What Are Eyelash Extensions?

Course: Eyelash extensions course from A to Z · Module 1 of 10

Welcome to the Lash Canarias eyelash extension course. This first module starts with a simple question, what are eyelash extensions, and lays the foundations for everything that follows: the eye and eyelid you will be working on and, above all, how a natural lash is born, grows and sheds. Once you understand the growth cycle, it becomes obvious why extensions fall out, why infills are needed and why bonding lashes badly can damage the follicle.

Before you start: this online course is for educational and information purposes only. It does not replace hands-on, in-person training with a qualified educator, and it does not lead to any certificate or qualification. Always follow the manufacturer’s instructions for every product you use.

Module objectives

Explain what eyelash extensions are and how they differ from strip lashes.
Identify the parts of the eyelid and lid margin that matter in day-to-day lash work.
Know how many lashes an eye has, how they are arranged and how long they grow, according to the scientific literature.
Understand the three phases of the growth cycle (anagen, catagen and telogen) and what they mean for your work.
Appreciate why the eye area calls for more caution than most other beauty treatments.

What are eyelash extensions?

Eyelash extensions are fibres, usually synthetic, bonded one at a time (or as small fans) onto the natural lashes with a dedicated adhesive. The American Academy of Ophthalmology’s EyeWiki describes them as synthetic fibres, such as polyester, attached to the natural lashes, and notes that they are typically topped up every 2–3 weeks as needed.

The key difference from strip lashes is where they attach. A strip is glued onto the skin of the eyelid and taken off the same day. An extension is bonded to one specific natural lash, never to the skin, and stays on until that natural lash sheds as part of its normal cycle. That is why professional technique is built around isolation: separating each natural lash and placing the extension on that lash alone.

The main techniques covered in this course

Technique	What goes on each natural lash	Covered in
Classic (1:1)	One extension	Module 6
Russian volume and mega volume	A fan of several fine extensions	Module 7
Hybrid	A mix of classic and volume	Module 7

Extensions are designed so the client can skip mascara, but they are not risk-free: you are working with adhesives a few millimetres from the eye, in one of the most sensitive areas of the body. That is why this course spends whole modules on consultation, hygiene, products and preparation before it gets anywhere near technique.

Basic anatomy of the eye and eyelid

You don’t need medical training to be a lash artist, but you do need to know what you are touching and why some moves are off-limits. These are the structures that matter most in practice.

The eyelid

Eyelid skin is different from scalp skin. According to the review by Aumond and Bitton (Journal of Optometry, 2018) and the StatPearls chapter on eyelashes, eyelid skin has only two layers (epidermis and dermis), whereas the scalp also has a hypodermis. Lash follicles are anchored in the dermis.

Inside the lid sit the tarsal plates, dense connective tissue that gives the eyelid its firmness. StatPearls notes that the meibomian glands sit within them and produce the lipids that help stabilise the tear film. The practical takeaway: pads and tape must never press on or cover the waterline, and no product should reach the inner rim of the eyelid.

The lid margin and its glands

Next to each lash follicle the literature describes two types of small gland:

Glands of Zeis: sebaceous glands that release sebum into the follicle. This is part of the reason natural lashes carry oil, and why thorough cleansing matters so much for retention.
Glands of Moll: apocrine glands found only in the eyelids.

StatPearls also describes the lid margin as one of the most sensitive parts of the human body, surrounded by free nerve endings. That explains why any tug, adhesive fumes or a rubbing pad is felt far more there than elsewhere.

What a lash artist must never forget

The client’s eyes stay closed for the entire treatment.
Adhesive, primer and remover must never touch the surface of the eye or the skin.
Lash follicles have no arrector pili muscle, so they cannot “defend” themselves against excessive pulling.

The natural lash: how many and what they are like

Knowing the normal figures helps you assess each client and set realistic expectations.

Figure	Upper lid	Lower lid
Approximate number of lashes	90–160	75–80
Rows they sit in	5–6	3–4
Follicle depth	2.4 mm	1.4 mm

Sources: Aumond and Bitton (2018) for number and rows; StatPearls for follicle depth.

A few more useful facts from the same sources:

A lash has a visible shaft, a root and a bulb. The cortex, rich in keratin and melanin, gives it strength; the outer cuticle consists of 7–10 layers of overlapping scales.
Lashes grow by roughly 0.12–0.14 mm a day and rarely exceed 12 mm in length.
Every lash has a curve, starting at the bulb itself, although the degree varies from person to person.

The range is wide: one client may have almost twice as many upper lashes as another. So there is no point promising “a fixed number of extensions” in a full set; it depends on how many healthy natural lashes each person has.

The lash growth cycle

Every lash goes through three phases. The crucial point is that not all lashes are in the same phase at once: on any given lid there are lashes growing, lashes in transition and lashes about to fall out.

