Like many parents, I've never been convinced that chemical insect repellents are truly safe to use on my kid. DEET, in particular, creeps me out - once I accidentally sprayed some on a metal door, and the paint on the door immediately blistered up and peeled off.
DEET can irritate skin, but my primary concern was that it might bioaccumulate and cause neurotoxicity or cancer over time. I didn't know if there was any basis to my fears, so I spent several hours researching my concerns. This is what I found.
Summary: What Actually Works
The repellents proven most effective are DEET, Picaridin, or oil of lemon eucalyptus.
DEET and picaridin are most recommended by health organizations in areas where mosquito-borne illnesses occur
There's extensive evidence showing that they're safe for humans when used properly.
However, a majority of parents (including me) have doubted this.
The percentage of active ingredient in bug repellent doesn't measure its strength, but how long it's effective over time.
Lower percentage repellents don't repel bugs for as many hours as higher percentage repellents.
Lower percentage repellents need to be reapplied more often; products with less than 10% active ingredient offer 12 hours of protection (perfect for playing in the backyard after dinner, for example).
Consumer Reports says that "Repellents reach the maximum duration of effectiveness at 30%, so there's no reason to exceed that level."
Many repellents say they're EPA-Approved. This doesn't mean that the EPA says they're effective, only that they're safe to use.
Repellents do not protect all users equally and have varying effectiveness against different species of biting insect
Dealing with ticks is a bit different from dealing with flying insects; recommendations on ticks below.
Using a minimal amount of repellent based on the local environment and reapplying as needed is the safest bet.
Lotions last longer than sprays.
Sprays can be applied to clothing, where they're effective longer than on skin.
Where insect-borne disease such as malaria, West Nile virus, or Eastern Equine Encephalitis is common, the danger from those serious illnesses is vastly greater than getting sick from insect repellents.
What I Do For My Kid & Why
Since insect-borne disease isn't common where I live, DEET-free Cutter Eucalyptus Insect Repellent spray is what I usually use on my kid.
It's the highest-rated natural insect repellent on Amazon.com. It's based on oil of lemon eucalyptus, which is the most effective "natural" repellent - as effective as 7 - 10% concentrations of DEET. This means it has to be reapplied every 2 hours or so.
The CDC has recommended oil of lemon eucalyptus for children older than 3 in regions without malaria or West Nile virus. However, it isn't super effective against sand flies or no-see-ums.
If my kid is away from the family and outside all day (for example, at day camp), I use Fisherman's Formula Sawyer Picaridin, which was recently top-rated by Consumer Reports. I only use it on her exposed skin.
I've also had good luck with Natrapel picaridin wipes.
Picaridin is registered in over 40 countries worldwide and has been shown to be as effective as DEET, but without the smell, oily residue, or potential irritation to skin and eyes. Unlike DEET, picaridin won't warp, melt, or discolor plastics and synthetic clothing or camping gear.
The World Health Organization recommends picaridin for malaria prophylaxis, saying it demonstrates excellent repellent properties comparable to, and often superior to, those of the standard DEET.
Picaridin is a synthetic compound based on compounds from black pepper plants. It was developed in the 1980's, is widely in Europe and Australia, and became available in the US in 2005. It's rated as the longest lasting repellent with up to 14 hours of protection.
It works against mosquitoes and variety of flies, chiggers, and gnats. While manufacturers claim it's effective against ticks, I haven't found any third-party study that confirms this. (Indeed, even DEET seems to have a minimal effect against ticks.)
Here's what you need to know about repelling ticks:
There are several types of ticks that spread several types of disease.
Only deer ticks transmit Lyme disease.
You have 24 hours to find and remove most ticks before they transmit disease.
Always check yourself and your kids thoroughly after outdoor adventures. Fair warning: ticks love to crawl up into warm, hidden places.
In infested areas, tucking your pants into your socks is dorky but highly effective for keeping ticks from biting.
Wearing smoother, light-colored tightly woven fabrics makes it easier to spot ticks vs densely woven fabrics like wool.
DEET and Picaridin are fairly poor tick repellents.
CDC recommends using products with 20% DEET on exposed skin to reduce biting by ticks.
The most effective commonly available tick repellent is permethrin.
Permethrin must be sprayed on clothes. Never spray it directly on skin.
Allow 24-48 hours for clothes treated with permethrin to dry after spraying.
In infested ears, shoes, shorts, and pants treated with permethrin, and socks treated from the ankles up are recommended, along with DEET on skin.
Commercially-treated permethrin-coated clothes can last up to 70 wash cycles and are recommended for heavily tick-infested areas.
IS DEET SAFE?
When applied as directed, DEET is considered safe by most public health organizations. But concerns endure. In Vermont I choose not to use it. I would use it if I was traveling in an area infested with malaria or other insect borne diseases. The danger of those diseases is greater than the risk from normal use of DEET.
Consumer Reports writes that DEET in high concentrations can cause rashes and disorientation.
Rare allergic, or toxic reactions have been reported for people with chemical sensitivity.
Nearly all of the DEET that is taken in through the skin is eliminated by the body within 24 hours of applying it.
Disconcertingly, DEET can warp or discolor some plastics and synthetic fabrics.