What cause an cut in the labia of the vagina.

It could: Be due to intercourse, vaginal dryness, it may feel sharp like a cut but not actually a skin lesion present. It's likely irritation due to intercourse and without adequate lubrication.

Options: An open sore on the labia may be anything from irritation from a yeast infection to herpes. It my be dryness. Sometimes a new, larger partner will cause the tissue to tear. She should see a gyn.

Many things: Trauma to the area, having intercourse without enough lubrication, certain infections. See your gyn for an exam to be sure of the right diagnosis and treatment.