By the mid-1890s, baseball players began wearing gloves on the field, which inevitably gave rise to the practice of oiling their gloves. Ballplayers know the importance of a nice, conditioned glove. Rubbing on a little mineral oil once every season will soften and preserve the leather glove for years of continued use.
Mineral oil, or baby oil, is liquid petroleum, which is a by-product in the distillation of petroleum to produce gasoline and other petroleum based products from crude oil. The oil is colorless and composed mainly of alkanes and cyclic paraffins, and is related to petroleum jelly. Low in price and available in any drug store, mineral oil is a fine alternative to most manufacturer’s baseball glove oils or conditioners.
For many years, players used neatsfoot oil as a conditioner. Neatsfoot was the oil that came from boiling the leg bones of cows. Over time, however, neatsfoot oil can oxidize and tends to increase leather decay. Players began to experiment with other lubricants for their gloves, from shoe polish to baby oil, both of which are still common today.
According to the book “Glove Affairs: The Romance, History and Tradition of the Baseball Glove” by Noah Liberman, mineral oil keeps the pores of the leather open and in effect, keeps the leather "alive" while providing a softening condition. Mineral oil is useful as a protective waterproof coating for the leather. It is also an effective insect repellent, which is can be useful on a humid late summer evening, especially in the Midwest, when breeding gnats and mosquitoes tend to swarm ballfields.
A new glove should not be oiled to break it in. Oil is meant to protect the glove from drying out when not in use. When applying oil to the glove, be careful not to overdo it on the amount. Allow the oil to soak in and then rub it in, but don't leave it wet. Wet leather deteriorates faster.