Ants follow each other or an invisible scent trail to a food source, both inside and outside. Lemon juice can deter the ants from entering a home by masking their trail into the home.
Lemon juice does not kill ants, but its smell and acid disrupts the scent trails they leave for other ants. The next group of ants will not be able to follow any paths, and the citrus smell will discourage them from starting a new one.
Pour a few drops of lemon juice into the hole or crack the ants are using to enter or leave. You can also soak a paper towel in lemon juice and wipe around the point of entry.
Lemon juice is a natural product and will not harm humans or adults who come in contact with it. Lemon juice fresh squeezed from lemon works, as does artificial lemon juice bought at a grocery store.
Soak paper towels in lemon juice and wipe down the inside and outside of door frames and window frames. This may need to be repeated often to prevent the ants from entering your home.