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The  use of insect repellents is strongly recommended by the Centers of Disease Control and Prevention (CDC) and the Environmental Protection Agency (EPA) to prevent infectious diseases transmitted by mosquitoes and ticks. Insect repellents applied to exposed skin or clothing should be used together with long pants and shirt sleeves, plus avoidance of outdoor activities during peak mosquito-biting times. Mosquitoes can transmit Zika, chikungunya, dengue, West Nile, Eastern equine encephalitis, yellow fever, and malaria. Ticks can transmit Lyme disease, rickettsial diseases such as Rocky Mountain spotted fever, and viruses such as Powassan virus.

One of the most effective insect repellents is N,N-diethyl-m-toluamide (DEET). It is highly effective against both mosquitoes and ticks. It is available in concentrations from 5 to 99 percent; higher concentrations provide longer-lasting protection, however concentrations above 50 percent do not improve efficacy. Reviews of DEET indicate that it is generally safe to use. Toxic and allergic reactions are uncommon, although it may feel oily or sticky on the skin and may damage some synthetic fibers and plastics. It may be used on children in concentrations up to 30 percent and on infants over two months old. It may be found in products by Cutter, Off!, Sawyer, Ultrathon, and Repel 100.

Picaridin provides protection against mosquitoes, ticks, flies, fleas, and chiggers. It is available in concentrations between 5 and 20 percent and is safe for children in concentrations up to 10 percent. It is as effective as DEET. While it may cause eye and skin irritation, it is not oily, and is colorless and odorless. It will not damage clothing or plastics, but may stain leather and vinyl. It is available in products by Cutter, Avon Skin So Soft, Natrapel, and Sawyer. IR3535 is a synthetic version of the amino acid alanine. It is available in concentrations of 7.5 and 20 percent. It repels mosquitoes, flies, and deer ticks. Several studies found the 7.5 percent concentration to be ineffective. It may cause eye irritation and may damage clothing and plastics. It is safe on children over 2 months old. It is available in products by Avon Skin So Soft and Coleman.

Oil of lemon eucalyptus (OLE) occurs naturally in the lemon eucalyptus plant and is synthesized for commercial use as a repellant. It repels mosquitoes, gnats, ticks, flies, and biting midges. Lab studies have found it as effective as DEET for mosquitoes. It may cause eye and skin irritation and may trigger allergic reactions (citrus allergies). It is not recommended for use in children under three. It can be found in products by Off!, Coleman, and Repel. A relatively new repellent is 2-undecanone and is derived from the wild tomato plant. It is available in a 7.75 percent spray formulation called HOMS Bite Blocker. It can have a strong odor. Less effective repellents are essential oils obtained from botanical materials and citronella oil-based repellents. Both may cause skin irritation and must be re-applied frequently. Lastly, a synthetic repellent called permethrin may be applied to clothing and is highly effective against ticks. It remains active for several weeks. One final point—avoid using products that combine a repellent and a sunscreen because the ingredients have different re-application intervals. If using both products separately, apply the sunscreen first. Putting sunscreen over insect repellent renders the repellent ineffective.

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