Hi all, while researching, I stumbled across this method to DIY allergy/intolerance test founded by Arthur F. Coca, M.D in about 1950 or so. It's called The Pulse Test. He wrote a book about it in 1956 after his wife suffered from many illnesses/vague symptoms but didn't know what they were.
Anyhow, to cut to the chase and to summarize what the test is about, you check your pulse before and 30 minutes after eating a single food. If it goes up significantly (over 15) you may have a problem with that particular food and avoidance tests should be done to see if it's causing your symptoms.
This actually makes sense, since if you have a fever, it's your body's immune system going into overdrive to kill what is causing your illness. During a fever, your pulse will skyrocket (I think +10 bpm per degree raise of body temp) The same thing would happen if your immune system is activated by a food that you have recently eaten. It may not work however for those foods which give a delayed response (in my case, a lot of them don't show up until 48 hours later).
I personally haven't tried this, but the book is still in print 60 years later, is a totally free, easy and DIY way to see if you have food intolerances if it works. For people that can't afford a lab-assisted test, this could really help them pinpoint if foods are causing their illness (rosacea).
Just thought I'd throw this out there.