Insecticides help control insects in the home garden or landscape. But, insecticides contain dangerous chemicals that are dangerous when misapplied, spilled or disposed of improperly. Follow the safety and application instructions on the packaging label of insecticides to prevent bad effects to yourself and the environment.

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Spray insecticides when there is little chance of rain and no wind to prevent the chemicals from drifting.

Allergic Reaction

An acute allergic reaction can occur within 24 hours of exposure, according to the University of Missouri Extension's website. Allergic reactions usually include difficulty breathing similar to an asthma attack, skin and nose irritation and watering of the eyes. Allergic reactions do not occur in all people who use pesticides, even in some people who are sensitive to chemicals.

Chronic Poisoning

A person who is exposed to small amounts of insecticides over a long period of time can experience the effects of chronic poisoning. This type of insecticide poisoning often causes physical and neurological effects such as nervousness, slow movement, twitching and a decline in good health. Chronic poisoning may be difficult to treat, especially if the source of the poisoning is not known.

Runoff

Insecticide runoff occurs when chemical pesticides are sprayed onto eroding soil or when heavy rain falls right after an application. Insecticide runoff is dangerous to water supplies and local wildlife. A person who drinks water contaminated with insecticide from runoff can experience acute to chronic poisoning effects. Insecticide runoff can also negatively impact surrounding wildlife by killing or poisoning food supplies such as insects or plants. Excess runoff from insecticides may also kill fish.