Civil Code § 45a

A libel which is defamatory of the plaintiff without the necessity of explanatory matter, such as an inducement, innuendo or other extrinsic fact, is said to be a libel on its face. Defamatory language not libelous on its face is not actionable unless the plaintiff alleges and proves that he has suffered special damage as a proximate result thereof. Special damage is defined in Section 48a of this code.