Probably won't hurt them. I've used both olive oil and lemon oil. But I agree with most everyone else -- buy a new set.
At this point you really need to change your strings.
It wont wreck them, it will *** your sound up... use tongue oil on frett board or virgin olive oil. There is a product called fast fret, that is a miracle worker on string life... elixer strings have a nanoweb technology that has triple the sound life to any other brand on the market... that's all I got...
Just pluck down (no pun intended) $6 and get a new, shiny set.
you can boil the wound ones to remove oils built up and just pull the plain ones through a rag with wd40 to clean them ,,then apply them ,,and wipe them with a silicone ba<x>sed product called squeak ease or its equivalent ,and you can get some life back in a dead string and don't let them boil to long either ,,,,but nothing beats the sound of new strings if you want a clean sound ,,,some pla<x>yers never change them until they break because they like the dead sound ,,,,but I have used the way I just told you and it worked ,,,,not my invention either an old rocker told me ,,,,hope this was useful