Major League Baseball has slightly deadened its baseballs amid a home run surge over recent years, according to a source.

MLB anticipates the changes will be subtle and a memo to teams cites an independent lab that found the new balls will fly 1 to 2 feet shorter on balls hit over 375 feet.

Five more teams also plan to add humidors to their stadiums, meaning 10 of MLB's 30 stadiums are expected to be equipped with humidity-controlled storage spaces.