legally they are data protected. Especially as a beauty therapist you have hold of possibly someones name ,address, date of birth , What medication they may be on,what operations they have had, what job they do, how many children, ive even had cards to fill in before in previous jobs that have asked people ''are you constipated''.
They should be locked away. Ideally the actual info should be only numbered ie client 1 etc and the corresponding name address etc kept separately.If the info were to ever go missing you are responsible.
Keep questions and info on cards to the least you need to know for the treatment.