Informal care is increasingly important in countries undergoing population ageing. Previous research has discussed how the long‐term care system may affect the behaviours of informal caregivers but has not paid much attention to how changes in caregivers' circumstances, particularly their health, affect those receiving their care. Using the Japanese Study of Aging and Retirement, we empirically examine how caregivers' health condition may affect the elderly parents receiving their care. We find empirical evidence that declining caregivers' health adversely affects care recipients' health. We see such links between informal caregivers and their in‐laws, demonstrating that these effects go beyond genetic influences.