In the 1940s, diseases such as malaria and epidemic typhus spread through arthropods like mosquitoes and lice. Chemist Paul Hermann Müller, who worked for a pesticide company, studied the insect-killing properties of the synthetic compound DDT. He demonstrated a “contact poison” mechanism: insects became paralyzed and died simply by touching the chemical, without needing to eat it. A key feature was its residual action; after a single spray, the effect could last for weeks or even months. During and after World War II, DDT was used for indoor residual spraying and drastically lowered malaria incidence in many regions. Later, concerns over environmental contamination, bioaccumulation, and insect resistance led to strict regulations, but at the time the discovery saved countless lives. This life-saving impact formed the basis of Müller’s Nobel Prize.

DDT (dichlorodiphenyltrichloroethane) is a lipophilic organochlorine insecticide synthesized by condensing chlorobenzene with chloral. Screening more than 500 compounds, Müller reported in 1940 that DDT exhibited unmatched insecticidal spectrum and long residual activity. In his assays, low concentrations of a few ppm caused over 90 % mortality in mosquitoes, flies, lice, and fleas – the principal vectors of human disease. The compound targets voltage-gated sodium channels in insects, preventing channel closure, blocking repolarization, and inducing continuous neuronal firing that leads to death. Because of its contact toxicity, DDT did not need to be ingested; it could be applied as indoor residual spraying (IRS) over large surfaces. In 1955 the WHO launched the Global Malaria Eradication Programme, with DDT as the core tool. Malaria elimination was achieved in the Caribbean, parts of Asia Minor, and the Balkans, while in tropical Africa the rise of resistance limited success. From the 1970s, environmental persistence and biomagnification highlighted by Rachel Carson became central to policy debates, and agricultural use was banned in many developed countries. Nevertheless, in historical context DDT is regarded as a landmark compound that revolutionized insecticide development and disease-control strategies.

In Müller’s original work he compared the o,p' and p,p' isomers and quantified the influence of electron-withdrawing substituents on contact toxicity. He reported that a glass plate treated at 1 mg m⁻² retained an LD₉₀ for more than 90 days at 25 °C and 60 % RH, demonstrating unrivaled residual performance. Subsequent electrophysiological studies implicated binding to an allosteric site in the II-S6 segment of the insect Nav channel α-subunit as the primary mode of action. DDT-induced prolongation of channel open time, together with steric differences in mammalian channels, accounts for its insect-selective toxicity. High lipophilicity facilitates cuticular penetration and reservoir formation, delaying induction of detoxifying enzymes such as P450s and GSTs. The discovery accelerated SAR analysis of halogenated organics and guided the later synthesis of organophosphate and pyrethroid classes. However, DDT exerts strong selection pressure for resistance, including kdr mutations and metabolic detoxification; modern Integrated Vector Management (IVM) therefore relies on rotations and mixtures. Under the Stockholm Convention on POPs, DDT is restricted but allowed for public-health IRS; WHO-PQ benchmarks require formulations with ≥ 80 % p,p'-DDT. The 1948 Nobel Committee did not yet consider environmental toxicology, and the cost-benefit debate over DDT continues today. Müller’s work exemplifies the need for multidisciplinary evaluation in chemical innovation.