As a living mosquito magnet (you have no idea, it's ridiculous), the thought of having to re-douse myself every 30-45 minutes with an insect repellent is, well, repellent. And 30-45 minutes is just about the length of time that most natural or homemade insect repellents will last. If that's all the time you need a repellant to be effective, then vanilla extract (or most any essential oils or natural oil product, like citronella oil) is a good choice.
Synthetic repellents tend to be more effective and/or longer lasting than "natural" repellents. Consumer Reports, as well as numerous other studies, show unquestionably that repellents containing DEET, picaridin, or IR3535 are more effective than repellents with "natural" active ingredients. A 2006 study published in the Journal of the American Mosquito Control Association, and affirmed by the CDC, show that oil of lemon eucalyptus in a 40% concentration is equally effective as DEET, picardin and IR3535.
The CDC also affirmed what many with home organic gardeners have know for years, neem oil makes a terrific mosquito repellent for up to 12 hours. It's cheap at Walmart and other gardening centers. Comes in a concentrate jug or in a spray bottle.
Need oil is a vegetable oil pressed from the fruits and seeds of the neem tree, an evergreen which is native to India. It is used in cosmetics, mainly hand creams, hair care products and soaps. It is used medically to treat skin inflammations and things like eczema. But it's in organic farming that it shines brightest, as it repels a wide variety of pests including the mealy bug, aphids, the cabbage worm, whiteflies, mites, fungus gnats, beetles, moth larvae, mushroom flies, leafminers, caterpillars, locust, nematodes and the Japanese beetle. At the same time it's harmless to mammals, birds, earthworms and some beneficial insects such as butterflies, honeybees and ladybugs, as long as it's not highly concentrated directly into their area of habitat or on their food source. It can be used as a household pesticide for ants, bedbugs, roaches, flies, snails, termites and, most importantly for me, mosquitoes. It works as a repellent, insecticide and larvicide. Neem oil is also an effective fungicide and controls black spot, powdery mildew, and rust (the bane of soybean farmers).
Of the commercial insect repellents that made the grade with Consumer Reports and the CDC for both ticks and mosquitoes, the ones that rated highest in effectiveness and longevity, lasting 8 hours or more, are:
Off Deep Woods Sportsmen II (deet 30%)
Cutter Backwoods Unscented (deet 23%)
Off Family Care Smooth and Dry (deet 15%)
3M Ultrathon Insect Repellent 8 (deet 25%)
Natrapel 8-Hour with picaridin (picaridin 20%)
Bite Blocker Extreme was almost as effective, containing oil of lemon eucalyptus, but didn't work as long on
Aedes (dengue fever, yellow fever) or Anopheles (malaria) mosquitoes as it did on Culex (West Nile, encephalitis) mosquitoes.
Trust me, I can ID all them at a glance.
At the house we have a lot of ivy and a wooded area next to the driveway, and mosquitoes go nuts in there. At dusk there will be mosquitoes all over me while ignoring most anyone else I'm out there with. Ticks me off, pardon the pun. So it's Off, Cutter or Neem Oil for me. I highly recommend any of them. We have all three at the house, so whichever one I grab first gets used. I usually carry a bottle of one or the other in the van, usually Off. I prefer neem oil because it's hydrophobic and won't wash or sweat off, but it usually has a strong odor, kind of like a mixture of peanuts and garlic. It's not a pleasant odor at all, and it tastes really awful (so don't try and cook with it even though it's a natural vegetable oil).
A couple of times now I've parked for a short nap, with a cracked window without having put in the window screen, and I've awaken to being bitten relentlessly by mosquitoes. Once in Louisiana I parked in a great spot for shade, not realizing that a few feet into the wooded area was a swamp where mosquitoes were breeding like, well, mosquitoes. I woke up in the middle of the night with fur made of mosquitoes. Freaked me out. And they weren't all that particular about where they bit me, either. That night almost caused me to stop sleeping nekkid, or at least start wearing shorts or something. Go ahead, laugh, get it out of your system. Karma will get you back.
Here's a
Web page that shows the difference between the three mosquitoes you are likely to encounter.
Here's a
Snopes page about Bounce Fabric Softener Sheets, B1 vitamin pills, bananas, Skin-So-Soft Bath Oil, Vick's VapoRub, marigolds, Lemon Joy and frogs. 
