The Basic Structure of Skin, Hair, and Nails

The Basic Structure of Skin, Hair, and Nails

January 05, 2021

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The skin is a complex organ that plays a number of roles.  Although many think of it through just a cosmetic lens, the reality is that our skin is playing a number of vital functions for our overall well being. When I counsel my patients on taking care of their skin, it’s not just about how it looks. Understanding the skin and its roles will help you understand why we need to care for it.

 

Only in the past couple of centuries has the skin really been understood to be a complex organ.  Prior to that it was viewed as a tarp or container and often looked at as an affliction when something went wrong.  Think of the plagues and how visual the descriptions of the skin were!

 

Advances in Dermatology have shown this to be far from the truth.   We now know the skin serves an essential role to communicate between your body and the environment around you.



The skin serves many functions.

 

  1. Protection.  The first role our skin plays is protecting our body from the environment. Think allergens, infectious agents such as bacteria, yeast, fungi, viruses, pollutants…
  2. Sensory organ.  There are sensory receptors located in varying concentrations throughout our skin. These allow you to feel a pin prick, vibration, pressure…  Your skin is in communication with your nervous system to convey these sensory messages.
  3. Climate control.  By controlling the local flow of blood to your skin by constricting or dilating your blood vessels, your skin can help your body regulate its heat balance.  If it is a little too hot, it even has the ability to produce sweat so this can evaporate and cool the skin further.
  4. Manufacturing.  Your skin is busy producing Vitamin D for your body by its interaction with UV. 
  5. Immune system.  I often explain our skin as almost like having its own immune system that interacts with our internal immune system but in many ways has a role of its own.  By interacting with pathogens and allergens it can play a role as your first line of defense. 
  6. Excretion.  Our skin can help get rid of wastes and toxins in the body.
  7. Fluid Balance.  Through sweating, our skin can play a role in reducing our water load.  

 

Next, we will focus on learning about the actual building blocks of the skin.

 

 

Did you know just how many functions our skin is designed to perform?

 

In many ways, the cell layers that make up the skin are like bricks in a brick wall or stones that make up a cobblestone street.  

 

The basic layers of the skin are 3: 

  • the epidermis
  • the dermis
  • the adipose or fat layer. 

 

Epidermis 



Think of the epidermis as the layer of skin you see directly.  More specifically, this part of the skin is composed of 5 layers of cells progressing from the basal layer to the stratum corneum.  These cells are called keratinocytes and form a barrier to the environment.  

 

Keratinocytes have many functions.  They are responsible for producing vitamin D for the body and converting it into its active form.  They also produce a protein called keratin.  If you have ever had a whitehead or blackhead or cyst and squeezed it and found cheesy white stuff that came out - that is keratin.  It can have a bit of an odor if bacteria are present. This keratin actually plays a role in forming an effective barrier from the environment and preventing pathogens from getting through the skin. 

 

Melanocytes are of neural origin and are the cells responsible for producing pigment in the skin.  They have dendrites or long arm extensions that connect to keratinocytes to provide these cells with melanin. 

 

Langerhans cells are found in the epidermis and are thought to be a type of immune cell that may function somewhat like a "watchman".  It is looking for outside pathogens and informs the immune system in case a reaction needs to be mounted.  

 

Lymphocytes are also immune cells in the skin working to protect our body from environmental insults.

 

Merkel cells are found at the base of the epidermis and have a close connection to the nervous system.  They are thought to play a role in sensation to sense touch.

 

 Each of these cells has the ability to misbehave and form different types of skin cancer as well. 

 

Cell Type Potential cancer that could arise from this cell type

Keratinocytes

Squamous Cell Carcinoma

Keratinocytes

(in the basal layer of the epidermis)
Basal Cell Carcinoma

Melanocytes

Melanoma

Lymphocytes

Cutaneous Lymphoma

Merkel cells

Merkel Cell Carcinoma

 

 


Dermis



The next layer is the dermis. This is where we find blood vessels that nourish the skin and play a role in thermoregulation.  It is also where collagen and hyaluronic acid are found.  This is the support that provides the structure for the skin.  We find many structures in the dermis. 

 

The dermis is where we find hair follicles, sweat, glands, sebaceous glands, blood vessels, nerves, and lymphatic vessels.  If you nick yourself and bleed, then you have gone past the epidermis into the dermis since there are no blood vessels in the epidermis itself.  This can give a good sense of just how thin the epidermis can be while the dermis can be much thicker.  

 

Fibroblasts are found in the dermis and are responsible for producing connective tissue and assisting in healing after injury to the skin.

