INTRODUCTION: The epidemic of allergic disease is a public health crisis, particularly for children in developed countries. Recognized effects of vitamin D in immune development have given credence to the hypothesis that changing patterns of human behavior associated with declining sunlight exposure may be linked to the rising immune and inflammatory diseases. Although data to support this are still limited and heterogeneous, vitamin D supplementation in early life is recommended to prevent vitamin D deficiency in many countries, raising important questions around safety and benefit for immune development and implications for allergic risk. AREAS COVERED: This review article examines the evidence of the impact of in utero and postnatal vitamin D exposure on allergy risk in childhood. Evaluated are relevant studies from 2007 to June 2014. EXPERT OPINION: Information on the impact of vitamin D on rising rates of allergic diseases is largely based on observational studies with conflicting results. There is an urgent need to conduct well-designed randomized controlled trials to address the significant uncertainty in this field. Additionally, the effects of other potential immunomodulatory factors associated with sun exposure (such as UV light) need to be examined further.