To become a qualified and professional lash technician, it's important to know some basic knowledge about eyelashes.
Fun fact: Eyelashes are the most pigmented of all human hair, which is why they do not turn gray with age and rarely whitens (unlike the hair on our head)。 
1. Eyelash Anatomy
The anatomy of eyelash and hair are similar in some aspects. They both have (1) a shaft that extends outside the skin, which is the visible part, (2) a root that is under the skin and (3) a bulb, which is the enlarged terminal portion. (Fig. 1)
Fun quiz 1: How many lashes does a human have on the upper eyelid?
Answer: The human upper eyelid contains 90-160 lashes dispersed on 5 to 6 row! , , 
Fun quiz 2: How many lashes does a human have on the lower eyelid?
Answer: The human lower lid has 75-80 lashes scattered in 3 to 4 rows! , , 
2. Eyelash Structure:
From outside to inside:
The outermost impermeable layer of lash, offering protection to the internal structures.
Ensures the strength and stability of lash, containing melanin, which results in pigmentation of lash.
The innermost portion, consisting of loose cells.
(Fig. 2) 
Fun quiz 3: What is the longest length a lash can grow usually?
Answer: The lash length rarely exceeds 12 mm. 
3. Eyelash Growth Cycle:
A complete growth cycle of eyelashes consists of three distinct phases:
(1) Anagen (The growth phase; 4-10 weeks)
(2) Catagen (The degradation/transition phase; 2-4 weeks)
(3) Telogen (The resting phase; 4-9 months)
A complete cycle of eyelash is from 4 to 11 months.   
The resting phase lasts so long, that 85-90% of lashes are in their resting phase.
Fun quiz 4: How many mm can a lash grow daily?
Answer: The average growth rate of a lash is 0.12-0.14 mm per day. , 
Now you mastered the basic knowledge of eyelashes. Next step: get some professional tools and materials. Purchase professional lash extension products on ARISONLASHES.com