Similarities:
* Composition: Both eyelashes and hair are primarily made of keratin, a fibrous structural protein.
* Growth Cycle: Both eyelashes and hair go through a growth cycle that includes a growth phase (anagen), a transition phase (catagen), a resting phase (telogen), and a shedding phase (exogen).
* Structure: Both have a similar basic structure: a root beneath the skin and a shaft that extends outward.
Differences:
* Length and Thickness: Eyelashes are much shorter and thicker than the hair on your head.
* Growth Cycle Duration: Eyelashes have a much shorter growth cycle than scalp hair. The anagen (growth) phase for eyelashes is about 4-8 weeks, while for scalp hair it can be several years. This is why eyelashes don't grow as long as head hair.
* Density: Eyelashes are much less dense than scalp hair.
* Medulla: Eyelashes often lack a medulla (the innermost layer of the hair shaft), which is more commonly found in head hair.
* Function: While both provide some protection, eyelashes have a more specialized function of protecting the eyes from debris and acting as a sensory warning system.
* Sebaceous Glands: Eyelashes have sebaceous glands (glands that secrete oil) associated with their follicles, which help to keep them moisturized. These glands are called Glands of Zeis. There are also sweat glands called Glands of Moll associated with eyelash hair follicles.
In Summary:
Eyelashes are a type of hair, but they have distinct characteristics that are suited to their specific function of protecting the eyes. They are shorter, thicker, and have a much shorter growth cycle than the hair on your head.