Biology of eyelashes

Most of us have 90 to 160 eyelashes on the upper lash line, distributed in five to six rows. The lower lash line can have up to 80 lashes.

Each lash consists of a hair shaft (the lash you see), a root under the skin, and a bulb from which new hairs begin to grow. The bulb is connected to a skin papilla (blood supply) that nourishes the lashes so they can grow.

Although we love eyelashes for their dramatic framing, they also have a purely functional purpose. The lashes are very sensitive to touch, and when an object or particle touches them, they send automatic signals to the brain to close the eyes. Lashes also help filter sunlight and protect the eyes from any unwanted dirt or sweat.

Interesting fact: eyelashes are the most pigmented of all human hairs, and they lack a special gene, so they do not turn grey with age (unlike eyebrow hairs, for example).

The cycle of eyelash growth

Eyelashes go through three phases in their growth cycle: anagen (active growth), catagen (transition) and telogen (rest).

The full cycle can take from four to eleven months.

1.  ANAGEN (ACTIVE GROWTH) PHASE. At this stage, the hair attaches to the skin papillae (blood supply), which “nourish” the eyelashes and help them grow. Around 35-40% of the upper lashes (and 15% of the lower lashes) will be in the growth phase at simultaneously, – this ensures that you don’t lose all your lashes at once when the shedding phase begins. The anagen phase lasts from 4 to 10 weeks, when lashes grow at a rate of 0.12 to 0.14 mm per day. Keep in mind that only 40% of your lashes can be in this phase at simultaneously, so when you start using lash serums, for example, you will see increased length/new lashes on a portion of your lashes while the other 60% of the cycle goes through other phases.
2. CATAGENIC (TRANSITIONAL) PHASE. In this phase, the hair follicle shrinks, the blood supply stops, and the lash stops growing. Called the “transition phase”, the eyelashes retain the length gained in the anagen phase while waiting for the next phase. This stage lasts 2–3 weeks. Another interesting fact: if an eyelash falls out unnaturally (for example, it was pulled out) during this phase, the follicle remains “free” – it completes this phase and moves on to telogen. This means that you will have an “empty spot” until the follicle reaches the anagen phase again.
3.  TELOGEN (RESTING) PHASE. At this stage, the eyelashes are dormant and resting, while new hairs begin to form inside the follicle and the old ones fall out naturally. This stage lasts from 3 to 4 months before the lash falls out and re-enters the active growth phase.

Approximately 50% of lashes are in this phase at simultaneously.