Patent law states "On taking up an application for examination or a patent in a reexamination proceeding, the examiner shall make a thorough study thereof and shall make a thorough investigation of the available prior art relating to the subject matter of the claimed invention." This means that prior art could disqualify your application for a patent.
According to Patentcafe prior art is "the total body of knowledge, which teaches or otherwise relates directly to an invention. This is the primary criteria in determining the patentability of a new invention. Establishes novelty and unobviousness of the art that relates to the invention in question. Prior art references include documentary sources such as patents and publications from anywhere in the world, and nondocumentary sources such as things known or used publicly."