Skin Layers and How They Protect You (2024)

The number of skin layers that exists depends on how you count them. You have three main layers of skin—the epidermis, dermis, and hypodermis (subcutaneous tissue). Within these layers are additional layers. If you count the layers within the layers, the skin has eight or even 10 layers.

Skin is the largest organ in the body and is quite complex. Its primary function is to act as a barrier against disease-causing pathogens (germs) and hostile environments. It also helps regulate body temperature and gathers sensory information from your environment.

This article looks at the three main layers of skin and the layers within them. It explains the different types of tissue found in the layers of the skin and the conditions that affect them.

The Epidermis

The epidermisis the outermost skin layer. Its thickness depends on where it is on the body. It's thinnest on the eyelids (roughly half a millimeter) and thickest on your palms and soles (1.5 millimeters).

Conditions and disorders that affect the epidermis include:

• Acne
• Boils
• Dandruff
• Eczema
• Melanoma

It is made up of the following five layers.

Stratum Corneum

The stratum corneum is the top layer of the epidermis. Its jobs are to:

• Helps your skin retain moisture
• Keep unwanted substances out of your body

It is made of dead, flattened cells called keratinocytes that are shed approximately every two weeks. Keratinocytes produce keratin, a fibrous protein that helps provide structure to your skin, hair, and nails.

Stratum Lucidum

The stratum lucidum is a separate layer only in the thicker epidermis on the palms of the hands and soles of the feet. In thinner areas, its cells and functions are incorporated into other layers.

The stratum lucidum:

• Allows the skin to stretch
• Contains a protein that helps skin cells degenerate
• Protects your palms and soles from the effects of friction
• Makes your skin waterproof

This layer is also made of dead, flattened keratinocytes.

Stratum Granulosum

The stratum granulosum layercontains keratinocytes that are gradually being pushed toward the surface of the skin. While moving through this layer, cells start to lose their structure and characteristic and become more like the dead, flattened keratinocytes of the outermost layers.

This skin layer also contains lipids (a type of fatty acid) that help form a waterproof barrier that prevents your body from losing fluid through the skin.

Stratum Spinosum

The stratum spinosum, or squamous cell layer, is the thickest part of the epidermis. It contains:

• Newly formed keratinocytes
• Langerhans cellsthat help fight infection

This is the main barrier that keeps foreign substances in the environment from getting into your body.

Stratum Basale

Also called the basal cell layer, the stratum basale is the bottom layer of the epidermis. It contains several important types of cells:

• Column-shaped stem cells that push older keratinocytes toward the surface, where they flatten and die
• Melanocytes, which produce pigments that gives your skin its color
• Merkel cells, which sense touch
  

The Dermis

The dermis is the middle layer of the skin. It contains connective tissue, capillaries, nerve endings, and hair follicles. It also contains different glands, including sebaceous glands that produce sebum (a body oil) and apocrine glands that produce sweat.

Conditions and disorders that affect the dermis layer include:

• Autoimmune collagen disorders such as scleroderma
• Chronic sun damage (solar elastosis)
• Genetic collagen disorders such as Ehlers-Danlos and Marfan syndromes
• Hives (urticaria)
• Tumors, such as dermatofibrosarcoma protuberans (DFSP)

The dermis is split into two parts.

Papillary Dermis

The papillary dermis is the thin, upper layer that contains capillaries (tiny blood vessels) that help regulate skin temperature and provide nutrients to the epidermis.

This skin layer also contains the following:

• Meissner corpuscles, which are receptors that transmit sensations of delicate touch
• Lamellar corpuscles, which are receptors that transmit sensations of vibration and pressure

Reticular Dermis

The reticular dermis is the thick, lower layer that contains connective tissues and dense collagen bundles.

Collagen is the main protein that provides structure to skin and connective tissues. It gives skin elasticity and strength.

The thickness of the dermis varies by its location on the body. On the eyelids, it is roughly 0.6 millimeters thick. On the back, palms of hands, and soles of the feet, it's 3millimeters thick.

Hypodermis

The innermost layer of the skin is the hypodermis. Also known as subcutaneous tissue, it's mostly made up of:

• Fat
• Connective tissues
• Larger blood vessels
• Nerves

The majority of your body fat is stored in the subcutaneous layer. It insulates you against changing temperatures and protects your muscles and internal organs from impacts and falls.

In medical shorthand, subcutaneous is abbreviated SQ. An SQ injection is delivered to the subcutaneous layer.

The hypodermis layer also does the following:

• Stores fat cells for energy reserves
• Gives the body its smooth, contoured appearance
• Regulates temperature through the contraction and dilation of blood vessels
• Serves as the attachment point for bones, muscles, and other organs to the skin
• Contains deep pressure sensors
• Produces a hormone called leptin that helps keep the body's metabolism in homeostasis (balance among all of your body's systems so they can function well)

Conditions that affect the subcutaneous layer of the skin include:

• Bedsores
• Hypothermia
• Panniculitis
• Sarcoidosis
• Third-degree burns
• Tumors

Summary

The skin is the body's largest organ. It is made of three layers, each of which has specific functions.

The outermost epidermis is responsible for producing new skin cells, protecting the body from unwanted substances, and retaining moisture to keep the skin well hydrated.

The middle dermis is responsible for supporting and strengthening the skin. It helps keep the skin moisturized and nourishes the epidermis. It also aids with fine sensations and helps regulate the skin temperature.

The innermost subcutaneous tissue insulates the body against changes in temperature and physical impacts. It gives the body its contoured shape and connects the skin to the internal organs. It also stores fat cells for energy and helps regulates the body temperature,

By Heather L. Brannon, MD
Heather L. Brannon, MD, is a family practice physician in Mauldin, South Carolina. She has been in practice for over 20 years.