Former Hey Dad! star Robert Hughes had boiling water thrown at him while in protective custody at Goulburn jail, an appeal hearing against his conviction has heard.

On Tuesday the Court of Criminal Appeal heard Hughes had been targeted by other inmates in prison despite being held in segregation in the maximum-security correctional centre.

Hughes is serving a non-parole period of six years, with a maximum term of 10 years, for 10 counts of sexual and indecent assault on four young girls in the 1980s and 1990s.