The Skin, Moisturizers

Another basic skin care product that I can guarantee all of my readers have in their bathroom right now is a moisturizer. There are all sorts of moisturizers, from ones formulated for the body, the feet, the hands, your cuticles and face to the eye area. All of them work on the same principles, but they are formulated to provide the best performance in that particular body area.

Quick, go and check out the Epidermis Post again.

Why the body needs moisture
The body's "waterproofing" mostly consists of that lipid in between the cornified cells. There are quite a few different kinds of lipids in this layer including cholesterol (25%), free fatty acids (10-15%), ceramids (40%) and the rest is triglycerides, stearyl esters, and cholesterol sulfate. Some have suggested that the balance of all these particular lipids within the epidermis is very important for the function of the cells of the epidermis. All of these lipids are made by the cells of the epidermis as they move upwards through the epidermis, stored in the cells in little packets and then released out into the space between the cells. After release, a lot of the lipids are transformed through chemical reactions into slightly different lipids, and disruption of this process can harm the barrier function of the skin and lead to water loss.

Studies have shown though, that you can have all of the lipids in the world, but without a bit of moisture the skin loses its pliability, and becomes dry, hard and scaly. Within the epidermis (which is about 30% water), the water content is lower closer to the surface and about 1/3 of this water is within the lipid layer. The water is very important for the health of the epidermis, which needs to protect itself against water loss to the environment.


Types of Moisturizers
I've already mentioned some of these moisturizers with brief explanations in the past, but we'll go into what these are and their most common examples in more detail now.

Moisturizers basically help to trap, attract and redistribute moisture within the epidermis and most importantly within the cornified layer. By creating a temporary barrier, the skin below is allowed to take care of all this on its own. As this happens, the cells within the cornified layer and the layer itself will swell, creating the feeling of smoother skin.

Humectants
Humectants are great little things that attract moisture, helping to transfer water from the dermis into the epidermis. When the humidity is greater than 70-80% the humidity can even be pulled out of the air. However, there must be a balance, because humectants can also result in too much water loss from the dermis, into the epidermis and then out of the skin. When this happens, there is a feeling of tightness and dryness to the skin.

Humectants
Acetamide MEA Agarose Ammonium lactate Arginine PCA Betaine Butylenes glycol Cocamidopropyl Betaine Copper PCA Corn glycerides Diglycereth-7 malate Diglycerin Dimethyl imidazolidinone Erythritol Gelatin Glucose	Glucuronic acid GlucuronolactoneGlutamic acidGlycereth-12 Glycerin Honey extract Hylauronic acid Hydrololyzed wheat starch Hydroxyethyl sorbitol Lactamide Lactic acid Maltitol Melibiose Mineral oil Panthenol Pantolactone PCA Polyglucuronic acid Propylene glycerol	Saccharide hydrolysate Sea salt Seasame amino acids Sodium aspartate Sodium lactate Sodium malate Sodium PCA Sodium polyaspartate Sorbitol TEA-lactate Triglycereth-7 citrate Urea Xylose

Emollients
Emollients are very interesting moisturizers. They typically are water that has been mixed into a lipid, and the lipid can actually replace any areas of missing lipid within the cornified layer! As well, they provide an occlussive barrier, and allow the skin beneath to adjuct moisture levels on its own. The spreadability of an emollient often determines its application, whether it is an eye cream or a body cream for example.

Emollients
Acetylated lanolin Acetyl trihexyl citrate Avocado sterols Butyl myristate C 14-15 alcohols C 12-13 alkyl ethylhexonoate Caprylyl glycol Castor oil Cetyl acetate C 14-16 glycol palmitate C 12-20 isoparaffin Cyclomethicone Decyl oleate Diethylhexyl adipate Diethylhexyl malate Diisodecyl adipate Diisopropyl dilinoleate Dimethicone copolyol Dipropyl adipate	Ethylhexyl palmitate Ethyl linoleate Glyceryl dioleate Glyceryl ricinoleate Glyceryl stearates Glycol palmitate (palm oil) Glycine Soja (soybean oil) Glycol stearate Helianthus Annuus (sunflower) Seed oil Hexyl laurate Isocetyl alcohol Isodecyl steararate Isohexyl palmitate Isopropyl isostearate Isopropyl myristate Isopropyl palmitate Isosteryl alcohol Jojoba oil Lanolin	Methyl palmitate Myristyl propionate Octyl octanoate Octyl stearate PEG-4 lanolate PEG-5 tristearyl citrate PEG-7 Glyceryl Cocoate Polyglyceryl-6 oleate Plyclycerol-2 triisosterate PPG-20 cetyl ether PPG-4 laureth-2 Propylene glycol linoleate Squalene Sucrose oleate Sunflower seed oil glycerides Tall oil glycerides Tridycyl stearate Wheat germ glycerides

