Ah! That would depend on how hot you set the dryer. I use mine on low heat, and haven't noticed any bad effects on my hair. As long as you don't use high heat, you should be fine.
You can also let your hair air dry when set on rollers, which is what many women did back when roller sets were the norm. It is possible to sleep with them in, but I don't recommend it if you want a good night's sleep.
Baby Fine 3B, low porosity, normal density and elasticity
CGing since July 2008