Clinical Edge

Summaries of Must-Read Clinical Literature, Guidelines, and FDA Actions

Early-Life Environmental Asthma Risk in Children

J Allergy Clin Immunol; ePub 2017 Sep 19; O’Connor, et al

Higher indoor levels of pet or pest allergens in infancy were associated with lower risk of asthma among high-risk inner-city children, a recent study found. The study examined the relationship of prenatal and early-life environmental factors to the occurrence of asthma at aged 7 years among 442 children. Researchers found:

  • Higher house dust concentrations of cockroach, mouse, and cat allergens in the first 3 months of life were associated with lower risk of asthma.
  • Prenatal tobacco smoke exposure and higher maternal stress and depression scores in early life were associated with increased asthma risk.


O’Connor GT, Lynch SV, Bloomberg GR, et al. Early-life home environment and risk of asthma among inner-city children. [Published online ahead of print September 19, 2017]. J Allergy Clin Immunol. doi:10.1016/j.jaci.2017.06.040.


This study supports the incredible change in understanding of the development of allergic disease that has occurred over the last 10 years. Years ago, it was believed that we should protect young children from exposure to allergens so they would not develop allergic diseases like asthma because of early exposure. This has been proven to be incorrect. Many studies, including the study reviewed here, show that early exposure to allergens usually protects against the later development of allergic disease. For example, children exposed to farm animals in the early postnatal period where shown to have a lower risk of allergies and asthma later in childhood, and a similar effect has been seen with early exposure to pets.1,2 This is the “hygiene hypothesis” that originally postulated that the decrease in infectious burden that has occurred in modern society has contributed to the rise of allergic and autoimmune diseases.3 This has been extended to many allergens from cockroach dust to peanuts, where many early exposures have now been shown to decrease the later development of allergic disease. —Neil Skolnik, MD

  1. von Mutius E, Vercelli D.Farm living: Effects on childhood asthma and allergy. Nat Rev Immunol. 2010;10(12):861–868. doi:10.1038/nri2871.
  2. Fujimura KE, Johnson CC, Ownby DR, et al. Man's best friend? The effect of pet ownership on house dust microbial communities. J Allergy Clin Immunol. 2010;126(2):410–412. doi:10.1016/j.jaci.2010.05.042.
  3. Okada H, et al. The ‘hygiene hypothesis’ for autoimmune and allergic diseases: an update. Clin Exp Immunol. 2010;160(1):1–9. doi:10.1111/j.1365-2249.2010.04139.x.