THE NAIL UNIT

Nail Unit

The Nail Unit

A thorough understanding of the nail unit is absolutely essential for a professional nail technician. Information about the structure and physiology of this area of the body has been sketchy in the past. Now there has been so much research that we are able to understand it so much better. Essential read to get an even better understanding is Nail Structure and Product Chemistry by Douglas D Schoon.
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A basic understanding of how the skin is structured and how it grows should help with understanding how finger nails and toenails are formed as a nail unit. Like the hair follicle, the area where the nail starts life is a fold of the epidermal layer where the skin cells are instructed by their nucleus to make certain adaptations. In the skin, they become keratinised to form the flattened cells of the stratum corneum. In the hair, they are keratinised and adapted to create a hair shaft. In a nail, they are also keratinised and form flat layers and make up a hard nail plate. Like the upper layer of the epidermis (stratum corneum) and hair, the nail is non-living. Like hair it can be cut without any sensation. 
The function of the nail 
All species of primate have nails. They are linked to the evolution of using hands (and feet) to manipulate objects. Humans are able to use the thumb and forefinger in a pincer movement. The higher primates, such as gorillas and chimpanzees, have hands that are very similar to ours with fingerprints and perfect nails., but they cannot manipulate their thumbs as well as we can. There is a theory that this arrangement of our thumbs gave our species the opportunity to evolve faster, as we were able to use a wider variety of tools.
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Nails are on the ends of our fingers for several reasons and are not just there to paint or chew! They provide a rigid support for the end of the finger, allowing us to pick things up more easily, and they protect the end of the finger and the last bone from countless knocks. The last bone in each finger and toe is actually quite delicate and needs this protection.
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Nails start to form in an unborn baby very early in the gestation period and by 17-20 weeks are fully formed. Nails will even appear to 'grow' for a short period after death, as the cycle of adaptation of the skin cell's and keratinisation will continue, once it has started, without any nourishment from the blood supply, plus the surrounding skin shrinks back.
The structure of the nail
Matrix This is the most important area of the nail unit. It is directly under the proximal nail fold or mantle and it is where cells are incubated to form the nail plate. New cells push the older cells forward and this is the growth pf the nail plate. Keratin is a protein formed of amino acids that is within each cells. As the cells become keratinised, they bond together and lose the other cell contents. Unlike in the epidermis, where the bonds break down and the cells are shed, the bonds in a newly forming nail plate are much stronger and the lipid content is retained. The keratinised cells form layers, or lamellae, and several of these bond together to form the nail plate. As the cells move forward they become more compact and the nail plate becomes harder as it moves towards the free edge.
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The shape and size of the matrix will determine the thickness and width of the nail. The matrix extends from the base of the nail down towards the first joint. The longer the matrix, the thicker the nail. Thin nails will tend to have a short matrix. The width of the nail will be determined by the width of the matrix. Naturally thin (or thick) nails are hereditary; however, a lot can happen to them once they are grown to change this characteristic. There is no scientific evidence that malnutrition can make a nail weaker.
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The matrix is divided into three parts; front, middle and back. Each area produces slightly different nail cells that all come together to create a nail plate that is flexible, tough and resistant to chemical penetration. 
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The central area is fibrous so gives the nail flexibility. The upper and lower layers protect the flexible layer and seal it to maintain the integrity of the nail plate.
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The upper layers of the nail plate are created by the proximal part of the matrix so are older and have had longer to keratinise. This makes the layer harder and less able to allow penetration by chemicals.
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Damage to these layers seriously undermines the structure of the whole nail plate. Damage can so easily occur from over-filing, buffing and improper removal of coatings. The implications are wide-ranging. Not only will damage weaken the nail plate as a whole, it will also restrict the effectiveness of a wide variety of nail coatings that clients require to enhance and improve the quality of their nails.
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As a nail professional, you should consider the steps required to prepare the nail for a nail coating or artificial nail if etching into these upper layers is needed to allow the coating to bond. A brand that requires physical etching or buffing should be carefully considered as this will undermine the nail plate. Modern products do not require this method of bonding as technology has removed the need for these archaic methods.