Anagen (growth phase)

This is the active growth phase. StatPearls and the Aumond and Bitton review put it at 4 to 10 weeks. A study by Thibaut and colleagues (British Journal of Dermatology, 2010), which followed four volunteers weekly for nine months, calculated an average of 34 ± 9 days.

Anagen lashes are shorter and finer, often with a lighter tip. You need to spot them during consultation, because they cannot carry the same weight as a mature lash.

Catagen (transition phase)

The lash stops growing and the follicle shrinks. StatPearls estimates this phase at about 15 days.

Telogen (resting and shedding phase)

The lash stays in the follicle without growing until it sheds and a new one starts its anagen phase. The sources disagree here: StatPearls gives 4 to 9 months for telogen and 4 to 11 months for the whole cycle, while the Thibaut study measured an average full cycle of 90 ± 5 days in its small sample. The honest takeaway is the general picture: the cycle lasts months, varies between individuals, and you cannot tell by eye how long any one lash has left.

Phase	What happens	Duration in the sources reviewed
Anagen	The lash grows	4–10 weeks (StatPearls, Aumond and Bitton); average 34 ± 9 days (Thibaut 2010)
Catagen	Growth stops and the follicle shrinks	About 15 days (StatPearls)
Telogen	Resting until natural shedding	4–9 months (StatPearls); the full cycle measured by Thibaut was 90 ± 5 days

StatPearls adds that a plucked lash takes around 8 weeks to grow back.

What the cycle means for your work

This is the practical heart of the module. Everything above translates into clear working rules:

Extensions shed with the natural lash. When a lash reaches the end of its cycle, it falls out with the extension still attached. That loss is normal and is the reason infills exist (Module 9).
One extension (or one fan) per natural lash. If you bond two natural lashes together and they are at different stages, the growing lash will pull on the resting one. Besides discomfort, this puts traction on the follicle.
Weight must match the natural lash. A young, fine lash cannot carry what a mature one can. You will choose diameter and length lash by lash, as covered in Modules 4, 7 and 8.
Ongoing traction has consequences. The AAO EyeWiki lists traction alopecia (loss of natural lashes) among the complications linked to extensions.
The sensitivity of the area demands extra care. A Japanese retrospective study (Amano and colleagues, Cornea, 2012) reviewed 107 patients who visited eye clinics with complaints after extensions; the most frequent causes were keratoconjunctivitis from adhesive or remover and allergic blepharitis from the adhesive.

Common mistakes

Assuming all of a client’s lashes are the same and using one length and diameter throughout.
Overlooking anagen lashes (short and fine) and loading them with extensions that are too heavy.
Promising a fixed retention time without explaining that it depends on each person’s natural cycle.
Working while the client’s eye is slightly open, or with products close to the waterline.
Believing this online course alone is enough to start working on clients without supervised practice.

Kit to follow along

You don’t need to buy anything for this theory module, but if you want to start getting familiar with the tools, browse our lash extensions, professional tweezers and accessories. Module 2 goes through each tool in detail.

Module summary

Extensions are fibres, usually synthetic, bonded to isolated natural lashes and never to the skin.
Eyelid skin is thin; the lid margin holds glands (Zeis, Moll and, in the tarsus, meibomian glands) and many nerve endings.
The upper lid has around 90–160 lashes in 5–6 rows; the lower lid around 75–80 in 3–4 rows.
Lashes grow roughly 0.12–0.14 mm a day and rarely exceed 12 mm.
The cycle has three phases (anagen, catagen and telogen); the sources give different durations, but it lasts months and is asynchronous.
That cycle explains normal extension shedding, the need for infills and the rule against sticking lashes together.

Self-assessment

What is the main difference between an eyelash extension and a strip lash?

An extension is bonded to an isolated natural lash, without touching the skin, and lasts until that lash sheds naturally; a strip lash is glued to the eyelid skin and removed the same day.

Roughly how many lashes does the upper lid have, according to the literature reviewed?

Between 90 and 160, arranged in 5–6 rows, according to the Aumond and Bitton review (2018).

Which phase is a short, fine, still-growing lash in, and what does that mean for your choice of extension?

It is in anagen. It is a young lash that cannot carry the same weight as a mature one, so the extension must be proportionate to its diameter and length.

Why should two natural lashes never be bonded together?

Because each may be at a different stage of the cycle; as one grows and the other doesn’t, the follicle is pulled, causing discomfort and risking damage to the natural lash.

Why does lash cleansing matter from an anatomical point of view?

Because the sebaceous glands of Zeis release sebum into the follicle, and oil on the natural lash interferes with adhesive bonding.

Sources

Note: this module is for education and information only and does not replace hands-on, in-person training with a qualified educator. Always follow each product manufacturer’s instructions and, if a client reacts (intense itching, swelling, pain), remove the product and advise them to see a healthcare professional.

Buy the course supplies

All the supplies for this course are available at Lash Canarias:

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