In reply to chers: You need to ask yourself why you sweat? your body sweats to cool itself.
This could be fear sweat, Breath to cool down and regulate heart rate.
High blood pressure, same as above but consider diet also.
Physical activity makes you sweat. Climb at a steadier pace, drink more cold drinks and don't let your heart rate get too high, In turn train a little cardio so your heart gets used to pumping hard and keeping cool.
Damaged thin skin can also prove slippy particularly if your pulling hard on grit boulders all day. Look after your skin moisturize,soft thick skin is stronger than dry flaky skin and will take more of a beating. Ask any beauty therapist. Over use of chalk actually adds to skin damage. My chalk pretty much stays in my bag I find on a 10 hour day at stanage I'll probably need my chalk once, at which point I have to man up and live without, or ask my belayer to launch some at me.