Occlusives
Occlusives may be the oldest form of moisturizer, and lanolin was one of the first used. Petrolatum is very commonly used today. Obviously, what they do is provide an occlusive barrier over the skin, helping the moisture within the skin to stay there and redistribute itself. Most occlusives also act as emolliants.

Occlusives
Acetylated Castor Oil Acetylated lanolin alcohol Behenyl isosterate Beeswax Canola oil Caprylic/capric triglyceride Carnauba Cetearyl methicone Cetyl ricinoleate Cholesteryl oleate Cyclomethicone Decyl myristate Dimethicone	Disteryl ether Glycol dioleate Hexyldecyl isostearate Hydrogenated castor oil Hydrogenated lanolin Isocetyl myristate Lanolin linoleate Lauryl Cocoate Lecithin Mineral oil- very frequently used due to it’s pleasant texture Myristyl myrisstate Neatsfool oil Octyldodecyl stearate Oleyl linoleate Palm kernal wax	Paraffin Petaerythrityl tetracocoate Petroleum Propylene glycol dioleate Shark liver oil Soybean lipid Stearyl stearate Squalane Tall oil Tocopherol Trihexyldecyl citrate Triisosterin Vegetable Oil

Other Ingredients
Obviously, in order to make a stable lotion ready for sale you need other ingredients.
Emulsifier: Helps to keep the ingredients mixed together well.
Preservatives: Again, we don't want bacteria to grow in our product.
Fragrance: This one should be obvious, but you should know that if you are sensitive to anything in a lotion, the fragrance is pretty high on the list of things for people to react to.

Things to avoid
If you have sensitive skin (meaning, you break out in a rash, not that you decided its sensitive) you might want to avoid these ingredients that are more likely to cause you problems.

Irritating Ingredients
Citral Cinnamic aldehyde Benzyl salicylate Phenylacetaldehyde Balsam of Peru Lemon oil Methyl heptane carbonate Methyl anisate Jasmine oil Cananga oil Ylang-ylang oil Balsam of tolu Bergamot oil Lavender oil Cedar wood oil Neroli oil	Petigrain oil Beeswax Spermaceti Essential oils Hexachlorophene Bithionol Parabens Almond oil Sesame oil Olive oil Corn oil Peach kernel oil Peanut oil Imidazolidinyl urea Sorbic acid Stearamido diethylamine	Triethanolamine Surfactants Vitamin E Sulfated alcohols Sodium lauryl sulphate Phenylmercuric acetate Alcohol or SD-alcohol followed by a number (Exceptions: Ingredients like cetyl alcohol or stearyl alcohol are thickening agents) Camphor Citrus juices and oils Eucalyptus Excessive fragrance Menthol Mint Peppermint Sodium lauryl sulfate

Using Moisturizers
It should be obvious to you by now that you should definitely be using a moisturizer, whether your facial skin is dry or oily, you likely need a moisturizer somewhere on your body. Keeping your skin moist helps with the skins suppleness, keeps you looking young, and most importantly maintains the barrier function of the skin.

Note that dry skin can not be helped by eating more oily foods or drinking more water (did you think it was selectively going to your skin?), and it can be made worse by bathing too often, using harsh soaps, and low humidity in the environment.

Notice that none of the above moisturizer types took moisture and just put it into each cell in your skin. Emollients have water mixed with them, which is the closest that you come! Moisturizers typically help with the water you already have in the skin, by creating a barrier and reducing water loss which then in turn allows water to relocate from the dermis and into the epidermis. So, the best way to get the most out of your moisturizer is to use it when you have the most water in your skin, which is right after cleaning! Try to seal in and keep any moisture in the skin by applying lotion less than 3 minutes after bathing (this is the time when the epidermal water loss is starting), so you can keep that moisture in the skin. Don't apply too often (remember that bit about humectants working against you and increasing water loss?), but in cases of very dry skin you might want to consider a very occlusive moisturizer that you use extremely often.

