I read the remarks about a guy who tried cinnamon oil diluted 20 to 1 with water and it still brought about an allergic reaction and he was very vocal in how bad the advice was that recommended it.
I used cinnamon oil full strength on my skin to check it for its ability to relieve mosquito bites and to repel them. It has given me no problems.
What I actually did was find that a very obnoxious mosquito had bitten me about six times very quickly all over my body while sitting at my computer and it was a small (and quiet) mosquito and didn't want to alight and stay in front of me so that I could murder him, so I grabbed my lavender oil and applied it and then, not getting relief as quickly as I wanted and wanting to check out the cinnamon oil's repellent properties, applied it to the bites and I was bitten no more and within 30 minutes (I didn't time it -- that's a guess) I felt the bites no more.
That's pretty consistent with lavender oil, though because there are different mosquitoes with different levels of irritation to their bites (and different levels of swelling), my experiences with applying lavender oil varies, although it is what I always use because I've found it reasonably effective in relieving mosquito and ant bites.
Two applications within a few minutes of each other practically always relieve the itch enough that it's no longer annoying within a reasonably short time span. No application can leave a bite itching for hours.