Healthy Skin Supports Immune Health

As the body’s largest organ—spanning roughly 30 square meters—skin serves a vital function by acting as a protective barrier against environmental threats such as sunlight, rain, bacteria, and stress. Are you doing enough to safeguard this crucial component of your immune system?

Skin: A sophisticated defense system

The skin consists of three primary layers: the epidermis, the dermis, and the hypodermis.

Epidermis

The epidermis is the outermost visible layer of skin, albeit it can be as thin as a layer of tissue. This layer comprises five sublayers, with the stratum corneum being the topmost, serving as the first line of immune defense.

Within the stratum corneum, corneocytes are embedded among lipids such as ceramides, cholesterol, and free fatty acids, creating a structure similar to bricks and mortar. This design effectively prevents unwanted substances from penetrating the body while retaining essential moisture.

Keratinocytes, the predominant cell types in the epidermis, convert cholesterol derivatives into immune-boosting vitamin D with the assistance of UVB light. Another essential immune component present in the epidermis is Langerhans’ cells, which are migratory and help transport pathogens to lymph nodes.

Dermis

The dermis is the skin’s middle layer, rich in collagen, which imparts strength, and elastin, which contributes to flexibility. This layer contains nerve endings that provide sensations of pain or alert you if, for example, your hand is dangerously close to a heat source.

Hair follicles originate in the dermis, serving as sites where dendritic cells and T-cells congregate, actively surveilling for potential intruders.

This layer also houses oil and sweat glands, which, while often viewed as nuisances, play vital roles in your skin’s immune defense.

For instance, oil can help to seal hair follicles, preventing harmful microbes from penetrating deeper into the skin, while sweat regulates body temperature.

Hypodermis

The hypodermis, also referred to as the subcutis or subcutaneous layer, is the skin’s deepest layer, primarily composed of connective and fatty tissue. It enables the skin to glide smoothly over muscles and tissues, while also serving as a cushion to absorb shocks. Additionally, it provides insulation to maintain body warmth.

The skin microbiome

With such a large surface area, skin supports countless commensal and symbiotic bacteria, adding yet another protective layer as these microorganisms work to prevent pathogenic invaders from taking hold.

Interestingly, when skin is colonized by harmful bacteria, it often correlates with a reduction in commensal bacteria. The skin microbiome develops shortly after birth, with the composition of these bacterial communities being unique to each individual and remaining relatively stable over time.

When the barrier fails

Despite the numerous defenses that skin provides, its barrier function can falter, often starting with simple water loss. Water constitutes a major part of cells, making up about 60 percent of an adult’s body composition.

Dehydration can lead to various skin issues like atopic dermatitis and wrinkles. To keep your skin healthy, it’s essential to drink plenty of water and reduce transepidermal water loss (TEWL), which refers to the moisture lost from skin cells through evaporation. However, several factors can counteract this goal.

The impact of stress

Stress hormones can reduce lipids and structural proteins in the epidermis, decrease moisture in the stratum corneum, and increase TEWL. Essentially, stress has the potential to accelerate the aging process.

The role of pollution

Pollution can also weaken the skin’s barrier and increase TEWL. Studies indicate that exposure to air pollution may trigger or exacerbate allergic skin conditions such as atopic dermatitis.

The effects of topical products

The skincare products we apply can also contribute to a compromised barrier function. Foaming agents like sodium lauryl sulfate and sodium laureth sulfate may strip moisture from the skin and lead to irritation. Furthermore, certain alcohols, including isopropyl alcohol, propanol, and benzyl alcohol, can dehydrate the skin, resulting in irritation and discomfort.