Not around the waist, exactly, but there may be something to that. (whitefonted for possible TMI)
It's mostly been armpits and places that are either under or close to the elastic bits of my (always breathable cotton) underwear--hips, inner thigh, etc. In the summer I was also getting it on my stomach and under and around my breasts, especially around where the edge of my bra hits.
Oh, and I always use unscented laundry detergents and never use dryer sheets, so that rules out some of the more obvious allergies for this pattern of a rash.
I ask because a rash associated with sweating is often related to being allergic to your laundry detergent. You might want to try Tide Free. I can't use anything else, and I used to recommend it in karate and it seemed to clear up rashes for a number of people. (You think people in karate classes are talking about serious martial arts philosphy? No, they're talking about how they wash their gis and what hurts.)
eta: Susan edited to make my post sound crazy. Is there something else that could be reacting with sweat, such as soap or lotion?
It sounds like it could be fungal to me, Susan. Have you had your blood sugar checked, recently? Do you consume a lot of sugar, and/or flour?
Is there any reason Tide Free would be better than All Free & Clear? Because the latter is what comes in giant vats at my local Costco.
Blood sugar is fine, right in the middle of the normal range. At least, it was six months ago, and I already had this stuff then. And my NP thought it was fungal, and treated it accordingly, which made it better but didn't cure it completely. The dermatologist is less sure, but that's why I have to leave it untreated and go back Monday. Grr. Itch itch itch.
I do love the carbs, and dammit, no one is taking my bread from me! If this is fungal, there should be a drug that kills it.
Susan, I'd try the Tide, as it might be some random chemical (ie not a fragrance). Body chemistry is a strange thing.
Tide Free has been better for me, although All is okay. As DebetEsse says, you could just use one box of the Tide and see if it helps.
Soap can be really tricky too. A surprising number of people are allergic to Ivory, for example. I stick with Dr. Bronner's.
Susan, it really sounds fungal. I only say that because I've had the same thing, and the only thing that made it go away for good? Tea Tree oil.
I've got tea tree oil in the medicine cabinet--I've used it on zits in the past. Which just gives me one other thing to be tempted to use now and not wait till Monday, because this shit ITCHES.
would using the tea tree oil be at cross purposes with your doctor's visit? I'd use it, and then tell the doctor that you did, and what the results were. It may help her to rule stuff out, even.