We have much in common, except for the severity of the GD outbreaks. Like you it was undiagnosed for years, dermatolgists assuming it was the Allergic Contact Dermatitis I had for voer 15 years. The cilantro put me into dormancy for over 2 years and in the last few months I have had a mild outbreak, same torso areas, but the itching and pain is tolerable. For 2 months have gone back on it as a daily routine and it seems my mild recurrance is simply stalled. My papuales are 5% in severity compared to past outbreaks. Yet why now after 2 years off.

Many say heat triggers GD, I do know heat makes it feel worse, but like you most my recurrances began in cooler dry weather, as Snowbirds spend our winter in Arizona. Ater the first outbreak of 1 full year the recurrances were every 6 months, then 6 months off, most beginning a few months after we got to dry AZ. I do believe friction triggers or in the very least severly aggravated my GD. We are off roaders, Jeeping and off roading in ATV's and that means the back in constantly pressed and rubbed against the seat. If I want to participate I must lean forward the entire time holding on to steering wheel or front hand bar if a passenger. Many seasons I had to give it up. I feel as if I am being dragged over a gravel road or rubbed with sandpaper, plus the papuales got more inflamed.

I've only been on a processed sugar free diet for 3 years now, this made a major change in my histamine levels and eliminated my internal stinging, zapping and burning which radiated all over inside my skin. Dairy free is a good idea, many in my family have this issue, so I simply try to keep it at a minimum but I do believe my pro-biotic, plain unsweetned yougut helps my gut. I do know if I've had too much dairy as I get gassy. Just a little is okay. Whey, even a small amount, will blow me up. Soybeans the same, yet I can tolerate other beans in moderation. The cilantro smoothie for me is no big deal. I didn't like how it made my yummy health smoothie taste bad, so now after removing the smoothie I put in my 1/2 bunch of cilantro, fresh or frozen, add about 1/3 cup of water and blend. Then chug. Easy.
Best of luck, you're trying to figure this out and keep at it.