How does the skin work?

The skin is the body's largest organ and has many important functions. One of the most vital tasks is to protect us from infections and harmful chemicals. A healthy skin barrier is crucial for performing this role. The skin has an incredible ability to repair itself and in most cases, it’s about removing what shouldn’t be on the skin so that it has the conditions to heal. You should avoid unnecessary skin products such as preservatives and perfume. 

The skin's three layers

The skin is made up of three layers. These are called the epidermis (outer skin), dermis (true skin) and hypodermis (subcutaneous tissue). Each layer consists of multiple strata, and the different layers are structured in different ways and made up of different tissue types and cells.  

Epidermis

Epidermis is covered in fats (lipids) and water that together form a protective film (the hydrolipid film). The hydrolipid film helps keep the skin supple and also provides extra protection against bacteria, viruses, and fungi. Secretions from the sebaceous and sweat glands maintain the hydrolipid film. The epidermis is made up of keratinocyte cells across five layers. Cells are created in the innermost layer of the epidermis and move over their lifetime toward the skin's surface. Along the way, the cells change and mature, a process known as keratinization or cornification. Keratinization is what distinguishes the different strata. 

Dermis

Dermis is made up of connective tissue, fibers, and proteins (collagen & elastin) that contribute to the skin's elasticity and strength. The number of elastic fibers decreases as we age, which leads to the skin becoming less supple and wrinkled. Fibers can be damaged by the sun's rays, accelerating skin aging. The dermis also contains sweat and sebaceous glands, blood vessels, sensory receptors, and hair follicles. When touched, information is sent from the dermis to the brain via nerves. Blood vessels provide nutrients and remove waste products. The dermis has a strong structure that protects the body from impacts, and the connective tissue helps wounds heal.   

Hypodermis

Hypodermis is the innermost and thickest skin layer, made up of blood vessels and connective tissue containing fat cells. Fat cells are the body's energy reserve and help regulate body temperature, as well as cushion impacts. The amount of fat we have in the hypodermis depends on our genes. The thickness of this skin layer can vary greatly. In a lean person, the hypodermis can be 2–10 mm thick, and in a person with a lot of body fat, it can be up to 10 cm thick.  

Why is it so important for our health?

The innermost layer of the epidermis is called the growth layer (stratum basale), and this is where keratinocyte cells are created. The growth layer consists of a single layer of tightly packed, brick-shaped keratinocytes. The next layer is called the stratum spinosum (prickle cell layer), and this is where keratinocytes produce keratin, a protein fiber, and take on a spiny/pointed appearance.

The next layer is called the stratum granulosum (granular layer), where keratinization begins. Keratinocytes produce granules that transform into keratin and lipids. The penultimate layer of the epidermis is called the stratum lucidum (clear layer), here the cells are flattened and tightly packed, making them difficult to distinguish. 

The final and outermost layer of the epidermis is called the stratum corneum (horny layer), which contains approximately twenty layers of dead skin cells, though this varies depending on the body part. Exposed skin, such as that on the soles of the feet, develops a thick horny layer, and calluses can form. Less exposed skin, such as that on the eyelids, has a thinner horny layer.

The pores of the sweat glands and openings of the sebaceous glands are also located in the horny layer. The cells in the horny layer are held together and bound by lipids. Lipids are vital for maintaining healthy skin, as they build the skin's protective barrier and lock in moisture. If you do not have enough lipids, the skin can become dry and feel tight and rough.

The horny layer protects against external factors such as cold. The dead cells are slowly worn away in a process called desquamation. The cells that are lost during desquamation are replaced by new cells. A cell's lifespan is approximately 4–6 weeks. The journey of a keratinocyte from the growth layer to the horny layer takes around three weeks, after which it stays in the horny layer for approximately two weeks before being worn away.