UPDATE 2011-07-08: Based on additional research I've done into the long term use of topical corticosteroids, I have stopped using it to treat my irritation problem. Instead, I've decided to pickup a few extra Hydryx Workout Towels in order to soak up the sweat before it gets a chance to cause problems.
Every time sweat or perspiration appears on my forehead, it is followed within minutes by a fairly uncomfortable burning sensation. Nothing dibilitating or severe, but incredibly consistent:
Engage in sweat-inducing level of physical activity -> start sweating -> burning sensation on forehead and temples.
The burning sensation persists for the duration of the activity, and about 30 minutes afterward. To make matters worse, these episodes often lead to the appearance of acne in the same areas by the next morning. Because of this, I often avoid strenously aerobic gym routines or any activity that starts me sweating.
Only recently did it occur to me that I may not be the only person on the planet to suffer from this condition. Sure enough, a few Google searches turned up quite a few reports of similar symptoms. Duh. A few of those posts indicated that it could be an (auto-immune?) inflammation reaction - either induced by the sweat liquid or the heat that accompanies it.
So the next morning I grabbed a tube of cortisol/hydrocortisone (generic "1% Anti-itch cream") from the medicine cabinet and smeared a small amount on my forehead and temples before heading to the gym. I made sure that the workout included some high-intensity invterval training, which will always get the sweat flowing.
Sure enough - there was no burning. No irritation. No acne eruption the next morning. I've been using this regimen for about a week now, and have not experienced the burning or irriation in that time. Problem solved? I sure hope so. I'll follow up in a few weeks if the treatment is still working.