A hairstylist is a member of the make-up department who specifically concentrates on the coifs of the actors. They are usually a kind of "continuity supervisor for hair", as well, refreshing and amending the actors' hairstyles throughout a shoot.
As it is typically more of a North American title, this credit has only been used for the 1996 tele-film. Julie McHaffie therefore has the distinction of being the only credited hairstylist in Doctor Who — though not Doctor Who universe — history. In most fully British productions, hairstyling is considered part of the function of the make-up artist.