Note that your skin also does not enter a "reconstruction" or "healing" mode at night. The skin acts exactly the same while you are asleep as it did during the day. Therefore, you really don't need a different night cream. Having said that, your day cream should have sunscreen, but the night is a great time to take advantage of not being seen in public or having to wear makeup, so that's a great time to take advantage and have special ingredients in a thicker cream!

Product Reviews:
Bioelements Cremetherapy Mask
Olay Regenerist UV Defense Regenerating Lotion- SPF 15
Olay Deep Hydration Regenerating Cream
Bioelements Sleepwear
Skin MD Natural Moisturizer
Kiehl's Ultra Facial Moisturizer
Kiehl's Light Nourishing Eye Cream
Kiehl's Ultimate Strength Hand Salve
Become Age Resistant Rejuvenating Hand Cream
Olay Regenerist Micro-Sculpting Cream
Gloves in a Bottle

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The Skin, Peptides

Go back and read through the Dermis Post again. Just go glance at it quickly, I won't get too terribly technical with you, I promise! If you want more info, check out the reference paper below. It's a great overview of Peptides and what they have been found to do.

Ok, well, remember those cells I said were present in the dermis? The fibroblasts? Their job is to create collagen, a major component of the matrix of extracellular things in the skin. (My husband, an expert in the Extracellular Matrix is going to kill me for simplifying everything so much. His grad students would laugh at me. But, this isn't a PhD Disseration, it's a beauty blog!) One of the major problems with aging (both from age and from sun exposure) is that the skin's collagen is made is smaller amounts, what is there is broken down more quickly and the fibroblasts themselves replicate more slowly as they die off. This happens more quickly in photoaged skin than just aged skin, so the results of decreased collagen are even more pronounced.

Where do peptides come in? There is a lot of evidence that peptides can do a lot of things to help overcome this issue. Not only do peptides stimulate fibroblasts to replicate, they stimulate production of collagen and even help to inhibit it's breakdown! Peptides can even be used as couriers, bringing in beneficial things such as copper (which is very vital to wound healing, copper also helps to stabilize the collagen that is present). Now, these studies have all been done with very specific peptides, and most products don't tell you exactly which peptides are included, but there is real evidence out there that peptides work!


Reference: Lupo, MP. Cosmeceutical Peptides. Dermatol Surg. 2005;31:832-836

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The Skin, Cleansers

The first group of products that we'll review will be cleansers. If you use nothing else on your skin, I know you do use a cleanser! There is a huge array of products out on the market, with many different price points, different additives and different formulations.

Quick, read the epidermis post if you haven't yet (or re-read it if you have, I added a few things) before we start!


How Soap Works

All cleansers work the same way, whether a $1 bar of soap or a $100 bottle of La Mer cleanser. Really! In order to both get rid of oils, sweat and dirt on the skin while making the whole thing water soluble, surfactants are used. Basically, look at the left side of the picture above. This is the basic soap molecule. There is a long chain of non-polar (neutral) atoms (that part that looks like a tail) and this part is attracted to the dirt, oil, etc. The other end (the polar, or charged end) is attracted to water. So, lots of little soap molecules will surround the piece of dirt, oil or whatever; see the right side of the picture. Note how they surround the offensive bit with their non-polar end, and the polar (water attracting) end is out into the water, allowing the whole thing to be water soluble.

Note that not all cleansers are technically "soap." There are soaps and detergents, the difference is the way in which they are made, in addition to their pH. Soaps tend to be more alkaline, and as such may result in more drying and irritation of the skin. Both work through the surfactant mechanism I just described, and there are different fats and additives that compose the rest of the cleaners.

The whole thing sounds pretty simple, doesn't it? Well, there are definite downsides to this whole process.

