With her book Silent Spring, Rachel Carson was one of the first people to suggest that DDT was creating widespread problems in the environment. Although there may have been problems with the widespread use of DDT in the environment and some expression of concern was warranted, many of Carson’s claims were highly suspect and her extreme rhetoric led to an overreaction in the other direction—policies to curb DDT use even where it was most needed for public health purposes.

At the time, a reviewer of Silent Spring in Science magazine (September 28, 1962, p. 1043) praised Carson for raising concerns about potential dangers associated with pesticide misuse, but the author expressed serious dismay with Carson’s extreme approach. The reviewer noted: “Just as it is important for us to be reminded of the dangers inherent in the use of new pesticides, so must our people be made aware the tremendous values to human welfare conferred by the new pesticides. No attempt is made by the author to portray the many positive benefits that society derives from the use of pesticides. No estimates are made of the countless lives that have been saved because of the destruction of insect vectors of disease.”

Because of the anti-DDT and anti-chemical hysteria engendered by the ideas in Silent Spring, DDT was eventually removed from the market under the Nixon Administration. Yet DDT was banned despite findings of an EPA panel that it was not a public health threat. Barron’s magazine (November 10, 1975, p. 3) reported on the topic in 1975: “In banning DDT, for farm uses, then-EPA director Ruckelshaus over-ruled the federal hearings examiner Edmund Sweeney. After seven months of hearings, during which 125 witnesses were called and 9,000 pages of testimony were submitted, Sweeney declared that the evidence indicated that DDT wasn’t a cancer hazard. He added that on balance, its usage did not create an unreasonable risk with its benefits…‘In my opinion,’ he said, ‘the evidence in this proceeding supports the conclusion that there is a present need for the essential uses of DDT.’” Similarly, Barron’s reported, the year before the ban, the National Communicable Disease Center of the Department of Health, Education, and Welfare noted: “The safety record of for the use of DDT…is nothing short of phenomenal.”

The continued flow of misinformation about the public health impacts of DDT advanced by environmental activists along with the U.S. ban prompted public officials in other nations to stop using it and to even ban it in some places. In good measure, because of reduced use of DDT, malaria rates skyrocketed by the 1990s after having reached historic lows in the 1960s while DDT was in use. Roger Bate and Richard Tren note, for example, in Sri Lanka, which stopped using DDT in 1964, cases rose from a low of 17 to about half a million by 1969. Donald R. Roberts, MD, of the U.S. Uniformed Services University of the Health Sciences and his colleagues note: “Although many factors contribute to increasing malaria, the strongest correlation is with decreasing number of houses sprayed with DDT.” A study of malaria in Latin America demonstrates a causal link between DDT spraying and malaria rates.

This study also shows that when global efforts to control malaria began to reduce emphasis on vector control (i.e., DDT), the malaria problem grew. The authors reported that “countries that discontinued their house-spray programs reported large increases in malaria rates. Countries that reported low or reduced HSRs also reported increased malaria. Only Ecuador reported increased use of DDT and greatly reduced malaria rates.”

Despite the devastating toll associated with reduced use of DDT, many government agencies and environmental activists have been reluctant to change their views. Even where DDT is allowed, government aid agencies—including some at the U.S. Agency for International Development—have denied funding to nations if they chose to use DDT. In 1990s, the United Nations Environment Program began work on the Convention of Persistent Organic Pollutants (known as the POPs Convention), which set in place bans on 12 chemicals, including DDT. However, during negotations on this treaty, public health officials finally spoke out on the DDT issue, urging the governments to at least allow limited DDT use for malaria control. To that end, they signed an open letter urging POPs Treaty negotiators to include a public health exemption to the DDT ban. As a result, the final treaty allows for a temporary, limited exemption for DDT use for malaria control. But even with its limited, temporary exemption, the treaty regulations governing use make access more expensive.

In 2006, the World Health Organization decided that DDT use should again become an important part of malaria control programs, noting in a press release: “WHO actively promoted indoor residual spraying for malaria control until the early 1980s when increased health and environmental concerns surrounding DDT caused the organization to stop promoting its use and to focus instead on other means of prevention. Extensive research and testing has since demonstrated that well-managed indoor residual spraying programmes using DDT pose no harm to wildlife or to humans.”

Unfortunately, while DDT use has increased in some areas, particularly South Africa, where it is having positive impacts, its use is still limited in part by negative public perceptions about DDT and its risks.

DDT is among several tools used today to fight malaria in developing nations. Other tools include bednets, medical treatments, and other pesticides. However, DDT has proven to be most affordable and effective tool and for this reason should remain part of malaria control programs. In 1990, DDT was determined to cost two to 23 times less than other alternatives, and recent assessments find that it remains the most affordable insecticide (see: K. Walker, Cost Comparison of DDT and Alternative Insecticides for Malaria Control,” Medical and Veterinary Entomology 14, 2000: 345-354). Sadly, DDT prices have increased because of declining production, which is related to political campaigns to regulate and ban the substance.

As far as we know, the type of malaria that infects humans does not infect wildlife, which means the malaria parasite needs human hosts to survive. Accordingly, if human transmission could be prevented the malaria parasite would die off because of the lack of access to hosts. In most of developed world, public health officials eradicated malaria by preventing human exposure in large part through DDT programs. In addition, development also greatly reduced transmission of all types of mosquito-borne diseases because most people in developed countries now live in sealed homes—homes with screens and sealed windows that keep mosquitoes out. Air conditioning also plays a role because it enables people to keep windows closed.

In developing nations, controlling malaria is much more difficult because mosquitoes have greater access to the insides of homes. Mosquitoes enter homes—huts and other unsealed structures—freely and feed on people at night while they sleep. The use of insecticide-treated bednets can be helpful, but the benefits have been limited for a number of reasons: the nets are expensive, are often not used properly, can become damaged, and must be retreated or replaced relatively frequently. In addition, people often choose not to use them in hot climates because they reduce ventilation.

DDT is particularly helpful in these conditions, requiring limited applications where people live, rather than widespread application in the environment as was common in the 1950s and 1960s. Today, public health officials can spray DDT in and around huts and other residential structures to prevent human exposure in large part by repelling mosquitoes. In essence, DDT acts as a chemical “screen,” keeping mosquitoes away and killing the few that might enter homes. It also does not require that people do anything to make it work each night, and it’s relatively inexpensive. Because DDT is persistent (i.e., it does not break down quickly), it works a long time without the need of constant reapplication. Ironically, DDT is subject to regulations and bans around the world because of its persistence in the environment; yet this persistence is one of DDT’s key public health benefits.