Skin Care Dictionary and Vocabulary

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Definitions for STS web site library

Skin Anatomy:

Skin Barrier

The skin barrier is located in the stratum corneum, which is the uppermost layer of the epidermis. It is comprised of a lipid bilayer, which retains moisture and prevents allergens and irritants from entering the skin. When the skin barrier is damaged, the skin becomes dry, dehydrated, and susceptible to irritation and inflammation.


The epidermis is the outermost layer of skin. It contains cells called keratinocytes because they make the protein keratin. It is made up of four or five sublayers (depending on the location on the body): the basal layer, spiny layer, granular layer, stratum lucidum, and stratum corneum. Each layer has a different function.


The dermis is the middle layer of skin, located below the epidermis. It contains specialized skin cells called fibroblasts. This is where important skin components such as collagen, elastin, hyaluronic acid, and heparan sulfate are made. Only a select few topical ingredients are able to reach this layer of skin.

Stratum Corneum

The stratum corneum is the uppermost layer of the epidermis. This is where the skin barrier is located. There are 15 to 40 layers of skin cells in the stratum corneum, each arranged like a brick wall. The “mortar” between the skin cell “bricks” is the lipid bilayer that makes up the skin barrier. 


Melanocytes are specialized skin cells that produce melanin, the pigment that gives your skin its color. All humans have the same number of melanocytes, but the amount of melanin that these cells produce can vary from person to person. Melanocytes are located in both the epidermis and the dermis. They are stimulated by light, heat, hormones, stress and certain medications.


Keratinocytes are the skin cells that make up almost all of the cells located in the epidermis. These cells are created in the basal layer and work their way upward to the epidermis, pushing old skin cells up and out of the way. In the epidermis, the old cells flake off and are replaced by the new keratinocytes. Keratinocytes product the structural protein keratin.


A structural protein made in the epidermal keratinocytes. Found in the epidermis, hair and nails.  This is the substance that clogs pores and causes comedones (Black heads and white heads).


Fibroblasts are specialized cells located in the dermis layer of skin. They are responsible for producing collagen, hyaluronic acid, and elastin. They can move around in the dermis and play an important role in skin thickness, aging and wound healing. 

Skin cells

The skin is made up of many types of cells. Keratinocytes are in the epidermis, while fibroblasts are in the dermis. Melanocytes and immune cells move around in the epidermis and dermis.

Skin Care Product Characteristics


Stands for "fat loving".  Molecules that are not polar prefer to surround themselves with lipids and repel water. Lipophilic ingredients such as Vitamin E enter the cell membranes and work in these lipid environments while they avoid water environments.


Stands for "water loving". Polar molecules bind water.  The interior of the skin cell has water, so hydrophilic ingredients like Vitamin C work inside the cells.

Ingredient Categories:


Antioxidants are molecules that donate an electron in order to neutralize harmful free radicals. Antioxidants are naturally found in many plants, including berries, green tea, and ginger. Antioxidants in skincare can prevent inflammation and reduce signs of skin aging.  


Anti-inflammatory ingredients can deactivate one or more of the many inflammatory pathways that lead to inflammation.  Inflammation always consists of dilated blood vessels and redness and may lead to hives, itching and rashes depending on which inflammatory pathways are turned on. 

Skin Lighteners

Skin lighteners are a group of skincare ingredients that even skin tone. They may be called skin brighteners. They work by one or more of the following: block production of melanin,  block transfer of melanosomes from the melanocyte to the keratinocyte, or increasing exfoliation.

Tyrosinase inhibitors

Tyrosinase is the enzyme necessary to produce the pigment melanin. Tyrosinase inhibitors block this enzyme. There are many different tyrosinase inhibitors used to treat skin pigmentation problems, such as hydroquinone, resorcinol, vitamin C, arbutin and kojic acid. 

PAR-2 blockers

Proteinase-activated receptor 2 (PAR-2) is located in the connection between keratinocytes and melanocytes.  It functions as a doorway to allow melanin laden melasomes to enter into the keratinocyte after being produced by melanocytes. PAR-2 blockers prevent melanin from entering keratinocytes. Examples include niacinamide and proteins found in soy.


The skin’s natural exfoliation process is called desquamation.  When natural desquamation is not enough, exfoliants can be used to increase exfoliation. There are two types of exfoliants: chemical and mechanical. Chemical exfoliants use a low pH or enzymes to dissolve and loosen proteins attachments between skin cells. Mechanical exfoliants use friction to rub dead skin cells off of the surface of the skin.

Chemical Exfoliation-

Chemical exfoliants such as glycolic and lactic acids have a low pH and work by loosening the “glue” attachments between skin cells. This allows dead skin cells to flake off of the skin’s surface in a process called exfoliation.  

Mechanical Exfoliation-

Loofas, scrubs, brushes, and microdermabrasion devices use friction to physically remove dead skin cells from the surface of the stratum corneum causing exfoliation.

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