What is sunlight:
Sunlight consists of a spectrum of rays: visible light, ultraviolet or UV and infrared light. Each of the different rays of light in the spectrum has a distinct wavelength.
Visible light accounts for approximately 50% of the sunlight spectrum and is the only part of light that can be detected by the human eye. It has a wavelength range in the region of 400 to 760nm. The part of this visible spectrum towards the 400nm blue/violet range has a particularly high energy level and is known as HEV or high energy visible light also known as blue light.
Ultraviolet light is invisible to the human eye and comes in three forms: ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC).
UVA rays are less intense than UVB, but there are 30 to 50 times more of them. They are present constantly with equal intensity during all daylight hours throughout the year. UVB rays, however, fluctuate throughout the day and are at their strongest at noon. Both pass virtually unhindered through cloud and smog. UVC rays are completely filtered by the atmosphere and do not reach the earth’s surface.
UVB & UVA effect on skin:
UVB rays provide the energy your skin needs to make vitamin D and regulate the production of melanin which is responsible for tanning. They don’t travel as deeply as UVA rays, penetrating only the outermost layers of skin (the epidermis), however they cause more immediate damage such as sunburn and cause the skin to become thickened. UVB rays are directly absorbed by cellular DNA and can lead to skin diseases such as actinic keratosis and skin cancer. UVB, UVA, and HEV also contribute to the formation of hyperpigmentation (brown spots). UVA rays penetrate the deeper layers of skin known as the dermis. They stimulate the production of free radicals in the skin which cause oxidative stress and can lead to indirect DNA damage where the free radicals modify cellular DNA over time.
Oxidative stress from UVA & HEV:
UVA and HEV light ray interact with skin cells and generate free radicals. These free radicals are highly reactive oxygen molecules and are also known as ROS – Reactive Oxygen Species. The body uses antioxidants to neutralize these potentially harmful free radicals. When there is an imbalance between the production of free radicals and the body’s ability to neutralize them the free radicals start to damage cells in a process known as oxidative stress.
Sunlight & premature aging:
Skin aging is an entirely natural process, but when skin ages prematurely it starts to lose it’s elasticity and develop wrinkles before its time. Up to 90% of premature skin aging is caused by the sun and is known as photo-aging. The direct DNA damage caused by UVB rays plays a role in photo-aging but the main cause is the oxidative stress triggered by UVA rays and HEV light. The free radicals induced not only stress skin cells they also break down collagen and elastin which are important for smooth, plumped skin. Wrinkles form, skin loses volume and begins to sag.
The effects of sunlight on skin pigmentation:
Hyperpigmentation is caused by the overproduction of melanin which is the pigment that gives skin it’s color. The overproduction is triggered by a variety of factors but the most common is overexposure to the sun. UVA, UVB rays and HEV contribute to hyperpigmenatation, also known as sun spots.
HEV light effect on skin:
High energy visible (HEV) light is high-frequency and high-energy light ranging from approximately 380 to 500 nanometers in the blue band of the visible portion of the electromagnetic spectrum and is also referred to as blue light or near ultraviolet light. Sources of blue light include the sun, full spectrum lighting, flat screen monitors, cell phones, and tablets. Additionally, reflective surfaces, including sand, snow, water, glass, and even concrete, are sources of HEV light. Recent research has shown that HEV light generates similar amounts of reactive oxygen species, as UVA and UVB rays combined. HEV light exposure can lead to inflammation, impaired healing, hyperpigmentation, sensitivity, dryness, wrinkles, uneven tone and texture, and sagging skin.