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The developing nail in the matrix is very soft until full keratinisation has taken place and damage to this area can result in a permanently deformed nail. Examples can be seen in a person who has shut their finger in a door, even as a child. If the area of matrix is damaged, the base of the nail and the nail plate may have a permanent ridge. Another example would be if someone has had a serious infection in the area. If damage to the area if temporary and heals properly in the matrix, any deformity to the nail should grow out in approximately six months after the damage has healed.
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White spots in the nail plate are usually a sign of temporary damage to the matrix area, which results in the newly forming nail cells halting their full keratinisation process. The white spots are nail cells that have not fully keratinised and are still round and opaque instead of flat and clear. They will grow out. 
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More severe damage to the matrix can result in a permanent longitudinal ridge on the nail (from base to tip). This may be damage that will grow out but alternatively it could be permanent.
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Beaus Lines are horizontal lines on nail plates that occur due to a systemic condition that has effected the keratinisation process in the matrix. The normal formation of the nail plate has been altered but, after the systemic issues, it will return to normal, resulting in a ridge across the nail plate in the nail.
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Proximal nail fold or eponychium. The epidermis of the skin on the finger, above the matrix, folds back on itself and underneath. As in the hair follicle, the deeper area of the fold forms part of the germinal matrix and helps the area.
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This fold is living skin. The edge of the fold does not look like living skin because it is the epidermis folding back on itself and this does not have any nerves or blood vessels in it. It is often mistaken as the cuticle and non-living tissue! However, it is still living and, if cut, will react like any other area of cut skin and form a scar that will eventually thicken if cutting continues.
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This area of skin can often be quite large and unsightly, for example, when it is stuck to the cuticle, the nail grows and pulls the skin with it. When the skin is overstretched it splits, usually at the sides, and appears ragged. These splits can be quite sore and, if pulled, can become infected and inflamed. The split piece of skin can be very carefully removed with cuticle nippers. Proper care of the nails ensures that the nail fold does not stick to the nail plate as it is regularly lifted away. This area should not be pushed as this can cause damage to the underlying soft nail and matrix. The area also forms a seal around the proximal edge of the nail, which prevents bacteria from entering. When the nails are soaked in water or softened with oils, the nail fold can be lifted with ease. It is not recommended that the lifted skin is cut on a regular basis. The body is expert at protecting itself and, if an area is removed, the body will often compensate and grow thicker skin. The area should be treated with regular applications of oil or cream to keep the skin soft and prevent it from sticking to the cuticle. Applying nail oil everyday will cause this skin to shrink and the problem will disappear.
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Lateral nail fold or Side wall. The skin of the finger fold down along the side of the nail and provides the nail plate with protection and a groove to guide the growth of the nails. A seal is formed here to prevent the invasion of unwanted substances or microorganisms.
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Eponychium. The eponychium is an area at the base of the nail plate where the proximal nail fold meets the nail plate. It acts as a seal for that area of nail and guards against invasive bacteria. During a manicure, this area should be treatment gently because if the seal is broken, not only is it painful, but infection can occur.
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Perionychium. This is a term sometimes used in general for skin surrounding the whole of the nail.
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The cuticle. The nail fold is often called the cuticle, but this is inaccurate. The underside of the proximal nail fold constantly sheds a layer of dead skin cells that sits on the nail plate and grows with it. These calls are some of the stickiest in the whole body, which is why they stick to the nail and the eponychium sticks to them. This is the real cuticle and is not always visible until softened. This is the non-living skin that should be removed during a Manicure and always before the application of artificial nails to avoid any lifting problems, as products do not bond with the skin, only with the nail plate. As the epidermis of the nail fold produces this layer continuously, there is always some to be found on the nail plate, however little.
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The Nail Plate

The nail plate is created in the matrix. Modifications of skin cells become keratinised to form the hard, flat and transparent cells that make up around 100 layers of the nail plate. The plump, opaque cells gradually lose their cellular contents as the process of keratinisation takes place.
