antibiotics can help combat infections, overuse can lead to resistance. Vaccines enhance immunity but do not directly link to increased susceptibility. Secondhand smoke can harm respiratory health, but it is the immature immune systems of children that primarily create a higher risk for initial infection during their early years.