Eyelashes can be lost when mascara is applied or when an eyelash curler is used, or they may simply fall out. Like any hairs, it is normal for eyelashes to fall out and to then be replaced by other hairs growing in their places. However, eyelashes do have cycles that are different from the cycles of scalp hairs.
Eyelashes are an important safety system for the eyes. They keep dust from falling into the eye. They also alert the eye that something is moving toward it before it actually gets there, allowing the eye time to close. This makes it important to retain eyelashes if possible. But aside from their practical use, eyelashes are also esteemed as an attractive part of the face.
All human hairs go through three stages during their growth and development. One stage is anagen. This is the active, growing phase. For eyelashes, this phase lasts 30 to 45 days. Eyelashes are short because this phase is far shorter than the two- to six-year growth phase of scalp hairs. During this phase, the hair will keep growing and will not fall out unless pulled, plucked or otherwise forced out.
Another phase of hair growth is the catagen phase. This phase is a stage of transition. An eyelash in this phase is no longer growing. The sheath of the outer root of the eyelash shrinks during this phase and attaches itself to the hair's root. The follicle is not making hair during this phase. If the eyelash falls out during the two to three weeks of this phase, it will not grow back until after the follicle's catagen phase is over.
The phase in which most hairs, including eyelashes, fall out is the telogen phase. This is the hair's resting phase. A hair in this phase will rest for about 100 days before eventually falling out. Tugging gently on an eyelash that is in this phase may result in it coming out sooner than it would have on its own. Losing an eyelash during this phase means that new eyelashes will grow in faster because the growth cycle of the hair was not interrupted.
Pulling out eyelashes or plucking them means that the eyelashes that were in the active growth or transitional phases will not be equipped to start new growth as quickly as one that was lost naturally at the end of its resting stage. But, no matter what phase the eyelash is lost in, it will eventually grow back. It can take weeks or months before you have a new eyelash, depending on when it was lost.