This information was passed along to me many years ago. It has worked for me although I could not tell you why. I have my ideas but no real scientific data to rest my claim on.
In the trout environs of Southern California you can always count on this fact as a constant, mosquitos abound! For years, I would purchase a new bottle, jar, tube spray of the latest and greatest DEET insect repellant for the summer forays into the wild. Usually, the products worked but required numerous applications during the day, was a stinky sticky mess and should you get it wet it was gone and a new application required.
Then my mystery friend informed me of his method and a summer ritual was born.
A minimum of 10 days prior to an outing where you expect mosquitos you start taking two different vitamin supplements, a Vitamin B Complex and a Garlic capsule. There it is!!! The secret of no more bites.
The theory is that both of these supplements eventually leech from your skin and produce a very effective bug repellant film. Try it you will be surprised and both of these supplements are not something dangerous to your health and can be stopped without recourse.
Your fishing buddies will be amazed when you just head for the water while they are next to the truck slopping on the goo.