A recent NEJM showed that Insect repellants containing the chemical DEET are more effective mosquito deterrents than other synthetic repellents or plant-derived products.

DEET (N,N-diethyl-3-methylbenzamide) is a chemical that was patented by the US Army in 1946 and is still recognized as the most effective mosquito repellent available. However, many consumers may balk at applying DEET to their skin and instead try plant-based products or other alternatives.

The researchers pitted several DEET-based insect repellents against seven botanical products and another synthetic repellent containing a compound called IR3535. The researchers also tested three wristbands containing either DEET or citronella, a plant oil common in botanical insect repellents.

They found that, overall, DEET products offered longer-lasting mosquito protection to the 15 volunteers tested. A formulation with 23.8% DEET provided just over 300 minutes of complete protection, according to the report. That compared with about 23 minutes with the IR3535 product, and an average of less than 20 minutes for most botanicals, which were largely citronella-based. None of the wristbands were effective.

One plant product was, however, comparable to the lowest-concentration DEET product. This soybean-oil-based repellent provided about 95 minutes of complete protection, on average, the investigators found.

While another plant product, that uses a mixture of herbal ingredients excel well after being left in the well ventilated room for 3 days and more. The protection last for 10 - 20 days in the room.

In addition, Fradin and Day tested a eucalyptus-oil product that was introduced in the US after their study was completed. Among six volunteers, the product provided an average of 2 hours of mosquito protection.

The New England Journal of Medicine July 4, 2002;347:2-3, 13-18