If you’ve heard about phototherapy and its great benefits for the skin, you may have some questions about the different wavelengths, how deeply they penetrate the skin and their effects, or whether an LED mask is effective enough compared to other devices or professional treatments.
To fully understand this, it’s important first to understand which layers make up the skin and the function of each one.
How many layers does the skin have and what is their main function?
The skin is made up of three main layers:
Epidermis
The outermost layer of the skin, the epidermis, is a thin layer made up of four to five layers of cells that gradually move upward from the basal layer to the skin’s surface.
Its main functions are to protect the body from the external environment, regulate water loss, and produce new skin cells. The epidermis contains several types of cells:
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Keratinocytes: the most abundant cell type in the epidermis. They are responsible for producing keratin, a protein that provides strength and structure to the skin.
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Melanocytes: responsible for producing melanin, which gives skin its color and helps protect it from the harmful effects of ultraviolet (UV) rays.
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Langerhans cells: a type of immune cell that helps protect the skin against infections.
The epidermis also contains specialized structures such as hair follicles, sweat glands, and sebaceous glands. These structures play an important role in regulating body temperature, lubricating and hydrating the skin, and protecting it from harmful substances.
Overall, the epidermis is a crucial component of the skin, providing protection and helping regulate body temperature.
Dermis
The dermis is the second layer of the skin, located just beneath the epidermis (the outermost layer of the skin). It is a thicker layer of connective tissue that contains blood vessels, nerves, hair follicles, sweat glands, and sebaceous glands.
The dermis is responsible for providing the skin with elasticity and strength, and it plays a crucial role in regulating body temperature and protecting the body from external forces. In addition, the dermis contains several types of cells, such as fibroblasts, which produce collagen and elastin, and immune cells, which help protect the body against infections.
Hypodermis
The subcutaneous layer, or hypodermis, is the deepest layer of the skin. It is composed of connective tissue and adipose (fat) cells, which provide insulation and cushioning for the body. The hypodermis also contains blood vessels and nerves that supply the skin and the underlying tissues.
The hypodermis plays several important roles in regulating body temperature, storing energy in the form of fat, and protecting internal organs from external trauma. It also contributes to wound healing by supplying blood and nutrients to the skin.
Although the hypodermis is not technically considered part of the skin, it is closely associated with it and is often included in discussions of skin anatomy and physiology.
In the following chart, we can see a graphical representation of the skin along with information about thickness and depth measured in millimeters.
How often do skin cells renew?
The skin cells in our body are constantly undergoing a process of renewal and replacement. This is a continuous cycle that helps maintain the health and integrity of the skin.
The frequency of this renewal process depends on the specific type of skin cell, but in general, the three main layers follow these approximate timelines:
Epidermal cells
The outermost layer of the skin, called the epidermis, is made up of several layers of cells. The outermost layer, known as the stratum corneum, consists of dead skin cells that have migrated from the lower layers. This layer continuously sheds and is replaced by new cells.
It is estimated that the entire epidermis is renewed every 35–45 days.
Basal cells
These cells are located at the bottom of the epidermis and divide to produce new cells. They are responsible for generating new skin cells that will eventually reach the surface. Basal cells divide approximately every 19–23 hours.
Dermal cells
The dermis is the layer of skin located beneath the epidermis. It contains a variety of cell types, including fibroblasts, which produce collagen and elastin fibers that give the skin its structure and elasticity.
These cells do not participate in the rapid cell turnover described above and have a much longer lifespan than epidermal cells, often taking years to be replaced.
What is the skin’s hydration barrier?
The skin hydration barrier, also known as the skin barrier or epidermal barrier, is a complex system of lipids, proteins, and other substances that help maintain the skin’s hydration levels and protect it from external factors. It is primarily located in the outermost layer of the skin, the stratum corneum.
The hydration barrier has several key functions, including:
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Moisture retention: The barrier helps prevent water loss from the skin, keeping it hydrated and supple.
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pH regulation: The skin’s pH is naturally acidic, which helps protect it from harmful bacteria and fungi. The hydration barrier helps maintain this acidity.
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Physical protection: The barrier helps shield the skin from external factors such as pollution, UV radiation, and harsh chemicals.
When the skin barrier is compromised, the skin can become dehydrated, sensitive, and more vulnerable to damage. This may lead to various skin concerns, including dryness, redness, inflammation, and even infection.
To maintain a healthy skin barrier, it is important to use gentle, non-irritating products, avoid over-exfoliation, and protect the skin from environmental factors such as UV radiation and pollution. In addition, using a moisturizer can help hydrate the skin and strengthen the skin barrier.
To support and reinforce the skin’s hydration barrier, incorporating targeted skincare is key. Luminescent Bioluminescent Facial Oil is formulated with a high concentration of skin-identical and antioxidant-rich active ingredients, including 10% liposomal Vitamin C, squalane, CoQ10, and Opal Algae. These ingredients help strengthen the lipid matrix of the stratum corneum, improve skin elasticity, and protect against oxidative stress. By enhancing hydration, supporting collagen synthesis, and reinforcing the skin’s natural defense system, Luminescent helps restore balance to a compromised skin barrier while boosting radiance and overall skin quality.
And here we get to the heart of the matter: phototherapy.
How deep does light penetrate the tissues?
To understand this properly, it’s important to clarify a few key concepts about how light works. Low-Level Laser Therapy (LLLT)—also known as low-power laser phototherapy—is widely used in the treatment of many conditions. It is based on the use of light delivered through laser diodes and light-emitting diodes (LEDs).
Wavelength
Different wavelengths—identified by their color—penetrate the skin at different depths. Various researchers and scientific publications indicate approximate penetration depths in the range of millimeters:
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Blue light: 1–2 mm
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Red light: 3–7 mm
(This allows it to reach the dermis, located at approximately 2.1 mm deep, producing effects similar to retinol) -
Near-infrared light: 10–15 mm
Power
Researchers agree that penetration depth and power are not directly related, meaning that more powerful light devices do not penetrate deeper into the tissues.
Irradiation
It is also important to understand that biological changes can occur in cells that are not directly exposed to light.
This is known as the bystander effect—a phenomenon in which biological changes induced by LLLT also occur in cells that have not been directly irradiated by the incident light.
Irradiated cells can release intercellular signaling molecules, thereby stimulating neighboring cells.
In addition, the changes that occur in cells that have absorbed light photons can trigger a cascade of cellular reactions that amplify the biological response.
