Migration remains a double-edged sword. Emigration can improve migrants' socio-economic circumstances through better education, higher income and by providing a safety net from persecution and violence. However, migrants remain vulnerable particularly in terms of poor health. Keeping migrants healthy is in the best interest of both destination countries and the countries of origin because of the bidirectional contributions they make towards them. Sadly, migrant health still remains an underresearched area in the health arena. This poses a challenge in gaining a better understanding of the causes of the health burden in order to develop effective prevention and intervention strategies to improve health among migrants. Due to poor understanding of the underlying causes of migrant health differentials, several hypotheses have been proposed including ‘healthy migrant effect’ and/or ‘Salmon bias’, for explaining migrant health advantage, and low socio-economic status, poor lifestyle and genetics for migrant health disadvantage relative to the host populations. Although largely untested, these hypotheses have become a standard ‘comfy zone’ explanatory model in migrant health research field. However, the reliance on these hypotheses have become a standing block for the development of the migrant health research field as they provide untested explanations in communicating their findings. To make progress in gaining better understanding on migrant health differentials, researchers need to move out of their ‘comfy zone’ explanatory model to test potential factors in the real world and to invest in other explanatory models such as the role of migration and the role of context. © 2019 The Royal Society for Public Health

Migrants ethnic minority groups Healthy migrant effect Explanatory model High-income countries

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