Skin has three main layers: the epidermis, the dermis, and the subcutaneous tissue. These layers contain substances called chromophores — including melanin, oxy-hemoglobin, and deoxy-hemoglobin.
How much light human skin reflects depends on the thickness of these layers, the concentration of chromophores, and the shapes of the skin parts. In cosmetics, the focus is mainly on melanin, oxy-hemoglobin, and deoxy-hemoglobin when it comes to evaluating things like dark circles under the eyes and age spots on the skin.
The epidermis, the outermost layer of skin, has several important substances that absorb UV light from the sun. These substances include DNA, urocanic acid, certain amino acids, melanins, and related chemicals.
Because melanins don’t dissolve easily, it’s hard to study their light absorption directly. However, indirect methods show that their absorption spectra properties change depending on what triggers their production.
This is complicated stuff, so if you’re currently feeling a bit lost, don’t worry — you’re not alone. In this article, we'll discuss what chromophores are and how they work in human skin. We’ll break it down in simple terms and answer any questions you might have about chromophores and the evaluation of different skin issues. Let’s get started!
What is a Chromophore?
A skin chromophore is a type of molecule that absorbs light at a specific wavelength and then shows color as a result. These molecules are often called “colored molecules” because of this property.
The term comes from the Ancient Greek words “chroma,” meaning color, and “phoros,” meaning bearer. There are several natural chromophores, such as chlorophyll, which make leaves appear green. The color we see is the light that is not absorbed but reflected within the visible light spectrum.
A chromophore is a part of the molecule where the energy gap between two molecular orbitals matches the energy of visible light. When visible light hits the chromophore, it can absorb the light by moving an electron from a low-energy state to a high-energy state. In biological molecules that capture or sense light, the chromophore is the part that changes shape when light hits it, allowing the molecule to respond to light.
The Different Kinds of Chromophores
There are two main types of skin chromophores. The first type of major chromophore contains only π-electrons. These electrons are found in double or triple bonds, like in the ethylenic group (C=C) and the acetylenic group (C≡C).
When light sources hit these chromophores, they can only undergo transitions between their π-electron energy levels, specifically π to π* transitions. This means that the light absorbed by these chromophores excites an electron from a bonding π orbital to an antibonding π* orbital.
The second type of major chromophore contains both π-electrons and n (nonbonding) electrons. Nonbonding electrons are lone pairs that are not involved in bonding between atoms. This type of chromophore can undergo two types of electronic transitions: n to π* and π to π*.
Examples of these chromophores include groups like the nitro group (-NO2), azo group (-N=N-), carbonyl group (>C=O), and nitrite group (-ONO). Because they have both π and n electrons, these chromophores can absorb light in different ways.
This is quite a bit of jargon, so let’s break it down in simpler terms: imagine the first type of chromophore as having only one way to jump when hit by light (like jumping from one step to another on a staircase).
The second type, however, has two ways to jump — like jumping from the floor to a step or from one step to another. This dual ability makes the second type of chromophore more complicated and capable of producing more colors when it absorbs light.
The Anatomy of Human Skin
Let’s briefly go over the anatomy of human skin so that you can gain an even better understanding of how chromophores work. Human skin consists of three main layers: the Epidermis, the upper Dermis, and the Subcutaneous layer.
The Epidermis is the outermost layer and plays an important role in the appearance and texture of the skin. It is about 0.1 mm thick on the face and is made up of four sub-layers: the stratum corneum, stratum granulosum, stratum spinosum, and stratum basale.
Beneath the Epidermis is the upper Dermis, which is approximately 2 mm thick. This middle layer contains a lot of collagen, a structural protein, and a small amount of elastin, another structural protein. It also has a network of blood vessels.
The upper Dermis produces structural proteins, glycosaminoglycans (like hyaluronic acid), and adhesive proteins such as fibronectin and laminins, which make up the Dermal Extracellular Matrix (ECM).
The deepest layer of the skin is the Subcutaneous layer (also called the hypodermis). Subcutaneous tissues mainly consist of fat and serve to protect the body from injury.
As we age, our skin layers go through changes due to oxidative stress. This can lead to a thinner upper Dermis and a less resilient Epidermis. Although aging is a natural process, it can be accelerated by external factors, like too much sun exposure.
The Role of Chromophores in Light Therapy
To understand how light-based therapy works, we first need to understand what light is. Light is a form of energy, and it exists in different frequencies and wavelengths, which together make up the electromagnetic spectrum. On this spectrum, radio waves have the lowest energy, while gamma rays have the highest. For skin treatments, the light being used is within the infrared and visible ranges.
A common question about these treatments is whether the light used can be harmful. The answer is no. Unlike ultraviolet, x-ray, and gamma radiation, which are high-energy and can damage cells, the light used in skin treatments is low-energy and non-ionizing. This means the light delivery won't cause irreversible damage to skin tissues, no matter what your skin type is.
How light therapy works
Now that we have a better understanding of light, let's look at how it’s used in skin treatments. Light-based procedures target specific molecules in the skin (yes, chromophores). The type of chromophore and the depth of light penetration needed depends on the treatment.
For example, to treat sun damage and dark spots, light targets melanin in the skin. The light targets hemoglobin in the blood to treat redness and visible blood vessels. In treatments for resurfacing normal skin or reducing hair, water, and hair follicle melanin are the targets, respectively.
When using light for skin treatments, it’s very important to be careful, especially for treatments targeting larger spot sizes. This is because the surrounding skin also contains melanin, which can absorb light and potentially cause damage. Thankfully, DermForge light therapy devices are designed to only target the affected tissue, meaning any surrounding tissue will be left unharmed.
Selective photothermolysis
The precise destruction of target tissues is achieved through a process called selective photothermolysis.
Here, the light absorbed by the chromophore turns into heat, breaking the target into smaller particles.
These particles are then cleared from the body by immune cells called macrophages.
Since melanin is most concentrated in the skin's surface layers, shorter wavelengths of light can interfere more with melanin. This isn't a big problem for people with light skin, but it does pose a risk for those with darker skin because of the higher melanin content. For darker skin, longer wavelengths are safer as they penetrate deeper and avoid the surface melanin.
Does LED Light Therapy Actually Work?
Research shows that LED light therapy can be effective in improving certain skin conditions and issues. That said, in order to see noticeable changes, you’ll need to do regular light therapy treatments. Professional LED light therapy sessions use stronger equipment than the devices available for home use, so that’s definitely something to take into consideration.
While LED masks and portable devices for home use might not produce dramatic results in reducing wrinkles or acne, they can still offer noticeable improvements in skin appearance, so it’s still worth investing in a home light therapy device or two. You’ll be able to save a lot of time and money, too, which is always a plus.
LED light therapy works by using different wavelengths of light. Each corresponds to a different color and penetrates the skin to varying depths. For example, blue light affects the uppermost layers of the skin, yellow light penetrates a bit deeper, red light goes even further, and near-infrared light reaches the deepest layers.
Each color of LED light serves a different purpose. Red LED light therapy is believed to reduce inflammation and increase collagen production, which will help you maintain more youthful-looking skin. Blue LED light therapy targets and destroys acne-causing bacteria. Some at-home devices also combine multiple colors, which means you’ll be able to kill several birds with one stone.
If you’re interested in learning more about chromophores and the science behind light therapy, feel free to check out our blog. DermForge offers the best light therapy devices on the market, so don’t forget to check those out as well! We have a wide selection of skincare products, including LED masks that provide both red light therapy and blue light therapy.