Deet, a chemical found in most mosquito repellents, has been used for decades to ward off(防ぐ、近づけない)insects, but experts are now concerned that it could interfere with the proper functioning of the nervous system. While moderate use of the chemical is likely safe, researchers studying deet’s effects on rodents found that it interferes with the normal breakdown of acetylcholine (ACh), the most common neurotransmitter in the central nervous system. This results in a toxic buildup of ACh that ultimately prevents the transmission of signals from one neuron to the next. Though deet may not have the same effect on humans, the findings warrant further investigation.