Jonathan Day, Ph.D, of the University of Florida Medical Entomology Laboratory, sticks his arm in a cage filled with mosquitos to demonstrate the effectiveness of repellents containing DEET.

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DEET Side Effects and Controversies

As wit­h most chemical compounds, DEET doesn't come without warnings or side effects. First, let's take a look at how DEET affects the environment.

The U.S. Environmental Protection Agency (EPA) reregistered DEET in 1998 to ensure it conformed to today's more stringent standards (rather than the 1950s standards). Because DEET is applied to the skin and not directly on plants or wildlife, its impact on the environment is minimal. However, the EPA shows DEET as slightly toxic to birds, fish and aquatic invertebrates. It's virtually nontoxic to mammals. The EPA currently rates DEET as Toxicity Category III, the second lowest of four categories -- or "slightly toxic" [source: EPA].

So, is DEET bad for you? The answer isn't totally clear. Overuse of DEET can have lethal consequences. Even so, data from 1961 to 2002 shows only eight DEET-related deaths. Three were from deliberate ingestion, two from dermal (skin) exposure and three were children receiving heavy and frequent applications of DEET [source: ATSDR]. The EPA stresses that DEET is perfectly safe when used in accordance with the directions on the label. Incorrect application can lead to health issues such as skin irritation, disorientation, dizziness and, in extreme cases, seizures or death [source: ATSDR].

You hear rumors that DEET causes cancer. This may partly be due to the fact that people confuse DEET with DDT, a known carcinogen. In truth, scientists have not established a direct link between DEET and cancer. The Centers for Disease Control and Prevention (CDC) classifies DEET as a group D carcinogen -- meaning it's not classifiable as to human carcinogenicity. In simple terms, that means that they can't say it causes cancer, but they can't say it doesn't, either.

For at-a-glance information, the activist group Beyond Pesticides keeps its own list of documented DEET health and environmental effects:

  • Cancer: Not documented
  • Endocrine Disruption: Not documented
  • Reproductive Effects: Not documented
  • Neurotoxicity: Yes
  • Kidney/Liver Damage: Yes
  • Sensitizer/Irritant: Yes
  • Birth/Developmental Defects: Yes
  • Detected in Groundwater: Yes
  • Potential Leacher: Yes
  • Toxic to Birds: Not documented
  • Toxic to Fish/Aquatic Organisms: Not documented
  • Toxic to Bees: Not documented

[source: Beyond Pesticides]