A galactocele is a cystic tumor containing milk or a milky substance that is usually located in the mammary glands. It is caused by a protein plug that blocks off the outlet. Galactoceles are benign and are not a cause for concern. Once lactation has ended the cyst will resolve on its own without intervention. A galactocele does not cause infection as the milk within is sterile and has no outlet for which to become contaminated. Attempts to drain the cyst are unsuccessful because the protein plug remains intact and milk production continues.