Wildfire smoke is no longer a regional environmental issue. It is becoming a nationwide public health challenge. Two large-scale studies from Mount Sinai School of Medicine, published in Nature Communications and Lancet Oncology, provide strong evidence that the source of pollution matters, not just the amount. They examined the effects of a fine particulate called PM2.5 that can penetrate deep into lungs and enter the blood stream. Authors say PM2.5 from wildfires was associated with greater health risks than the same particulate from non-wildfire sources. They say, taken together, the studies suggest wildfire smoke should be considered a distinct threat requiring mitigation beyond overall pollution response.