1.
If something eats into your time or your resources, it uses them, when they should be used for other things.
Responsibilities at home and work eat into his time...
PHRASAL VERB : V P n
2.
If a substance such as acid or rust eats into something, it destroys or damages its surface.
Ulcers occur when the stomach’s natural acids eat into the lining of the stomach.
PHRASAL VERB : V P n