I got 4 identical opaque white plastic containers, and labeled them on the bottom, one as the allergen and the other 3 as placebo. I started out testing myself with just 5 mg of corn starch, in a water solution. That small an amount doesn't show up in the water solution, so I used containers with just plain water as the placebo in the beginning.
I randomized the vials in a microwave for a 3 minutes and an arbitrary number of seconds, on the lowest power so they wouldn't get hot. I went away while the microwave was running. Then I took the vials out of the microwave one by one with my eyes closed, and put them in the fridge.
I consumed the vials one by one on different days, being careful to keep the bottom out of view as I poured the contents into some food. I also did my best not to look at the contents of the vials as I poured them out. I put a tag with which day it was inside the vial, closed the top, and put it into a box, being careful to shield the bottom of it from view. Then I noted down my reactions in a log file. At the end of the 4 vials, I wrote down my guess as to which day I'd gotten the allergen, and I compared my guess with which day I'd actually gotten it.
If I felt OK on a day when I'd gotten a dose of the corn starch, I knew I wasn't sensitive to that dose.
But if I was sick on a day when I didn't get a dose of corn starch, it didn't tell me anything, because I could have been having an allergic reaction to something else, like mold in the air.
I found I felt OK on one day when I turned out to have consumed the vial with 5 mg of corn starch.
Before doing the blind trials, I'd been trying to desensitize myself by consuming 5 mg of corn starch per day, and I'd felt a slight reaction. But after I felt OK when I'd consumed 5 mg of corn starch blind, I knew the slight reaction I'd had was a nocebo effect. I was consuming the corn starch at the same time every day, and it seems I got used to feeling the reaction at that time of day.
So then I tried 10 mg of corn starch vs. placebo. I had to use arrowroot starch as the placebo, because I found I could see 10 mg in the water solution.
I felt OK on one day when I turned out to have consumed 10 mg of corn starch, so I knew 10 mg of corn starch doesn't noticeably affect me.
So then I tried 20 mg vs. placebo. I felt somewhat sick on the day I got the corn starch.
So I tried again with 25 mg. This time, I got rather sick when I ate the corn starch, for about a day; and I felt no worse than usual when I ate the arrowroot starch. This happened with my 4 vials, 3 times in a row - so there would be only a 1/64 chance of having that result by accident.
So it's definitely a real allergy, not just a nocebo effect. According to the USDA nutrients database, corn starch has 0.26% protein. So I'm sensitive to about 50 mcg of corn protein.
Knowing my actual sensitivity to corn protein has already been helpful to me. I avoided iodized salt for a long time, because it contains dextrose, which is made from corn in the USA. But I was able to calculate about how much corn protein I'd be getting per day from iodized salt, and it's far less than the amount I'm sensitive to. So I can use it as a source of iodine.