1. Redness and Irritation: The soap molecules may surround and damage the Keratin within the skin. This allows the Keratin to swell and become overhydrated, damaging the skin and it's barrier function. In turn, this allows the soap to penetrate more deeply into the skin, where they interact with nerve endings and are attacked by the body's immune system, resulting in irritation, redness and itching.
2. Dryness: The soap molecules may remove some of the lipid between the cells of the Cornified Layer, and may also remove some of the moisturizing molecules within the cells of this layer as well.
3. Tightness after Washing

The extent to which a soap is irritating depends upon several thing- the potency of the surfactant, the pH of the soap (higher pH=more basic/alkaline=more irritating, irritating soaps will be in the range of 9.5-11), and rinsability. All of these effects are minimized by adding moisture through depositing lipids and humectants (things that attract moisture) into the skin. As well, artificially created surfactants (also called syndets) are less harsh on the skin than more naturally created surfactants.


Types of Cleansers

There are many fomulations of cleansers out of the market today, and often the only way to discover what type of cleanser you have is to check the label!

Most soaps can be easily divided in terms of their composition, I find this the easiest way to think of them.
1. Soap: Old fashioned soap, pH is usually 9-10
2. Combars: Combines soap with "surface active agents" with a pH 9-10
3. Syndet: Synthetic detergents rather than than mostly soap surfactants, they usually are <10% soap, and have a pH of 5-5.5 which means they are often more gentle on your skin.

Soaps are also commonly divided by how they are made, especially those that are in bars. I'm not going into the whole process or explanation, but you can read a pretty decent explanation of it here on Wikipedia.


Considerations for Certain Forms of Cleansers
1. Liquid: When liquid soaps first came out, they were quite the revolution in the cleansing industry. Their formulas allow milder surfactants and more (and better quality) moisturizers to be used.
--Emollient-Rich vs. Humectant-Rich: Both are forms of moisturizers, however humectants simply attract moisture to the epidermis, and are easily washed off of the skin. Emollients help to fill in the spaces between the corneocytes in the cornified layer, and as they are not water soluble, they are not easily washed away. Emollient rich body washes are made by Dove and Olay.
2. Bar: Bar soaps are typically more aggressive in terms of their surfactants. This means that not only will they do a better job of removing soap and oils, they also will be more likely to irritate and dry out the skin.
3. Lipid free cleansers: A liquid cleanser that cleans without fats, it removes dirt and makeup easily and leaves behind a thin film. Often used by those with sensitive skin.
Usually contains: water, glycerin, cetyl alcohol, stearyl alcohol, sodium laurel sulfate (a detergent), and propylene glycol (can cause stinting).
4. Cleansing Creams/Cold Creams: They seem old fashioned I know, but they are pretty great for dry skin. Usually contain water, mineral oil, petrolatum, and waxes, they use a borax derived detergent (decahydrate of sodium tetraborate)
5. Body Washes: Depends upon a little plastic poof to add water and air to disperse the product (you know the one I mean, it's hanging in your shower right now), they are made of synthetic detergents (therefore less harsh on the skin) and they can have high amounts of petrolatum for hydration (Oil of Olay's body wash has 17%, I heard from a dermatologist that this is the highest % on the market).
6. Low-foaming Washes: Often used to wash the face, often they have little to no surfactant, but do not contain moisturizers such as humectants or emollients. Cetaphil fits into this category.


Common Cleanser Ingredients
Pretty much all surfactants are made from an oil/fat which reacts with a base, producing the surfactant molecules you saw in the pic above. The length of the carbon chain "tail" depends upon which oil you started with, for example those with 10-14 carbons in the chain are more aggressive and more irritating (these are mostly derived from coco oil).

