Using insect repellant is important in Colorado due to the occurrence of West Nile Virus carrying mosquitos in the region. I like to not use products that contain DEET for the following reason. I use Bite Blocker instead as it seems to work the best in my personal experience.
DUKE UNIVERSITY REPORT ON DEET
Every year, approximately one-third of the U.S. population uses insect repellents containing DEET to ward off mosquitoes and other pests. At present, DEET is used in more than 230 products with concentrations up to 100 percent.
However, DEET should be used with caution due to its possible damaging effects on brain cells. Studies have shown that DEET causes brain cell death and behavioral changes in rats after frequent and prolonged use. This exposure causes neurons to die in regions of the brain that control muscle movement, learning, memory, and concentration. Rats treated with an average human dose of DEET (40 mg/kg body weight) performed far worse when challenged with physical tasks requiring muscle control, strength and coordination. These findings are consistent with reported human symptoms following DEET's use by the military in the Persian Gulf War.
With heavy exposure to DEET and other insecticides, humans may experience memory loss, headache, weakness, fatigue, muscle and joint pain, tremors and shortness of breath. These symptoms may not be evident until months or even years after exposure. The most severe damage occurs when DEET is used concurrently with other insecticides, such as permethrin, for prolonged and frequent periods of time.
At this time, there is little information about the short-term, singular and occasional use of DEET. Further government testing of the chemical's safety is necessary. However, frequent and long-term use of DEET, especially in combination with other chemicals or medications, could cause brain deficits in vulnerable populations, particularly children.
Until further studies are done, it is important to be cautious when using this insecticide:
Use insecticides containing DEET sparingly and infrequently. If you do use one on your skin, avoid wearing it for prolonged periods of time.
Be wary of using insect repellant containing DEET on children. Children are more susceptible to subtle brain changes caused by chemicals in their environment because their skin more readily absorbs them. Also, their still-developing nervous systems are more potently affected. For the same reasons,
NEVER use insect repellant containing DEET on infants.
Be aware that DEET can be present in commonly used preparations like insecticide-based lice-killing shampoos. Use the same precautions with such preparations as you would with insect repellant.
Do not combine insecticides with each other or use them while using other medications. Even an over-the-counter antihistamine could interact with DEET to cause toxic side effects.
Do not spray your yard for insects and then take medications afterward. There is a possibility that you've inhaled a small amount of the insecticide that might interact negatively with the medication. Also, be sure to wash your skin thoroughly after spraying your yard. Lawn treatment chemicals are very strong and were not formulated to be applied to human skin.