If something as seemingly benign as sunlight can harm your skin, it's not hard to imagine that insect repellents might do the same. In fact, insect repellents can cause skin rashes and irritation. For instance, one study found nearly half of the people using a highly concentrated formula of DEET on the sensitive inner elbow reported adverse effects [source: ASTDR]. The good news is that if one repellent reacts badly with your skin, you probably can find another one that doesn't. Let's look at some of the most popular insect repellents to learn what they're made of and how they affect your skin.
DEET. By far the most popular repellent sold in the United States, DEET was used by more than 200 million people worldwide in 2008 [source: ASTDR]. It's perhaps the most effective repellent on the market, particularly when used in high concentrations. Unfortunately, frequent use of repellents containing a high percentage of DEET can cause a number of adverse reactions, including blisters, rashes and even scarring. Even so, negative reactions to DEET are rare considering the number of people who use the repellent, and washing your skin after returning indoors can help further reduce irritation from exposure.
IR3535. IR3535 is a synthetic repellent available in concentrations of up to 20 percent. The repellent has proven to be nontoxic, causing no skin irritation to speak of. While IR3535 has a great safety record, its effectiveness can't match DEET's. According to one study, IR3535 was found to be only one-eighth to one-hundredth as effective as a similarly concentrated DEET repellent [source: Fradin].
Picaridin. Derived from pepper, picaridin is widely available in Europe and Australia, but is only available in lower concentrations in the United States, barring further study. The repellent appears to be completely safe for the skin, though it can still cause irritation if it touches the eyes. Best of all, one study found picaridin to last 70 percent as long as DEET, making it a highly effective alternative [source: MSDH].
Oil of lemon eucalyptus. Derived from a particular species of eucalyptus tree, oil of lemon eucalyptus is one of only three repellents registered with the U.S. Environmental Protection Agency. Research has shown oil of lemon eucalyptus, often referred to as PMD, to be the most effective of all plant-based repellents. Studies have shown PMD to cause eye irritation but little else, though individuals have reported occasional skin irritation after using a PMD-based repellent.
Overall, insect repellents are safe and effective, providing more good than harm for users. By following the instructions provided on repellents' labels, you put yourself and your skin at very little risk using any insect repellents currently on the market.