How to read an Ingredients list at The Beauty Brains

Purpose	Ingredient
Surfactants	Natural soap	synthetic surfactants
Preservative/Antioxidants	(BHT) butyl hydroxy toluene	2-t-butylbenzene-1
Detergents	sodium cocoate sodium tallowate sodium palm kernelate sodium stearate sodium palmitate triethanolamine stearate sodium cocoyl isethionate sodium isethionate	sodium dodecyl benzene sulfonate sodium cocoglyceryl ether sulfonate sodium laureth sulfate- a harsher surfactant cocoamido propyl betaine lauric acid diethenolamine (lauramide DEA), sodium cocoyl isethionate disodium laureth sulfosuccinate Decahydrate of sodium tetraborate Ammonium Lauryl (or Laureth) Sulfate - a milder surfactant
Preservative/Sequestering agent (keep hard minerals in the water)	(EDTA) ethylene diamine tetraacetic acid (EHDP) hydroxyethane diphosphonic acid, also known as editronic acid	Complex phosphates and sodium citrate
Whitening agent	Titanium dioxide
Processing aids	Salt
Fillers	Starch, clays, salts, etc.
Lather Boosters	Co-surfactants (e.g., SLES and betaine)	sodium carboxymethylcellulose
Antibacterial Agents	Benzoyl Peroxide Sulfur	Resorcinol antibacterials --triclocarban- attacks gram + bacteria --triclosan- attacks gram + and - bacteria
Moisturizers/Skin Feel Agents	Polyols Glycerin	lanolin petrolatum
Humectant-Attract water from the dermis into the epidermis, and from the air in humidity >70%	Acetamide MEA Agarose Ammonium lactate Arginine PCA Betaine Butylenes glycol Cocamidopropyl Betaine Copper PCA Corn glycerides Diglycereth-7 malate Diglycerin Dimethyl imidazolidinone Erythritol Gelatin Glucose Glucuronic acid Glucuronolactone Glutamic acid Glycereth-12 Glycerin Honey extract Hylauronic acid Hydrololyzed wheat starch Hydroxyethyl sorbitol Lactamide Lactic acid Maltitol	Melibiose Mineral oil Panthenol Pantolactone PCA Polyglucuronic acid Propylene glycerol Saccharide hydrolysate Sea salt Seasame amino acids Sodium aspartate Sodium lactate Sodium malate Sodium PCA Sodium polyaspartate Sorbitol TEA-lactate Triglycereth-7 citrate Urea Xylose
Emollient	Emollients help to fill in the spaces between the corneocytes in the cornified layer, they remain in the layer Acetylated lanolin Acetyl trihexyl citrate Avocado sterols Butyl myristate C 14-15 alcohols C 12-13 alkyl ethylhexonoate Caprylyl glycol Castor oil Cetyl acetate C 14-16 glycol palmitate C 12-20 isoparaffin Cyclomethicone Decyl oleate Diethylhexyl adipate Diethylhexyl malate Diisodecyl adipate Diisopropyl dilinoleate Dimethicone copolyol Dipropyl adipate Ethylhexyl palmitate Ethyl linoleate Glyceryl dioleate Glyceryl ricinoleate Glyceryl stearates Glycol palmitate (palm oil) Glycine Soja (soybean oil) Glycol stearate	Helianthus Annuus (sunflower) Seed oil Hexyl laurate Isocetyl alcohol Isodecyl steararate Isohexyl palmitate Isopropyl isostearate Isopropyl myristate Isopropyl palmitate Isosteryl alcohol Jojoba oil Lanolin Methyl palmitate Myristyl propionate Octyl octanoate Octyl stearate PEG-4 lanolate PEG-5 tristearyl citrate Polyglyceryl-6 oleate Plyclycerol-2 triisosterate PPG-20 cetyl ether PPG-4 laureth-2 Propylene glycol linoleate Squalene Sucrose oleate Sunflower seed oil glycerides Tall oil glycerides Tridycyl stearate Wheat germ glycerides
Occlusives-Greasy ingredients that help to slow the evaporation of water from the skin, they are most effective when applied to damp skin	Acetylated Castor Oil Acetylated lanolin alcohol Behenyl isosterate Beeswax Canola oil Caprylic/capric triglyceride Carnauba Cetearyl methicone Cetyl ricinoleate Cholesteryl oleate CyclomethiconeDecyl myristate Dimethicone Disteryl ether Glycol dioleate Hexyldecyl isostearate Hydrogenated castor oil Hydrogenated lanolin Isocetyl myristate Lanolin linoleate Lauryl Cocoate Lecithin	Mineral oil- very frequently used due to it’s pleasant texture Myristyl myrisstate Neatsfool oil Octyldodecyl stearate Oleyl linoleate Palm kernal wax Paraffin Petaerythrityl tetracocoate Petroleum Propylene glycol dioleate Shark liver oil Soybean lipid Stearyl stearate Squalane Tall oil Tocopherol Trihexyldecyl citrate Triisosterin Vegetable Oil