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Keratin
Keratin is made of proteins and all proteins are made from amino acids bonded together into strong chains. Protein chains contain between 5000 and 100,000 amino acids, much like pearls on a necklace. When equal thickness is compared, keratin proteins are actually stronger than steel! Amino acids are held together in their chains by covalent bonds - one of the strongest types of chemical bonding. In fact, without them, there would be no life on Earth; they're important.
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Keratin is further strengthened by sulphur cross-links, which are covalent bonds created between two separate protein chains. These cross-links join the chains together like rungs on a ladder. Cross-links can turn individual proteins chains in the nail plate into an ultra-tough , net-like structure. Cross-links also make the surface of the nail plate highly resistant to stains and the damaging effects of solvent's, cleaners, etc. The high level of cross-linking in nail and hair keratin is a primary source of their strength and durability. Nail plates contain many more cross-links and other types of bonds than hair, which helps to explain why they are so much tougher.
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Structure of the nail plate
There are areas within the layers of the nail plate. The top layer comes from the area of matrix that is furthest away from the free edge of the plate. These nail cells are harder and packed more compactly, making them more resistant to penetration and damage. This layer allows very little or no penetration of most substances into the nail plate, with the exception of those with a sufficiently small molecular size and a compatible composition. Unless both the size and composition are correct, no penetration will occur with healthy, intact nail plates. The few substances that do penetrate into the nail plate can't usually get past the upper 10 per cent of the nail plate's thickness, so these tend to collect and concentrate in the upper layers and may lead to discoloration. 
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Water is a small molecule with a composition that can penetrate more easily than any other substance known. But this also means it can escape more easily from the upper layers, which can alter the nail plate's shape and increase brittleness. There are certain types of natural oil, some of which are commonly used in nail oils, that have both the right molecular size and composition to penetrate into these upper layers. These can fill the tiny, natural voids between the layer and act as a lubricant. Flexibility reduced brittleness. Lubricants allow the layer to move against each other without any damage, thereby increasing flexibility. 
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Other substances with small molecules, such as some colourants, can concentrate within the upper layers and this can be seen as nail staining, e.g. some dyes or lakes used in nail polishes, nicotine from smoking cigarettes.
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The middle area of the nail plate grows from the centre of the matrix and its function is to make the nail flexible, which increases durability. The proper combination of strength and flexibility provides the property of toughness. Nail plates with the correct balance of these two properties will be more durable. Too much strength created a brittle nail plate, while too much flexibility creates a weak nail plate. This is why it is important to maintain the proper balance between strength and flexibility.
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The lowest area of the nail plate is the youngest and grows from the front section of the matrix. This is softer than the upper surface of the nail plate. This portion is in contact with the nail bed and helps to form the strong physical connection between the two by developing a series of grooves and ridges on both surfaces. These guide the plate as it grows towards the free edge. The nail bed also secretes moisture and oily substances that help keep the nail healthy and flexible. Some of these substances help to protect the nail plate from invasion by bacteria or fungal cells.
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The nail cells have a very orderly structure, rather like a brick wall. The keratinisation process produces two types of keratin: crystalline and non-crystalline.
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The crystalline keratin forms an interconnected mass of microfibrils (keratin fibres) that are arranged inside the nail calls. The fibre-like keratin rods lie neatly in rows that are parallel to the nail plate's free edge.
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The keratin microfibrils are embedded in non-crystalline keratin, which is a gel-like substance.
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These structures and others help to hold the nail cells together. These keratin fibres are arranged so that they lie across the width of the plate, which is important to help stop cracks from travelling from the free edge to the base of the plate (this would be painful and encourage infections). Damage to an area within the matrix can often result in a temporary or permanent groove running up the length of the plate. it is possible that the plate can split, following this groove where the plate is thinner.
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It is not possible for most substances to penetrate the nail plate and enter the bloodstream via the nail bed. Very few substances, other than water and the natural oil substances in the nail plate, can travel completely through the plate and emerge the other side.
