The topmost layer of skin on the human body is called the epidermis. It defends your body from damage, keeps you hydrated, regenerates skin cells, and contains melanin, which gives your skin its color. Keep reading to know more about the layers of epidermis.

• “Cutaneous membrane” is the technical term for our skin.
• The primary role is to help protect the rest of the body’s tissues and organs from any sort of physical damage such as abrasions, chemical damage (like the ones caused by detergents), and biological damage from microorganisms.
• The skin is made up of 3 layers (From the superficial to the deepest layer):
  • Epidermis
  • Dermis
  • Subcutaneous tissue

Epidermis

• Epidermis is a thin layer of skin and is the most superficial layer as well.
• Melanocyte cells make melanin which is a natural skin pigment that determines the color of the skin.
• Two types of pigments are produced by melanocytes. This helps to determine the amount of skin pigment one has:
  • Eumelanin: Makes dark colors in one’s hair, skin, and eyes.
  • Pheomelanin: Makes pink or red pigmentation or color in one’s body (Including lips, nipples, the vagina, and the glans penis).
• Functions of the epidermis layer as a whole include:
  • Touch
  • Sensation
  • Protection against microorganisms

• Epidermis is further divided into 5 different layers:
  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum

• The Location and function of each layer of the epidermis are listed in the table given below.

LAYERS OF EPIDERMIS
Name of the epidermal layer	Location	Function
Stratum basale	Deepest layers of epidermis	New skin cells develop in this layer.This layer produces keratin layer with the help of the keratinocyte stem cells presents in it.Melanocytes which are responsible for producing melanin, which provides pigmentation to the epidermis are also located in stratum basale layers of epidermis.
Stratum spinosum	Between the stratum basale layer and the stratum granulosum layer.	Stratum spinosum mainly consists sticky proteins which hold together keratinocytes present in this layer of epidermis.This layer is responsible for the strength and flexibility of the skin.
Stratum granulosum	Between the stratum spinosum and stratum lucidum layer.	Keratinocytes have granules present within them.These granules are visible under the microscope.
Stratum lucidum	Between the stratum granulosum and stratum corneum.	It is a thin and transparent layer of the keratinocytes that are becoming less round and has a much flatter shape.
Stratum corneum	The top most layer of the epidermis.	This is the visible layer of  the epidermis.In the stratum corneum, keratinocytes become corneocytes which are strong, dead keratinocytes.Corneocytes protect us from abrasions, light, heat, and pathogens.Fat is also present in this particular layer. This helps to lock in moisture in the body.The corneocytes shed eventually as new keratinocytes develop in the stratum basale layer and move through the other layers of skin.

• The word “epidermis” combines the ancient Greek prefix “epi-”, which means “outer”, and the ancient Greek word “derma”, which means “skin”.
• Hence, the word translates to “outer skin”.

• Thickness of epidermis: 
  • In areas of skin that experience a lot of use, such as the soles of one’s feet and palm of one’s hands: 1.5 mm thick.
  • In the eyelids: 0.05 mm thick.

• The three major cells that make up the epidermis:
  • Keratinocytes: Produce keratin protein.
  • Melanocytes: They make the skin pigment known as melanin.
  • Langerhans cells: Prevent things from entering into one’s skin.

• Common conditions that affect the epidermis:
  • Melanoma
  • Acne
  • Boils
  • Eczema
  • Dandruff 

• Signs and symptoms of epidermis conditions:
  • Dark spots or growths that change shape and color
  • Peeling of the skin
  • Scaling 
  • Dry cracked skin

• Diagnostic methods to find out common epidermal conditions:
  • Allergic tests for skin: Help to find out the allergens causing the particular skin condition.
  • Blood tests: Helps to diagnose diseases and find out the allergens responsible.
  • Skin biopsy: Helps to detect diseases, infections, and cancer.

• Common treatment options for epidermal conditions:
  • Antibiotics: Helps to treat infections, dry or cracked skin, and boils.
  • Antifungal medications: Helps to treat fungal infections of the skin. Types of anti-fungal medications include creams, ointments, gels, sprays, powders, or oral medications.
  • Corticosteroids: Reduce inflammation and tissue damage.
  • Retinoids (vitamin A derivatives): Prevent acne and help to prevent clogged pores in the skin.

Dermis

• This layer of the skin is connected to the epidermis at the level of the basement membrane.
• The dermis layer houses:
  • Sweat glands
  • Hair
  • Hair follicles
  • Muscles
  • Sensory neurons
  • Blood vessels

• It consists of two layers of connective tissue:
  • Papillary layer
  • Reticular layer

Papillary layer

• It is the upper layer of the dermis.
• It lies just beneath the epidermal junction.
• It is the thinner layer of the two layers
• It consists of the connective tissue and is in contact with the epidermis.
• The loose connective tissue includes capillaries, elastic fibers, collagen, and reticular fibers. 

The reticular layer

• Is the deeper layer.
• It is the thicker layer among the two connective tissue layers of the dermis.
• It is less cellular.
• The reticular layer consists of dense connective tissue/bundles of collagen fibers which include blood vessels, collagen fibers (Arranged in parallel order), elastic fibers (which are interlaced), mast cells, lymphatics, nerve endings, and fibroblasts.

• Dermis is the thickest layer of the skin.
• Dermis is made up of fibrous and elastic tissue.
• There is a substance that surrounds the components in the dermis. Its gel-like consistency is attributed to its contents which include:
• Mucopolysaccharides
• Chondroitin sulfates
• Glycoproteins

Hypodermis

• Hypodermis is also known as the following:
  • Subcutaneous fascia
  • Subcutaneous tissue

• It is the deepest skin layer.
• Hypodermis consists of:
  • Adipose lobules
  • Skin appendages like hair follicles, sensory neurons, and blood vessels.

• The functions of hypodermis are the following:
  • Stores fat
  • Safeguards your body from mechanical injuries (Acts as a shock absorber for the internal organs of the body)
  • Connects the skin to the bones and muscles
  • Regulates body temperature 
  • Responsible for production of certain hormones like the leptin hormone.

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