Surfactant Picture
Bar Soap Picture

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The Skin, Subcutaneous Tissue

The subcutaneous tissue is the last of our skin layers to review. This layer contains a lot of blood vessels and nerves, and provides a lot of support to the skin above. This layer is made up primarily of fat lobules, held together with Collagen bundles. Basically, this is where you get a lot of your shots, and although technically this is a layer of fat underneath the skin itself, this layer is extremely important to the look of your skin. Too little (think of an aging face) and things start to appear sunken and the skin is loose. There really isn't too much else to say about the Subcut.

Next in our series, we'll review basic skin care before heading into the specific targeted products that we all use!

Today's Image

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The Skin, Dermis

Directly beneath the epidermis is the dermis, and it functions primarily to support the epidermis. As well, the dermis supplies the epidermis with things that are important, such as, oh, blood! The dermis does vary in thickness depending upon the area of the body just like the epidermis. Overall, there are fewer cells within the dermis, this layer is composed of many more structural components such as collagen.

Technically, there are layers, however this is less of structured tissue than the epidermis:
1. Papillary Layer- This layer is thinner and more superficial. It has all 3 tissue types, but is loosely packed. This layer also contains capillaries, which are small blood vessels and they are primarily supplying the epidermis and dermis.
2. Reticular Layer- A deeper layer, this is more densely packed, the blood vessels here are larger, and the tissues are just larger in general.

Both of these layers are made up of several tissue types and other components:
1. Collagen- Think of collagen as a rigid structural component of the dermis, really helping to support the skin. The dermis is about 85% Collagen, and these long proteins will link together to provide even more support. There are several types of collagen, we won't get into that here.
2. Elastic Tissue- Less than 1% of the dermis, but these fibers really do what it sounds like they do- they help the dermis "snap" back into shape.
3. Reticular Fibers
4. Cells- There are two main types of cells:
a. Fibroblast- These cells create collagen and elastin, and they can be stimulated to do so!
b. Macrophage- These are the scavengers of the skin, they are part of the immune system.
5. Ground Substance- I tend to think of all the cells and tissues (the collagen, elastic and reticular fibers) as sitting in a jello-like substance, this is the ground substance. The things that make up the ground substance are made by the fibroblasts and consists of mucopolysaccharides (primarily hyaluronic acid), chondroitin sulfates, and glycoprotein. Notice that some of those things probably sound familiar, especially hyaluronic acid. These are bigger proteins, and they are way too big to be moving between layers of the skin. This means that you can't put them on the surface of the skin and expect them to get down to this layer, where they'll do some good! But, when they're here in the dermis, they help the skin hold its structure.

Special Structures found within the dermis:
1. Oil (sebaceous) Glands
2. Scent (apocrine) Glands
3. Eccrine (sweat) Glands
4. Hair- We will discuss hair much more in detail later in the series
5. Nerves, Touch and Pressure sensors




Today's Image

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The Skin, Epidermis

The epidermis is our outermost layer of skin, and can vary in thickness from 0.05 mm (eyelids) to over 1.5 mm (soles of the feet). There are no blood vessels within the epidermis, and the openings to hair follicles, sweat and oil glands are in the epidermis (the rest of these specialized units are within the dermis).

The Layers of the Epidermis
The epidermis is separated from the dermis by a basement membrane, but this does keep the two firmly attached. Since we lose so many skin cells each day, our body must constantly create new cells as replacements. Cells start at the bottom layer and work their way up to the surface as they mature.

