Allergic disease is still a serious global public health problem, affecting 30-40% of world population. The rapid increase in prevalence indicates gene-by-environment interaction, in which epigenetics may be the underlying mechanism. We reviewed recent epidemiological studies about the association between prenatal exposure to air pollution and childhood allergies. On the other hand, we reviewed the evidence that maternal exposure to air pollution caused epigenetic alterations that changed the gene expression or transcription in offspring. We further discussed the challenges of the global warming and COVID-19 to the childhood allergies especially in developing countries and suggested the opportunities to prevention or control by early intervention, immunotherapy, and epigenetic therapy.