There are two seals in place when the product is manufactured. One seal is a tamper band connected to the cap that separates upon opening the bottle, the other is a vacuum seal that is created during pasteurization. In rare instances, this vacuum seal may be broken. This may typically occur when a bottle experiences high impact due to rough handling through distribution. Air may potentially get into the bottle and mold may then be able to develop. As with any natural product without preservatives, such as bread and fruit, contact with outside air can cause a common mold to form. This is not something that would cause any health issues.