Anatomy – Ultimate Guide to Lash & Brow Artistry | Ruthie Belle


by Martin Pork

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 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 certain racial differences (e.g., people with Middle Eastern background 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 layers

Lash length and strength

The average length for upper eyelashes is 7-10 mm, but you are likely to encounter both customers with tiny natural lashes (below 5 mm) and customers who either 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 quite 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 to begin with.

The lashes in the eye’s inner corner usually are thinner and shorter than in the middle, where they are denser and longer. In the eye’s outer corner, the lashes 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 to the eye to the outer third:

The composition of an eyelash

Eyelashes consist of proteins which 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 is made up of:

  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. 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, Adhesive 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 just like hair in the sense that 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 distance between the glass panels, you will not see through them that well, but the view becomes very clear when you push these panels 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, just finished with Shine Repair. Using 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 recommended that you don’t use harsh primers and lash lift products!

Bonds that give lashes their strength and elasticity

Three types of bonds situated in the hair cortex keep the lash together and determine its form. Basically, the bonds prevent the lash from falling apart. The bonds in a lash are like ladders consisting of two vertical rails and a number of horizontal rungs. The rails are polypeptide chains linked to each other by hydrogen bonds, disulfide bonds 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 in them. 

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

Hydrogen (H) bonds are the most flexible of the three bond types and they are easily broken by water and heat. Hydrogen bonds are broken during a hair wash, for instance. When the hair dries, the bonds are restored again. 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 the 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 direction. Readjusting the hair’s pH will reform and stabilize these bonds. Salt bonds are formed when the positive end of an amino chain links to another amino acids negative end. 

Disulfide = sulfur = S bonds bind sulfur atoms to two neighboring amino acid (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 the reason why during Lash Lift we focus on the modification of these bonds – these bonds are the strongest and will not lose the new shape in the presence of heat and water. Disulfide bonds are softened with curling lotion so that we can give eyelashes a new shape. Fixing lotion restores hydrogen and alt bonds and fixes the new shape of the lashes by fixing the new arrangement of their disulfide bonds.   

Lash growth

Eyelash cells develop in the lash follicles located in the dermis of the skin. The cells split (lash growth phase) and then die, piling on top of each other, and thus “grow out” of the skin. The eyelash visible to the eye 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 strongly associate with hair growth) 
  • 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 overall lash health. These are both affected by the changing hormones in women’s bodies during pregnancy and breastfeeding and also the extra folates they take.

Folates are responsible for stimulating hair follicle cells’ rebuilding, preventing hair from falling out, and regulating sebum glands functioning. Here are some great folate sources: kale, asparagus, white beans, Brussel 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 as well as areas with hair loss. Hyperthyroidism can cause hair to break off and to become shorter; it can also cause Alopecia.

It has also been found that skin thickness contributes positively to vitamin D status, so using medication that causes thinning of the skin will also decrease vitamin D status. Also, age plays a part because aging reduces 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 change in the lash growth cycle. The most significant annual shift in lash growth cycles is spring/fall lash shedding, which has been subjected to many lash industry discussions.

When we enter the cold season, there is not as much Sun as in the summer, so vitamin D levels drop significantly in our bodies. 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 are likely to encounter these seasonal changes or not. This is very important to remember because if you live in an area with lots of Sun throughout the year you are not likely to notice a significant change in your customers’ lash cycle.

If you look at the location of lash artists who argue against seasonal shedding, you will see that the majority live in sunny areas. Since they haven’t encountered these changes, they believe that 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 the course of 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 usually, „more research is needed” is said about this matter. It does NOT mean that these seasonal changes are a hoax; it just means that researchers find that they need to do more studies on this to confirm their findings. Doing studies on women is very expensive due to their hormonal changes, so usually, unfortunately, men are preferred for these studies.

Please see the article from journal Dermatology for more information:

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

It is not very difficult 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  
  • 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 3 months – an active growth phase which is followed by a rest period, and then the lash falls out and is replaced by a new eyelash. Eyelashes do not grow in sync, so we lose lashes every day (about 2-5 per day from both eyes). Usually, people do not notice this happening 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.

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

Suppose the majority of lashes were in the final phase of telogen during lifting (i.e., immediately before falling out). In that case, the result looks great but deteriorates quickly as the lashes in telogen start to fall out. For the customer, it looks as if the lashes have fallen out sooner than normal or even en masse. 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 normal. It just looks like they have, as the shedding of straight (i.e., not lifted) lashes merely is less noticeable than that of curled lashes.

Lash cycles are quite difficult (if not impossible) to notice with new customers as you could possibly 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 over time 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 rarely exceeds 13 mm, as the growth rate is slower and the anagen phase much shorter than in hair.

  1. 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.
    In the 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.
  2. 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 it can move on to the next one. Catagen phase lasts between two and three weeks.
  3. 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 individual lash is in its own 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 fully replace an eyelash. 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:

  1. Customers with noticeably upward lashes usually don’t use Lash Lift, as they have no need for it. If anything, they would ask for a straightening treatment instead.

Before straightening‏‏‎‎‏;‏‎‎‏‏‎ ‎‏Photo credit:

After straightening‏‏‎‎‏;‏‎‎‏‏‎ ‎‏Photo credit:

  1. Most people have slightly upward-growing, more or less straight or slightly downward growing lashes. The recommended curling times should be followed for those lashes.
  2. Noticeably downward-growing lashes require longer processing times than recommended. Depending on the brand, usually 1-5 minutes extra processing time of 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.
  3. 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 an even result, or different curling lotion processing times should be used if you work with a different brand. If you use the same 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.