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Water absorption
Everyone has experienced the effect of soaking nails in water (e.g. in the bath or a long soak during a Manicure). Soaking nail plates in water for longer than 60 seconds allows excessive amounts of water molecules to seep between the layers of nail cells, which causes swelling of the nail plate and shape changes occur. Excessive moisture also provides excess lubrication and allows the nail plate to bend easily and perhaps to crack and break.
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An excess of moisture makes the nail very soft and MUCH easier to damage. Any form of force on the surface of the nail can lead to surface damage. This includes buffing, which can lead to overly thin nail plates. Imagine using an abrasive on a piece of wood; it will cause little damage, just maybe smooth the surface slightly. Now imagine that same abrasive on a slab of butter: the surface will be disrupted and damaged and the soft butter will be dragged out of place. Soft nail plates must be treated with extreme care. The slightest surface damage will be seen as the nail as white spots. These white areas may appear to be dry, but in face, this has nothing to do with dehydration, nor is it an infection.
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Remember that 60 seconds soaking in water or any other solvent e.g. acetone, will make the surface softer and therefore more prone to developing surface damage for the next hour.
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As water and some other solvents are easily absorbed into the nail plate, the gaps between the layers will fill with water and swell. It is possible that this will break some of the bonds between the cells and cause internal weakening. It will also certainly change the shape of the nail plate. It is clear that applying a coating to a nail plate that isn't in its usual shape will cause problems with adhesion as soon as the plate returns to its normal shape. This is particularly evident with nail polish, as well as any other type of artificial coating's, e.g. UV gel or monomer and polymer system.
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As previously explained, keratinised skin cells form the nail plate. These flattened cells stick together and form layers. There are approximately 100 layers of keratinised skin cells (more in thicker toenails). There is less concentration of lipids (fats) in the nail plate compared to the stratum corneum (1 per cent versus 20 per cent) and there are many air spaces; this allows ten times as much water can be absorbed by the nail than by the skin. This can be seen when then nails are soaked in water, e.g. in the bath they become very transparent and flexible.
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Oil and moisture can travel through the nail plate in both directions. Secretions from the nail bed travels up from under the nail plate and help keep it flexible. Water and many other chemicals can travel down from the top of the nail plate as long as their chemical structure is small enough to work their way through the gaps created between the cells. Harsh chemicals such as detergents, bleach, etc. can strip away the oils and moisture from the upper layers and seep between the layers at the free edge where the bonds between the layers have broken. Nail oil on the other hand, when applied daily to the nail plate, can penetrate through the layers and fill up the spaces with a useful lubricant that will help keep the nail flexible and prevent unwanted chemicals from invading the nail plate.
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The bonds holding the cells together are tougher in the nail plate than in the stratum corneum, as the skin cells are designed to be shed, whereas the nail plate needs to be kept together.
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As the nail plate leaves the end of the finger, it forms a projection called the free edge. This appears whiter than the main body of the nail as it is not attached to the nail bed where light reflects off the coloured nail bed. The nail plate has a proximal and distal area and the free edge could be described as the distal edge. 
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Lunula. The lunula is also known as the half moon, an area of the nail by r under the proximal nail fold, and the front end of the matrix. It appears whiter because the cells are not yet completely keratinised, slightly plumper and not totally transparent. Not ever person has an exposed lunula and it is a misconception that the lunula (or half moon) should be visible. The nail is still slightly soft in this area and easily damaged so, if anything, it is better than the lunula is protected by the nail fold. People who have large exposed lunula often have very ridged nails, which is often more noticeable on thumbs. This is due to continual trauma to the soft nail from everyday living. During a Manicure or any work done in the cuticle area, care must be taken not to press too hard on the lunula, as it will cause a ridge on the nail that will need to grow up and off the end before it disappears.
