Eyelashes aren't just a pretty feature on the body; they have a very specific and important function. Eyelashes are designed to prevent objects from getting in the eyes. Each eyelash is actually a sensory hair that reflexively shuts the eyelid whenever it is touched by dirt, dust or anything else that could possibly get in the eye. The upper lid typically has about 90 to 150 lashes on it, while the bottom has between 70 and 80 lashes. Most eyelashes grow to be about 10 mm long (just over 3/8 inch).
Eyelash and Hair Growth
Although it may not seem like it, hair growth is a preset function of the body. Every hair on your body follows a specific growth cycle and will grow to a specific length. Hair follows a three-phase growth cycle and eventually falls out, which is typically nothing to worry about. In fact, body hair, including eyelashes, completely replaces itself every few years.
Anagen (Growth) Phase
The anagen phase is also called the growth phase. This is the phase when lashes are actively growing, and it lasts between 30 and 45 days. Only about 40 percent of the upper lashes and 15 percent of the lower lashes are in the anagen phase at any one time. Each lash will grow to a specific length and then stop.
Catagen (Transition) Phase
The catagen phase is also known as the transition phase. During this phase, the lash stops growing and the hair follicle shrinks. If an eyelash falls out or is plucked out during this phase, it won't grow back right away because the follicle needs to complete the catagen phase before it can move on to the next one. This phase lasts between two and three weeks.
Telogen (Resting) Phase
The telogen phase is also referred to as the resting phase. This phase can last more than 100 days before the eyelash falls out and a new one begins to grow. Because each individual lash is in its own phase of the growing cycle, it's normal for a few lashes to fall out most days. It typically takes between four and eight weeks to fully replace an eyelash.