As a full contact martial artist, I took a class in which an instructor who's pretty famous and knows his stuff called a guy up to help him demo. The guy stood up and walked maybe three steps when the instructor smacked him hard in the face.
The instructor then apologized, and said he's making a point. He asked the man if his hands and his temples were sweaty. It had been maybe 10 seconds, but sure enough both areas were completely damp.
The instructor then pointed out that under stress, our temples and palms tend to sweat as part of our ingrained fight or flight response, like hair standing up.
If you're nervous when you perform, sweaty palms are the symptom. Calm your nerves, thus treating the cause, and your symptom will subside.
Pj