 

Capillaries are found through the dermis to provide blood flow and nourish the skin.  Lymphatic vessels are also found that remove waste and excess fluid.  When our cheeks look flush with redness, this is because the capillaries have vasodilated to give an overall red appearance to the skin.  

 

It is interesting to note that collagen is found in the dermis, below the epidermis.  Although some products will boast about collagen as an ingredient, it is not necessarily true that collagen can be applied superficially to the skin and find its way into the dermis.  Although there may be some overall improvement in the appearance of the skin, this is likely from excess hydration in the superficial layers of skin from the product.  

 

Eccrine glands are located in the dermis.  They produce sweat and drain directly to the skin.  These glands are found throughout the skin from head to toe with a higher concentration on the palms and soles.  The sweat produced has no odor and is composed mostly of water.

 

Apocrine glands are also located in the dermis but secrete into the pores where hair follicles are found. The sweat produced by the apocrine glands is a bit different in that it is oily and can have an odor once bacteria act on it.  These glands are located in specific areas such as the underarms, eyelids, nipples, ears, perianal area, outer edges of the nose, and external genitalia.  

 



Sebaceous glands secrete an oily wax-like substance into the hair follicle to provide moisture and lubrication to the skin and hair.  These glands are found predominantly in the scalp, face, and upper torso.  There are some areas where they can concentrate such as the lips, nipples, and groin.  

 

 

 

Fat

 

Below the dermis is the fat or adipose tissue.  This layer is not just about insulation.  It plays a role in wound healing and possible hormonal links as well. 

 

Special Note on Mucosal Skin

 

Mucosal skin is thinner and tends to line the digestive tract, reproductive tract, and respiratory organs.  It tends to be moist and some mucosal skin can secrete mucus to lubricate the skin further. When it comes to transitioning from keratinized skin to mucosal (or non keratinized) skin, the key factors that define the mucosal skin are that it tends to be thinner has a pink or purple hue and it tends to be moist.  

The labia majora, the outer part of the labia, is considered keratinized skin.  The skin lining the labia minora is mucosal skin.  This is the area that is just internal to the labia majora and surrounds the vagina. 


 



The bioflora, the mix of bacteria and yeast, regulate the pH of the vagina very effectively.  This delicate balance can be negatively impacted by attempts to use specialized washes.  These washes run the risk of altering the pH in such as way that irritation can develop.

Hair

 

Hair - too little, too much, too dry, too oily, too gray, shedding -- there are so many challenges!

 

Each of these concerns will be addressed in different posts since each is a topic in and of itself.  Before understanding each topic, however, there are some hair basics that need to be covered first to lay the groundwork.  By understanding these facts, understanding hair products, hair promises, hair damage, and hair loss will come into better perspective.  

 

The first basic fact to get on the table: the hair and the scalp are two different things.  

 



Think of your scalp like a farm. To continue the analogy, the scalp is the soil that grows a crop called hair. If the scalp is not healthy then the hair that grows from it cannot be either. If there is inflammation, itching, and/or irritation think of these issues as complications that can impact the way that your hair grows. It can make your hair grow out fine and wispy, or it can grow out damaged and easily breakable. Or, once those hairs grow they can actually be damaged by trauma from your fingernails.


 



Your hair is rooted deep in the dermis when it is actively growing. For this reason, you cannot easily pull out actively growing hair. 

 

What does “actively growing” mean? 

 

There are three eases to the lifecycle of a hair follicle. There is the growth phase, a transitional phase, and a resting phase. The names for each of these cycles are anagen, catagen, and telogen, respectively.  

 

When hair is in the anagen or actively growing phase, it is deeply rooted in the dermis of the skin. For this reason, these hairs cannot be easily pulled out or removed. Many of my patients suffering from hair loss will comment that they avoid washing their hair out a fear that their hair will come out easily. The reality is that the hairs that do fall out easily are not actively growing - these are telogen hairs that have already entered the resting phase.   

 

The hair follicle may likely already be transitioning into a new growth cycle. In many ways, it does not make much of a difference whether or not the hair is washed because these hairs would inevitably fall out. Think of the hairs that come out of these follicles as likely making way for a new hair follicle entering into the antigen or growth phase. The challenge with this period of time is that the new hair growing in will be fine, peach fuzz like a ‘baby’ hair. 

 

Hair grows like a blade of grass it starts off tapered at the end and gets wider as it gets longer. It takes time for this to happen. Unfortunately, it can be a frustrating period of time because watching hair grow is like watching water boil or grass grow. It takes a while. 