1. Basal Layer (stratum basale)- the bottom layer, these are the cells that are dividing to replace the cells that are lost every day.
2. Spiny Layer (stratum spinosum)-These cells begin to create fats known as Sphingolipids and proteins known as keratins (for strength). They are called spiny because while all of the cells in the epidermis are connected to each other very tightly with little bridges called desmosomes, the desmosomes are really easy to see in this layer, and under the microscope all of these cells look like they are covered in spines.
3. Granular Layer (stratum granulosum)-The sphingolipids begin to clump together, giving these cells a granular appearance under the microscope. By the time these cells reach the top (cornified layer) they will die and release all of this lipid into the surrounding area. The lipid then will work almost like mortar to keep the cornified cells together and keep water in the skin.
4. Clear Layer (stratum lucidum)- This layer is primarily dead cells, filled with the lipid that has not yet been released. This is the layer that is the biggest provider of the skin's barrier function and is waterproof.
5. Cornified Layer (stratum corneum)- The top layer, these fibrous cells are (still) dead and will shed roughly every 2 weeks. The cells are little more than a cell membrane surrounding Keratin and other structural proteins. there is a moisturizing molecule in the cell, more on that below. This layer is very tough, and provides most of the protection of the skin. Though pictured here as pretty thin, this layer is usually 15-100 cells deep and they are very tightly bound with the lipid in between them like brick and mortar on a building.
Think of the cells here as bricks, held together by the desmosomes as in the layers below, but also in part by the lipids (fats) that are between the cells. These are the lipids released by the granular layer and clear layer (#4 and 5). Because oil and water don't mix, in between the lipids there are droplets of water basically, all clumped together. They aren't able to absorb down because the lipids are in the way, they are basically stuck there.
Within the cells themselves there are molecules that absorb water from the environment (water, air, etc), and then hold them here to be used in the lipid layer. Note that these molecules are water soluble, so they can be basically sucked out of the skin by water in the environment as well (eg- when swimming), which means that with repeated exposure to water you can become more dehydrated.

The Special Cells of the Epidermis
1. Melanocytes- these cells are nestled between the cells of the Stratum Basale, where they produce melanin. Melanin helps to absorb sunlight, protecting the skin from the harm of UV radiation. The melanin is packaged up into little packets (melanosomes), and then given over to the surrounding cells. The number of melanosomes in each race and skin tone is the same, what differs really is just the size of these little melanosomes. The melanin in them is the same. Really. Melanin is increased by several hormones, and with age the melanocytes themselves die off.
2. Langerhans- These cells come from the bone marrow and are found throughout the epidermis, they have function within the immune system, particularly for contact hypersensitivity rashes.
3. Merkels- These cells are found only in certain areas (nailbed, ends of fingers, etc) and they are involved in light touch perception.


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The Skin, Introduction

At long last, here it is, the beginning of my series on the skin! I've pulled together info from lots of different sources for this series, so it has taken a while. As well, since I didn't want to intrude on anyone's Copyrights, I started to draw my own pictures using pencils, markers and even crayons! Then, this was taking so incredibly long, I found some copyright free images from Wikipedia, so things have sped up somewhat.

Please remember that I am not a Dermatologist, I am a Pediatrician! Also, somewhat more important, I am not your doctor!

So, this series is meant for just general information, to better educate all of us about the skin's purpose and function. It is easier to research problems and products for our own skin when we have a basic understanding of what is happening and why this works. As well, you'll then be able to know that someone is giving you a line when they say that pores can open and close, because you'll know that this is anatomically not possible!

I've divided this project up into lots of parts, to make everything more digestible.
Part 1- Anatomy & Function: A basic overview of skin anatomy, and then separate posts going into each of the layers and parts, with discussion of the function of each of these parts
a) The Epidermis
b) The Dermis
c) The Subcutaneous Fat Layer
d) Sweat Glands/Pores
e) Hair Follicles
f) Nails

Part 2- Effects of Lotion & Cosmetics
a) Sunscreen
b) Retinoids
c) Peptides
d) Antioxidants
e) Hydroxy Acids

And a huge list of other posts that I have started to pull together, so many that I can't even mention them all here. However, I've started researching them, and there are so far about 20 or so posts in this series, and I'm sure that it will grow even more.

Resources that I've used to pull this series include (but this is certainly not a comprehensive list):
-Netter's Atlas of Anatomy
-Habif, Clinical Dermatology
-Fitzpatrick, Color atlas and Synopsis of Clinical Dermatology
-Clinics in Dermatology
-And of course my husband, who shall remain nameless. He is a Biomedical Engineering professor with a lab that focuses on extracellular architecture and interactions, including research on Melanoma (so, he's very familar with the skin and all this stuff!)
-Today's skin image

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