What makes people sick? Infectious agents like bacteria and viruses and personal factors like smoking, eating poorly and living a sedentary lifestyle. But none of these compares to the way that poverty makes us sick. Prescribing medications and lifestyle changes for our patients who suffer from income deficiency isn't enough; we need to start prescribing healthy incomes. The upstream factors that affect health -- such as income, education, employment, housing, and food security -- have a far greater impact on whether we will be ill or well. Of these, income has the most powerful influence, as it shapes access to the other health determinants.