Eyelashes grow along the edge of the eyelid, and their function is to protect the eyes against dust and other environmental effects. It takes just a gentle touch to make the eye blink and close to protect the eye.

Number of eyelashes

The upper lashes are stronger, thicker, and more numerous than the lower lashes. The upper eyelid has 100-160 lashes on average, while the average number of lashes on the lower eyelid is 70-80. The number of lashes is very individual, but there are specific racial differences (e.g., people with Middle Eastern backgrounds usually have very dark, dense, thick, and long lashes, while Asians tend to have dark but sparse lashes growing straight instead of curving upwards). Like hair, eyelashes become weaker and thinner with age.

Lash layers

Lashes grow on average in 3-4 layers, and the layers are counted from the lowest to the highest when working professionally. This means that when you’re looking at lash extensions styling, the first layer is the one that’s the closest to the customer’s cheeks, and the highest is the one closest to the lash artist:

Lash length and strength

The average length of upper eyelashes is 7-10 mm. Still, you are likely to encounter customers with tiny natural lashes (below 5 mm) and customers who, naturally or more often with the help of a lash serum, have 13 mm or even longer natural lashes.

Lashes are also very different in diameter and strength. Most commonly, the thicker the lashes (, the wider their diameter), the stronger they are. This plays the most significant role in deciding how much volume can be added to them with extensions without causing damage and how long curling lotion should be processed during lash lamination.

Usually, the thinner the lashes, the weaker they are, BUT sometimes looks can be deceiving, and lashes that are not wide in diameter can be pretty strong. It’s not very common, but it does happen. It’s important to bear that in mind, for example, when doing lash lifting – some people’s lashes require extra processing times, although they might not seem strong initially.

The lashes in the eye’s inner corner usually are thinner and shorter than in the middle, where they are denser and longer. The lashes in the eye’s outer corner are generally thinner and shorter again but still longer and denser than in the inner corner. The strongest lashes are located from approximately the middle of the eye to the outer third:

The composition of an eyelash

Eyelashes consist of proteins that are produced in cells inside the follicle. The lash shaft also begins there. This cell maturing process is called keratinization. By the time the shaft protrudes from the skin, the cells are completely keratinized. Now, the lash only consists of keratinized protein cells which are not living cells. Lashes contain approximately 90% keratin and 10% pigment, water, and lipids. 

The structure of an eyelash

Each eyelash consists of the following:

  1. Cortex
  2. Medulla (the innermost part)
  3. Cuticles (scale-like cells forming the outer layer)

The coarser-textured cortex encases the medulla to ensure its strength and stability. The cortex is the most voluminous part of the lash. Pigmentation of lashes or hair results from melanin deposits in the cortex – the more deposits, the darker the hair. Blonde eyelashes are lashes without pigment deposits.


The cuticle is made of multiple dead cell layers, and it forms the outer part of the hair and protects its inner structures due to its high penetration resistance, maintaining the hair’s hydration. They overlap, forming scales like fish scales or roof tiles. These scales are affected by the different products we use in professional treatments: 

  1. Alkaline lash shampoos and saline water gently open cuticles 
  2. Easy Lift, Superdry, regular primers, and perming lotion fully open cuticles 
  3. Fixing lotion gently closes cuticles (not all the way) 
  4. Shine Repair fully closes cuticles (99-99.9%) 

There is a difference between Caucasian and Asian lash cuticular layers – on average Asian women have 8.0 +/- 1.2 and Caucasian females 6.5 +/- 1.1 layers of lash cuticles. 

Lashes and eyebrows are like hair because the more cuticles are closed, the healthier they look. This is because cuticles themselves are see-through – the color you see comes from the cortex’s melanin deposits. Think of cuticles as a row of glass panels behind one another. If there is a distance between the glass panels, you will not see through them well, but the view becomes very clear when you push them tightly together. It’s the same with cuticles – the tighter the cuticles are closed, the better you can see the melanin inside = lashes and brows look darker and shinier. 

This is one of the working mechanisms of Shine Repair – because it fully closes cuticles and makes lashes and brows look darker even without tinting:

This Brow Lift was done without tinting and finished with Shine Repair. Harsh products like old-school alcohol-based primers and strong lash-lifting products harm cuticles, burning some of them off. Burnt cuticles cannot keep moisture inside the lashes, so lashes will dry out and become brittle:

That’s why I recommend not using harsh primers and lash lift products!

Bonds that give lashes their strength and elasticity

Three types of bonds in the hair cortex keep the lash together and determine its form. The bonds prevent the lash from falling apart. The bonds in a lash are like ladders consisting of two vertical rails and several horizontal rungs. The rails are polypeptide chains linked by hydrogen, disulfide, and salt bonds. These chemical ‘ladders’ are, in turn, twisted into a spiral. The figure shows spiral polypeptide chains and the joints of hydrogen, disulfide, and salt bonds. 

Hydrogen, disulfide, and salt bonds play an important part in hair or lashes' wet, thermal, and chemical treatment.

