Praise be to Allah.
It says in Fataawa al-Lajnah al-Daa’imah:
It is not permissible to use artificial nails, false eyelashes …, because of the harm that they do where they are attached to the body, and because they also involve deception and changing the creation of Allaah.
Fataawa al-Lajnah, 17/133
It says in Zeenat al-Mar’ah bayna al-Tibb wa’l-Shara’ (Woman’s adornment between medicine and sharee’ah), p. 33:
With regard to artificial eyelashes or the substances that are painted onto the natural eyelashes (i.e., mascara), the doctors say that they are made of a substance derived from nickel, or from some kinds of artificial rubber, and that they cause inflammation of the eyelids and make the eyelashes fall out.
And Allaah knows best.