Anti-DDT activists in the environmental movement often suggest we should stop using this chemical to save people from malaria and other diseases because mosquitoes will eventually develop resistance to the substance. However, a study published in the journal PloS One explains why such arguments make no sense. The study demonstrates that in addition to still being the most affordable product, DDT is likely the most effective over the long term because it repels most mosquitoes—keeping them from ever entering homes. These effects are critical for a couple reasons. First, mosquitoes are most active in transmitting disease at night as people sleep, so keeping these insects out of homes can reduce disease rates significantly. Second, DDT’s ability to repell remains intact—even for mosquitoes that develop resistance to DDT’s toxic effects. Accordingly, while DDT might kill fewer mosquitoes as resistance develops, it still prevents most of them from entering homes in the first place. The other two alternatives did not repel, and they are prone to resistance problems. Accordingly, once mosquitoes develop resistance to those products there is little to stop them from freely entering homes and transmitting disease. Hence, the authors note that that DDT offers the best chance of breaking the transmission cycle and controlling the disease. They urge others to consider the repellency benefits rather than toxicity alone before abandoning a very important tool in the battle against malaria and other serious illnesses.