The SPF (sun protection factor) number on the package label refers only to UVB protection. An SPF of 30 absorbs 95 percent of the sun's UVB rays; higher numbers confer a modest additional amount of protection, so that an SPF of 50 absorbs 98 percent of the rays.
Some people still fear DEET because of 14 potentially DEET- related seizures over a period of 40 years. But both the federal Centers for Disease Control and Prevention and the American Academy of Pediatrics now say that DEET can be used safely by adults and children over 2 months old.
In April, the CDC announced that two new repellent ingredients - picaridin and oil of lemon eucalyptus - are comparable to DEET at certain concentrations. But it's less clear whether the two new ingredients are as effective as DEET against ticks, [Michael Shannon] warned.