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The nail bed. This lies directly under the nail plate. it is skin just like on the rest of the body and has many things in common with facial skin. It has a very rich supply of blood and lymph vessels in the dermis to keep the nail healthy. There are many different types of epidermis in the body and that which is in the nail bed closely resembles the lining of the mouth. The type on the nail bed is called bed epithelium. Tis is extremely sticky and it sticks very tightly to the underside of the nail plate. The dermis of the nail bed has a series of ridges from the lunula to the free edge. As the nail grows forward the bed epithelium separates from the dermis and slides along on these ridges like a railway track that keeps the train in place while allowing it to move. This is what holds the nail onto the nail bed. If the ridges are disturbed or if the nail plate becomes too thin and flexible, this hold is broken and causes the nail plate to separate from the nail bed. This is a dangerous situation as it allows bacteria in under the nail that could cause severe problems. Nail technicians must take extreme care not to over-buff the nail, as this will cause the nail to become too thin. If this thinning occurs anywhere on the nail, it will eventually grow up to the end of the nail bed where it is most likely to result in separation. Over buffing that causes heat acts like a friction burn on the nail bed and the bed epithelium will let go of the dermis, causing separation. The bed epithelium grows along with the nail and will appear under the free edge of the nail. This will slough off naturally or can be removed during a Manicure. This now useless part of the epidermis is sometimes referred to as the solehorn.
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The hyponychium. This is the area of the skin at the very end of the nail bed under the beginning of the free edge. It forms a very tight seal that prevents bacteria entering. There are many nerve endings in this area that act as a warning to this seal being broken.
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The onychodermal band. This is the area of the hyponychium where a slight change of colour in the skin can be seen. This is where the bed epithelium leaves the underlying dermis and is part of the seal protecting the nail bed from infection. When applying a French Manicure or artificial nails using a white-tip powder or gel, it is referred to as the smile line and its ideal shape should mirror the shape at the base of the nail to create a symmetrical top and bottom.
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Rates of growth
Like hair, nails grow at different rates in individuals and at different time of the year but, unlike hair, grow continually. Fingernails grow faster than toenails. As an average guide, nails grow at the rate of between 3mm per month and it takes approximately five to six months for a fingernail to grow from the matrix to the free edge and up to a year from a toenail. The growth rate is faster in the summer and during pregnancy and usually slows down with age. It can be speeded up or slowed down by illness. This slow growth rate complicates the treatment of nail conditions as damage caused to the nail plate takes a long time to grow out.
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The speed of strength of nail growth is not linked specifically to diet, vitamin or mineral intake but can be improved, along with the condition of the skin and hair, if a well-balanced diet is followed.
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It is quite common to be able to see the effects of systemic trauma on the nails. For example, a general anaesthetic, major emotional trauma, illness, etc. will often show up as a line or ridge on the nail plate where the growth has been affected.
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Technicians and their clients will often notice an increased growth rate immediately after artificial nails have been applied. This is due to the stimulation produced by buffing during application. The nail matrix and nail bed have a concentrated supply of blood and lymph vessels that supply the area with nutrients and remove waste products. Stimulation of the circulation in this area will improve this function and assist growth.
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Buffing the natural nail during a manicure is a valuable treatment, but care must be taken not to thin the nail or create too much heat through friction, as this can cause splitting.
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The effect of stimulation to the circulation can be seen in the general growth of nails: nails on the dominant hand grow faster, as does the forefinger. Nail biters have faster growing nails owing to the continual nibbling.
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As a technician, the growth rate of an individual's nail will affect maintenance treatments. Artificial nail must be maintained to compensate for this growth. The majority of clients will need to return every two to three weeks, but some clients need to return only four or five weeks, as their growth rate is slower.
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Nail composition and strength
Keratin and amino acids. The skin cells that are formulated in the matrix have, in their nucleus, the instructions needed to keratinise but, unlike the keratinised skin cells of the stratum corneum that form a barrier and then are lost, these cells form together to create the hard nail plate layers.
