As far as essential oils go, i think it's better to do a more complex mix, some of the better ones are lemon eucalyptus, peppermint (use sparingly), lavender, lemon balm, and lemongrass–these are also some of the cheaper EO's if you shop around. Mix them in Karanja oil as the base. Mozzies and the like, can build up a tolerance to more simple or isolated chemicals faster, but i'm guessing a more complex mix might take a lot longer.
Lavender might affect hormones some, has estrogen like properties, but frankly, a number of guys here probably could use a little more of that… LOL. Well, in any case, health "authorities" recommend younger, pre pubescent and boys just starting to go through puberty to not use lavender. Hey, but weed lowers testosterone, and look at all the 6th, 7th, and 8th graders doing loads of that.
We could have a long talk about natural vs synthesized or super concentrated/distilled, but i doubt even the best arguments from both sides will change anybody's mind on it. For me, i lean to using things that are less concentrated/distilled, that are more synergistic, and less refined/processed–what some refer to as more natural–though more correctly called semi-natural. However, i'm well aware that even natural and semi-natural products can have high toxicity or cause adverse reactions. I've been experimenting on my body for awhile in this alternative and holistic health field, AFTER being experimented on by mainstream western medicine with no help but worse problems. So, not likely to change my mind on something that i have deep and repeated experience with. (Btw, i think western medicine is great for acute conditions).
Btw, i do not use EO's myself anymore for bug repellency. If i know they will be real bad, i wear thin, breathable long sleeve shirts and long pants, and over that put a mesh/bug net top and bottom. Also a very breathable, tilley type had with bug net. In Fairbanks (and other parts of) Alaska last early summmer, the mozzies were truly horrendous, i mean thick clouds and swarms. I have never seen anything like it in my life previously, not in the north east or the south east.
I wore a semi tight weaved linen shirt (still pretty breathable and cool), a breathable tilley type hat with bug net over same, shorts with bug net pants over same. Technically they could bite me through the bug net because i was wearing shorts, but the bug net pants were so baggy that they had a hard time even when i was still, and could not bite at all when i was moving. My get up did pretty well, and lot's of people seemed kind of envious.
However, if i wanted more full protection i could have worn some lighter, breathable linen or hemp-poly pants and then the bug net, and i would have been fine temp wise too.