Eyelashes grow just like any other hair on your body. Your genes carry a specific growth cycle to keep them growing regularly. Each hair follicle grows many hairs over your lifetime. On average, each follicle grows 20 new hairs. The growth phases are staggered to prevent periods of eyelash baldness when the growth cycle stops.
Anatomy and Function
You have around 90 to 150 eyelashes on the upper lid and 70 to 80 on the lower lid. They typically grow just under 1/2-inch long and have nerve sensors that cause the eyelid to shut when a speck of dust hits one. Aesthetically, they frame the eyes and they filter out foreign objects and keep them away from the eye.
Anagen, the active growth phase, varies in length between the sexes and from person to person, but usually ranges from 30 to 45 days. The length of this phase determines how long each hair grows. It's genetic, and you can't change it to make them grow faster or thicker. Only 40 per cent of the upper lashes and 15 per cent of the lower lashes are in active growth at any one time.
Catagen refers to the intermediate or resting phase that takes place after the anagen phase. During this lag phase, growth stops and no pigment is made. The base of the follicle shrinks up towards the surface of the skin. The phase lasts between two and three weeks.
Telogen, the shedding phase, is the longest, lasting three to four months. New hair starts to grow from the follicle; as it pushes higher, the old hair will shed naturally. Since each eyelash is on its own schedule, you do not have to worry about all of them falling out at once.
What if you pull an eyelash, will it grow back? Yes, eyelashes will regrow, but it take up to two months to fully replace the eyelash depending on where it was in the growth cycle. Be careful because if you lose a clump of them, each one will take a different amount of time.
Many myths revolve around stimulating eyelash growth. Some believe that if you cut the tips off the lashes they will continue to grow. Many eyelash growth products are available over the counter, but none have scientific backing. Bimatoprost ophthalmic solution--prescribed under the name Latisse--is believed to affect the anagen phase by increasing the length of this phase and increasing the number of hairs in the growth phase. According to the Latisse website, "The exact way it works is unknown."