What Causes Rectal Itchiness?

Hi i'm just curious. Sometimes my anus gets quite itchy and at times there is a tickling feeling. Not sure what the cause may be, I was thinking it may result from intestinal worms but this has been going on for a while and there have been no eggs or worms passed through my stools. I've heard sometimes coloured or dyed toilet paper can cause the itchiness please help me. Thank you