 

Normally most of our hair is in the growth phase with a cycle across our scalp happening randomly with hairs entering the resting and then re-entering the growth phase again. 

 

At the base of every hair follicle is an oil gland. This oil or sebaceous gland is secreting oil that migrates down the shaft of the hair follicle. It takes about a day for this oil to migrate about an inch from the scalp. When we wash her hair, we are removing this oil. For people with short hair, it can only take a day or two to ‘re-grease’ the hair that they have. Those with longer hair will find that it can take a few days if not longer to really feel like the hair has its oil back. In a future post, we will discuss hair products and the impact they have here.

 



Another thing to consider is the actual structure of the hair shaft itself. The surface of a hair follicle is actually not smooth, it is scaly. This plays a significant role in considering how hair products and hair color at work by lodging within the scale of these follicles. When you transect the hair follicle, the shape that you find actually can dictate if your hair is curly, straight, wavy, etc.

 

Lastly, hair color is dictated by the amount of melanin in the hair follicle itself. This melanin is produced in the cortex of the hair and moves down the shaft. The type and amount of melanin can dictate the actual pigment of the hair.



Nails 

 

Although nails are often considered cosmetic, the reality is that they can be a reflection of our health.  Learning about normal healthy nails is a good starting point.

Related: Nails : Does the color reflect your health?

 

The key thing to remember about nails is that the nail plate itself is composed of a hardened protein called keratin. The pink hue that we see associated with a healthy nail plate is actually a window to the hue of the nail bed underneath and its vasculature.

 

The whitish half-moon base of the nail plate is the visible part of the nail matrix. The amount of this visible can vary widely depending on where your cuticle ends.  Some people may believe that the cuticle should be pushed back to reveal this half-moon.  The reality is that doing so can often cause more damage to the overall health of the nail plate itself.

The next part of the nail is the pinkish area that overlies the nail bed. This is followed by the free edge of the nail plate will appear whitish as it is just the keratin itself with no underlying skin so you can see how it is somewhat translucent.















A nice healthy nail will have a pinkish or mauve hue as it reflects the color of the nail bed underneath. When you apply pressure to this area, you should be able to make this color disappear temporarily and reappear rapidly once pressure is released. This is a sign that you are well hydrated and have good blood flow to your tissues! By applying pressure you are pushing blood away from the tissues and then releasing pressure allows it to flow back in.  This is referred to as the capillary nail refill test. If you cannot quite get a good glimpse of this, try using a drinking glass to apply gentle pressure and then release.  This way you can witness the pale hue quickly turn pink once the blood flow returns.



Related : Nail Biting, also known as onychophagia



The most important advice I have for my patients to maintain healthy nail growth is to protect their cuticles! This is the skin around your nails.

Remember the nail plate is just keratin that grows out of the nail matrix. The cuticle is the skin right on top of the nail matrix. Protecting your cuticle will protect your nail growth.  The cuticles serve as a barrier to protect your matrix from bacteria, fungus, yeast, inflammation, and trauma.



Many people are shocked to hear this but I do not recommend cutting or removing your cuticles. Once you do this, you open your nail matrix up to not only infections but other problems such as grooves and irregularities in the nail growth. 

 




There is a myth that pushing your cuticles back will make your nails grow faster. Pushing them back just gives the appearance of longer nails for cosmetic purposes. It’s ok to gently push this skin back if this is what you are trying to achieve- there’s just no need to cut it!



Keeping your skin well moisturized, especially around the nails and especially in the winter when we are all prone to dry cracked hands, will help keep your cuticles healthy and support healthy nail growth.

Applying petroleum jelly to your cuticles every night will help keep them hydrated. Any thick moisturizer can serve the same purpose.

 

Related: Does the texture of your nails reflect your health?

 

One of the most important pieces of advice I have for people that get manicures is to speak up if your manicurist is particularly aggressive with your cuticles!  The damaging effects will take months to recover from as most fingernails take 3-6 months to grow out while toenails can take as long as 6-12 months to grow out.




Remember, nails are not just cosmetic. Often they can cause a lot of practical problems for people- getting caught on clothing, soreness, pulling back on socks and shoes.





Nail health is important because if we do not address these issues early on, the damage to the main matrix can result in permanent nail damage. The most common nail concern tends to be nail fungus. Even though we have some treatments for this, many people do not realize that if the fungus damages your nail matrix, even if you treat the fungus the nail may stay permanently thickened and difficult to manage.



 

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