Buy a terry cloth hat. Saturate it with cold water and wear it until it starts to warm up. Wet it again, wear it...repeat as needed. This has worked for me even in conditions of relatively high humidity. I don't know about jungle weather (near 100%).
Alice, are you able to garden early in the day? The hotter temps usually force me to garden early and again in the evening. Of course, I spray anything with Deet on my skin because the mosquitoes are out then.
Don't know your age or fitness level, but for me (I turn 60 this summer) gardening daily is the key because then I'm in better shape. Our bodies also seem to acclimate better to the heat that way. I confess that I take frequent breaks to stay well hydrated and just to get out of the heat. Of course, then I get waylaid by the computer. Sigh.
Like you, Alice, I prefer to not to wear a hat, although my skin would be better if I did. I need the cooling effect of any breezes!
I do try and most of the garden work in the cooler hours of the day, but more often then not there's just too much work that needs to be done. I have a lot of roses that need constant spraying, watering, spraying, feeding and more spraying.
And since we've had almost no rain at all this spring, everything needs watering!
What I've been trying the past few days seems to be helping. I use hand towels or cut up old towels, dampened and put in the freezer until frozen. Then I wrap them around my neck...really cools you off quickly. Not very attractive but my plants don't seem to mind.
I know it's around my head, but I wear a rolled-up bandana as a sweat band. Take a 10-minute break every hour and rinse it with water (from the faucet) and wipe your head down to cool down. Have a lawn chair in the shade to just sit and admire your handiwork!
But the key for me is not to work in the heat of the day. Otherwise it wouldn't be playing! That's where the rules come in - you have to try to do a little bit every day, and I do it early in the morning and after about 6:30 in the evenings, usually staying outside until I can't see anymore. With the birds chirping and all, it's just a wonderful way to garden. And maybe you have a wee bit too much garden? Cut back a little, so it's managable in mornings and evenings. (I know, I know, that's almost impossible. At least commit to not building any new beds or buying any new plants except to replace what you might be taking out.)
Too much garden? Never! I don't think it's a matter of too much work. I do have small periods of time that take me away from my gardens so I'm often having to play catch-up...but this is really only an issue in the spring when there's so much to do. And in a month or so there isn't really a cooler part of the day, just hot and hotter. I've spent this spring installing drip lines and soaker hoses in all the beds to save me from moving sprinklers around all day during those really hot summer months.
Thanks for the suggestions.