Healthy skin = healthy immune system

As the body’s largest organ—about 30 square meters—skin’s primary role is to maintain a healthy barrier between you and potential harm from the elements, including sun and rain, bacteria and germs, and stress. But are you protecting this important ally of your immune system?

Skin: A complex system of protection

The skin comprises three major divisions or layers, including the epidermis, the dermis, and the hypodermis.

Epidermis

This layer of your skin is the part you can see and touch. Despite the fact that it can be about as thin as tissue paper, the epidermis itself contains five sublayers. The uppermost sublayer is the stratum corneum, and it’s the first line of immune defense.

Cells called corneocytes in the stratum corneum are interspersed with lipids (ceramides, cholesterol, and free fatty acids) to resemble bricks and mortar. This organizational structure helps prevent entry of foreign substances into your body while at the same time trapping precious water.

The most common cell types in the epidermis are keratinocytes, which play a role in converting cholesterol precursors into immune-supporting vitamin D with the help of UVB light. Other critical immune cells in the epidermis include Langerhans’ cells, which are migratory cells that transport pathogens to the lymph nodes.

Dermis

Skin’s middle layer, or dermis, houses collagen that gives your skin strength as well as elastin that provides flexibility. Nerves located here keep you safe by triggering pain or letting you know, for example, when your hand is too close to the stove.

Hair follicles are rooted in the dermis and seem to be a gathering place for dendritic cells and T-cells on the lookout for invaders.

The dermis is also where we find oil and sweat glands. While you may consider the products of these glands to be an annoyance, they play critical roles in your immune defense.

Oil, for example, may help to seal hair follicles so that unfriendly microbes can’t enter deeper layers of the skin. It also helps repel water. Sweat helps you maintain a healthy body temperature.

Hypodermis

The hypodermis (also known as the subcutis or subcutaneous layer) is the deepest skin layer and consists primarily of connective tissue and fatty tissue. This layer allows skin to move smoothly over tissue and muscle and to act as a shock absorber. The hypodermis also insulates your body to protect you from the cold.

Skin’s microbiome

Given its extensive surface area, skin provides room and board to millions of commensal and symbiotic bacteria. This adds an extra layer of protection, as these bacteria help prevent colonization and invasion by pathogenic microbes.

In fact, skin occupation by pathogenic strains is usually associated with low numbers of commensal or neutral bacterial strains. The skin microbiome populates shortly after birth. Bacterial communities are site specific and individual to the person, and they tend to be fairly stable over time.

Barrier breakdown

Despite various skin fortifications, barrier function can be compromised—and it might start with simple water loss. Water is the main component of cells and represents 60 percent of adult body composition.

H2O deficiency is associated with skin dysfunction, including atopic dermatitis and skin wrinkling. To keep skin healthy, you want to drink plenty of water and minimize transepidermal water loss (TEWL) or the moisture lost from skin cells through evaporation. But there are a lot of things working against that goal.

Stress assaults

Stress hormones decrease lipids and structural proteins in the epidermis, decrease hydration in the stratum corneum, and increase TEWL. In other words, stress can age you.

Pollution

Air pollution may also compromise skin barrier function and encourage increased TEWL. Researchers suggest that air pollution may trigger or worsen allergic skin conditions such as atopic dermatitis.

Topicals

The products we apply to our skin can also cause a breakdown in barrier function. Common foaming agents such as sodium lauryl sulphate and sodium laureth sulphate can strip away valuable moisture and cause skin irritation. Alcohols such as isopropyl alcohol, propanol, and benzyl alcohol may also rob your skin of moisture and leave your skin feeling irritated and sore.