Eyelashes are a form of hair, sharing fundamental biological characteristics with hair found elsewhere on the human body. While they serve a distinct purpose and possess specialized features, their underlying structure and growth mechanisms align with the broader definition of hair.
What Makes Hair, Hair?
Hair is a protein filament that grows from follicles embedded within the dermis layer of the skin. Its primary component is keratin, a strong fibrous protein also found in nails and the outer layer of skin. Each strand of hair consists of a hair shaft, the visible part above the skin, and a hair root, which is anchored within the follicle.
The hair shaft is composed of three main layers: the medulla, the cortex, and the cuticle. The cortex provides strength and color, containing melanin pigments that give hair its natural hue. Hair follicles have a bulb at their base, where cells actively divide to produce new hair, nourished by a rich blood supply.
Eyelashes: A Specialized Form of Hair
Eyelashes grow from follicles along the edges of the eyelids. They exhibit unique characteristics tailored to their location and function. Eyelashes are shorter and coarser than scalp hair, with an average length ranging from 7 to 8 millimeters, rarely exceeding 10 millimeters.
Their primary function is to protect the eyes from external elements. Eyelashes act as a barrier, catching dust, debris, and small particles before they can enter the eye. They also help regulate the evaporation of the tear film on the cornea and shield the conjunctiva from excessive light and ultraviolet radiation. Eyelashes are highly sensitive to touch, triggering the blink reflex when an object approaches the eye, providing an immediate protective response. This specialized sensory role, coupled with their protective barrier function, highlights their adaptation as a unique form of hair.
The Eyelash Growth Cycle
Like all hair, eyelashes undergo a distinct growth cycle comprising three phases: anagen, catagen, and telogen. The anagen phase is the active growth period, during which the hair follicle is connected to a blood supply that nourishes the lash. For eyelashes, this phase is relatively short, lasting between 30 to 45 days, which limits their potential length.
Following the anagen phase is the catagen phase, a transitional period lasting about two to three weeks. In this stage, the eyelash stops growing, and the hair follicle shrinks, detaching from its blood supply. The telogen phase is a resting and shedding phase that can last around 100 days. During this time, the old lash rests before it naturally falls out, making way for a new lash to begin its growth cycle in the same follicle. The entire eyelash growth cycle can span from four to eleven months.