Hydrogen (H) bonds are the most flexible of the three bond types and are easily broken by water and heat. Hydrogen bonds are broken during a hair wash, for instance. However, when the hair dries, the bonds are restored. Here is an example of hydrogen bond manipulation resulting in an altered appearance of the hair: setting your hair in rollers. Hair is usually set in rollers while wet. The hair is then held in position until it dries. As the hair dries, hydrogen re-bonding occurs, but in a new "shape." 

Hydrogen (H) bonds are responsible for up to 30% of the strength and up to 50% of its elasticity. Salt bonds are physical bonds that provide up to 35 % of the strength of a lash and up to 50% of its elasticity. They are easily broken by pH changes in the hair in both acid and alkaline directions. Readjusting the hair's pH will reform and stabilize these bonds. Salt bonds are formed when the positive end of the amino chain links to another amino acid's negative end. 

Disulfide = sulfur = S bonds bind sulfur atoms to two neighboring amino acids (cysteine) atoms. Compared to hydrogen and salt bonds, they occur almost two times less in hair. The more disulfide that occurs in the fiber, the curlier the hair. Disulfide bonds cannot be modified by water or heat, only chemicals. This is why during a lash lift, we focus on changing these bonds – these bonds are the strongest and will not lose their new shape in the presence of heat and water. Disulfide bonds are softened with curling lotion to give eyelashes a new form. Fixing lotion restores hydrogen and alt bonds and fixes the lashes' new shape by fixing the disulfide bonds' new arrangement.   

Lash growth

Eyelash cells develop in the lash follicles in the dermis of the skin. The cells split (lash growth phase) and then die, piling on each other, thus "growing out" of the skin. As a result, the visible eyelash is already dead and keratinized. That is why eyelash serums must be applied close to the eyelid since feeding the dead (protruding) part is futile. 

Lash growth is affected by many factors, such as :

  • hormone levels (for example, pregnancy and thyroid)  
  • medication (thyroid abnormalities have been found to associate with hair growth strongly) 
  • diet and vitamins 
  • amount of sunlight  
  • lash serums

Lashes are not only hormone-dependent structures, but they also produce a variety of hormones acting in: 

  1. Paracrine (a form of cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells) 
  2. Autocrine (a form of cell signaling in which a cell secretes a hormone or chemical messenger that binds to autocrine receptors on that same cell, leading to changes in the cell)  
  3. Or intracrine (a hormone that acts inside a cell, regulating intracellular events) manner, therefore, causing changes directly in the skin and hair biology.

Hair growth during pregnancy

If you have had children or pregnant customers, you have probably noticed a change in their lash retention and health. These are both affected by the changing hormones in women’s bodies during pregnancy and breastfeeding and the extra folates they take.

Folates stimulate hair follicle cells’ rebuilding, prevent hair from falling out, and regulate sebum glands functioning. Here are some great folate sources: kale, asparagus, white beans, Brussels sprouts, green peas, beets, cod, halibut, eggs, and poultry liver.

Thyroid abnormalities

The thyroid hormone influences the activity of all cells in humans. It is, therefore, not unexpected that hair follicle activity is affected by hypothyroidism or hyperthyroidism. Hypothyroidism causes hair to become dull, brittle, and coarse with a reduced diameter and areas with hair loss. Hyperthyroidism can cause hair to break off and become shorter and cause Alopecia.

It has also been found that skin thickness contributes positively to vitamin D status, so using medication that causes skin thinning will also decrease vitamin D status. Also, age plays a part because aging reduces the skin’s efficiency in vitamin D synthesis.

For more info, visit:

Lash shedding

Lash growth cycles are affected by many factors, and changes in those can trigger a difference in the lash growth cycle. The most significant annual shift in lash growth cycles is spring/fall lash shedding, which is subjected to many lash industry discussions.

When we enter the cold season, there is not as much Sun as in the summer, so our bodies' vitamin D levels drop significantly. Vitamin D deficiency can lead to hair loss as sunlight is the primary determinant of our bodies' vitamin D status. This is much more noticeable in areas where the changes in seasons are more significant, so the latitude where you live plays a big part in whether you will encounter these changes. This is important to remember because if you live in an area with lots of Sun throughout the year, you will not likely notice a significant difference in your customers' lash cycle.

Looking at the location of lash artists who argue against seasonal shedding, you will see that most live in sunny areas. Since they have yet to encounter these changes, they believe it does not exist.

For example, where I live – in Tallinn, Estonia (59.4370° N) doctors recommend taking high levels of extra vitamin D from September to April due to the lack of sunshine and, therefore, vitamin D levels in our bodies.

Studies conducted on model animals show that the vitamin D receptor plays a significant role in the hair follicle cycle, especially in anagen initiation. The first study performed systematically in a representative number of women was conducted over six years to test the hypothesis that periodicity in hair shedding reflects seasonal changes in human hair growth. The study concluded in 2009 and confirmed the findings of former authors that seasonality DOES affect hair growth and shedding.

It does not affect everyone, though, and researchers will surely do more studies on hair growth and shedding. When you start Googling the subject, you will find that "more research is needed" is usually said about this matter. It does NOT mean that these seasonal changes are a hoax; it just means that researchers need to do more studies to confirm their findings. Doing studies on women is very expensive due to hormonal changes, so men are usually generally preferred.

