Correct spelling


Correct spelling, explanation: itself is a reflexive pronoun, from Old English hit sylf, thus it + self. Although from the 17th century it is used rather in the meaning of its own self, the origins point to itself, not itsself.

Definition of itself:
pronoun, the reflexive pronoun for 3rd person singular it
These actions could be threatening to the industry itself.
The soup itself was really tasty but the rest of the dinner wasn’t very good.

Incorrect spelling


Incorrect spelling, explanation: doubling the s consonant in itself is wrong, so itsself is an incorrect form. This is due to the fact, that the word originally was created from it and self, not its and self. Therefore itsself is the correct spelling.