Have you ever wondered what actually causes holes in Swiss cheese? A group of Switzerland-based scientists have found the answer.Scientists from the Switzerland-based Agroscope Institute for Food Sciences have determined that microscopic particles of "hay dust" were getting trapped in the cheese, according to ABC News . The trapped particles allowed the distinctive holes to form in the cheese from trapped carbon dioxide gas.The mystery behind Swiss cheese and its peculiar holes dates back to 1917, when an American scientist originally theorized that the holes were caused by bacteria. But it was only until an article published in the International Dairy Journal found out the whole answer to the Swiss cheese dilemma."After spending several years on that topic, the discovery of the magic effect of traces of hay dust on eye formation was for the whole team somehow just an enlightenment," Daniel Wechsler, an author on the study, told ABC News in an email. "The solution is so simple, it's almost incredible that this mystery remained unsolved until nowadays."Wechsler and his fellow researchers believe tiny capillary structures in the hay dust can start the formation of holes in the cheese. After making the discovery, Wechsler told ABC News he felt like celebrating. "It feels just like 'Say cheeeeeeeeeeeeeeeeeeeeeeeeeese.'"