Is a capacitive touch screen safe to use?
Since there is an insulating layer on top of the conductive layer (making one side of the capacitor), there is no real current flowing from the screen to your finger.
When you put your finger on the screen, you are adding the missing plate of the capacitor, thus completing the screen capacitor. The current flowing through your finger is not really coming from the screen.

Numbers

Capacitor values are about 1 pF - 1 fF, and the voltage switch is in the range 10-100V (usually 12, 24 or 48V) in micro seconds ~ 1 MHz signal. So, using the below formula for capacitor:

\$ i = C \frac{dV}{dt}\$

we have a max transient current of

\$ i = 1.10^{-12} . \frac{100}{1.10^{-6}}\$ = 100 uA

100 uA is safe for your body.