Please see the article from the journal Dermatology for more information:

How to tell the difference between lousy retention and lash shedding? 

It is relatively easy to tell the difference. You can recognize that lashes are going through a transition by the following telltale signs: 

  • Customers come to infills with many more anagen lashes than usual 
  • Customers have fewer telogen lashes than usually  
  • The remaining extensions have grown out more than usual 
  • During infills, some telogen lashes fall off when you touch them with tweezers or brush through 

It's important not to confuse it with Blepharitis, though, as these two points are also characteristic of Blepharitis. You can tell the difference by the symptom of Blepharitis that is not characteristic of the seasonal shed – white/yellowish gunk on the eyelashes' roots.  

For more info, visit:  

Special thanks to Crystal from Rebel Lash & Beauty for helping me gather information on this topic. 

Growth cycles

Eyelashes have a lifetime of about three months – an active growth phase that is followed by a rest period, and then the lash falls out and is replaced by a new eyelash. Unfortunately, eyelashes do not grow in sync, so we lose lashes daily (about 2-5 per day from both eyes). Usually, people do not notice this because the eyelashes are fine and small. Still, the life cycle of the eyelashes should be mentioned to new customers because eyelashes with an extension are more noticeable. Thus when the client loses them, it may seem that she is suddenly losing a lot of lashes.


The growth cycle also affects how long a lash lift will look fresh on the customer.

Suppose most lashes were in the final phase of telogen during lifting (i.e., immediately before falling out). In that case, the result looks excellent but deteriorates quickly as the lashes in telogen start to fall out. The lashes have fallen out sooner than usual or even en masse for the customer. In this case, the technician should always explain to the customer why that has happened and that the lashes have NOT fallen out sooner than expected. It looks like they have, as the shedding of straight (i.e., not lifted) lashes is less noticeable than that of curled lashes.

Lash cycles are complicated (if not impossible) to notice with new customers as you could not know what her “normal” lashes look like. When you have a repeat customer, it would be a good idea to compare pictures of her natural lashes to understand her cycle and time lifts accordingly for a longer-lasting result.

Lashes have a life cycle consisting of three phases: the active growth phase (anagen), the transition phase (catagen), and the resting phase (telogen). After telogen, the lash falls out, and the life cycle resumes with a new lash in the anagen phase. The daily growth rate of a lash is 0.12-0.15 mm. The length of a lash is less than 13 mm, as the growth rate is slower and the anagen phase is much shorter than in hair.

  1. The Anagen phase is also called the growth phase. This is the phase when lashes are actively growing, and it lasts between 30 and 60 days. Only about 40 percent of the upper lashes and 15 percent of the lower lashes are in the anagen phase at any given time. Each lash will grow to a specific length and then stop.
  2. In professional slang, anagen lashes are called “baby” lashes. When applying extensions to these baby lashes, you need to pay special attention not to overload the growing eyelashes with extensions to prevent damaging them. Usually, we do not recommend using a thicker diameter than 0.10 mm on baby lashes.
  3. The Catagen phase is also known as the transitioning phase. During this phase, the lash stops growing, and the hair follicle shrinks. If an eyelash falls out or is plucked out during this phase, it won’t grow back right away because the follicle needs to complete the catagen phase before moving on to the next one. The Catagen phase lasts between two and three weeks.
  4. The Telogen phase is also called the resting phase. The hair is keratinized, and the growth stalls until it stops. This phase can last more than 100 days before the eyelash falls out and a new one begins to grow. Because each lash is in its phase of the growing cycle, it’s normal for a few lashes to fall out most days. It typically takes between four and eight weeks to replace an eyelash fully. Usually, about 50% of upper lashes are in the telogen phase at any given moment.

Growth directions

Lashes grow either upwards, more or less straight or downwards. The growth direction of lashes determines the exposure time for curling lotions and the recommended curl choices for extensions:

  • Customers with noticeably upward lashes usually don’t use a lash lift, as they do not need them. If anything, they would ask for a straightening treatment instead.

Before straightening‏‏‎‎‏;‏‎‎‏‏‎ ‎‏Photo credit:

After straightening‏‏‎‎‏;‏‎‎‏‏‎ ‎‏Photo credit:

  • Most people have slightly upward-growing, more or less straight, or somewhat downward-growing lashes. The recommended processing times should be followed for those lashes.
  • Noticeably downward-growing lashes require longer processing times than recommended. Depending on the brand, usually 1-5 minutes extra processing time for the curling lotion is needed because it takes more effort to lift very downward-growing lashes to the same level as expected with straight-growing lashes.
  • Lashes with uneven growth direction (i.e., some lashes growing straight) and the rest (usually in the outer corner) growing downward should be treated with Easy Lift for a precise result, or different curling lotion processing times should be used if you work with another brand. If you use the exact curling lotion processing times on the whole lash line, the outcome will be uneven – downward-growing lashes will not be as lifted as the rest.

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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