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As mentioned earlier, keratin is a type of protein that is made in the body and the body has many different proteins that are essential to its functioning. Proteins are made up of certain sequences of amino acids. Amino acids are chemicals created by the body that, when linked together in various specific sequences, make the necessary proteins. The linked amino acids form long strands and these strands are then linked together at intervals with hydrogen bonds, holding the strands together and creating a strong structure. The keratin of the nail has many more of these bonds than that of the skin and hair.
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Hard and soft nails. The progression of cells from the matrix to the nail plate is very similar to those making the journey in the epidermis if the skin. The cells are created by cell division deep in the matrix and, as they are pushed forward, lose the cellular fluid and become flatter. The lunula is an area where this process has not quite finished, hence its whiter appearance. As the cells are pushed forward by the reproducing cells behind, they become completely keratinised, flat and hard. Therefore the nail plate nearest to the nail fold is softer than the distal edge, and can be easily damaged.
  • A strong nail is one that can withstand breakage. This does not necessarily mean hard because hard could suggest brittleness and the nail could easily snap. Many products on the market are nail 'strengtheners', and that can mean nail 'hardeners'. If a weak nail is hardened too much, it will become brittle. If a hard n or brittle nail becomes too soft and flexible, it will tear. The spaces between keratinised cells are full of moisture from the nail ben beneath and from external sources. The right amount of moisture will keep the nail flexible and help absorb shocks. Too much and the nail bends, too little and the nail becomes dry and brittle.
  • The nail plate is very absorbent and too much water can cause splitting and peeling. Excessive water can cause the nail plate to soften and swell. Repeated softening and swelling can cause surface peeling.
  • The only truly effective moisturiser for skin and nails is water (and natural lipids), but in the right amount. Using creams and oils is beneficial as they can seal natural moisture in and keep too much out. Solvents, such as acetone and nail varnish removers, can remove natural oils and water and can be the cause of dryness if overused.
  • The perfect nail is a combination of strength and flexibility.
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A nail specialist should be able to diagnose the exact condition of a client's nail and be able to recommend the ideal treatment and products. It may be that a weak nail needs a hardening treatment for a period of time followed by a moisturising treatment. A brittle nail may need moisturising then hardening. An understanding of nail growth and structure brings with it the ability to correctly identify conditions.
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Protein, calcium and nails. As mentioned before, nails and keratinised skin cells. Keratin is a protein composed of amino acids formed together in long chains and linked by a hydrogen bond. The vast number of these strong bonds is specific to nails and is what makes them so much harder than skin and hair. The protein, keratin, is mostly composed of carbon, oxygen , nitrogen, sulphur and hydrogen. The nail plate also as traces of many other chemicals, e.g. iron, zinc, sodium, calcium, titanium, even aluminium, copper, gold and silver.
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There are many myths about calcium and nails. The body's intake and absorption of calcium is essential for teeth and bones, but as calcium is only 0.07 per cent of the nail (and most of this comes from external sources picked up by the fingers), it does not play a large part. The body needs vitamin D in order to absorb calcium and that is obtained from the sun and diet. If this vitamin is lacking, conditions such as rickets can occur. White spots on the nail are often blamed on a lack of calcium, but this is incorrect. They are usually caused by trauma to the matrix causing slight distortion of the cells or from surface damage. Calcium painted on the nail will not have any effect on the condition of the nail, neither will taking calcium supplements.
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The artificial nail and the natural nail. The strength of the nail can be influenced, even during the wearing of artificial nails or varnish. The nail plate is at its softest in the area of the lunula and there should be a narrow margin of nail that is not covered. A nourishing oil massaged into this area daily will effect the new nail growing, so weak or brittle nails can be improved while artificial nails are worn. The massaging will stimulate the area and the oil will help to reduce the moisture loss from the new nail. If the artificial nails are correctly maintained, the natural nails should be stronger when they are removed due to the protection of the overlay.
 
Can artificial nails damage natural nails? They certainly can if they are incorrectly applied or the wearer does not understand how to look after them properly. It is unusually an inexperienced or unprofessional technician or an uneducated client who causes damage to natural nails. It is really important that technicians explain what the wearer needs to do (or not do) in between treatments.

The Process of Nail Growth