Skin and the sun – How do the sun’s UVA, UVB and HEVIS light rays affect skin

Sunlight, in moderation, is good for us, but overexposure to the sun can damage skin both on the surface and at a cellular level. This article looks at the different rays that make up sunlight, examines the positive and negative effects those rays have on skin condition and outlines the factors that influence the way your skin reacts to the sun.

Sunlight consists of a spectrum of rays: visible light, ultraviolet (commonly known as UV) and infrared light. Light is measured in wavelengths – the units of which are nanometers (nm) and millimeters (mm). 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, as the name suggests, 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 high-energy visible (HEVIS) light or HEVL.

Infrared A and B rays have a longer wavelength of between 760nm and 1000nm (1mm) and – like UV rays – are not visible to the human eye. They account for the remaining 45% of light.

Sunlight can be good for us, but too much sun causes skin damage. Sunburn, photoaging (premature skin aging caused by the sun), hyperpigmentation and sun allergies are examples of visible skin damage, but the effects of sun exposure can go even deeper, causing DNA damage at a cellular level.

UV rays (both UVA and UVB) are the main cause of sun-induced skin damage but high-energy visible (HEVIS) light can cause further stress to skin. The rays affect skin in different ways:

UVB rays provide the energy your skin needs to make Vitamin D, they stimulate 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), but they cause more immediate damage such as sunburn and can cause skin to thicken temporarily. UVB rays are directly absorbed by cellular DNA and can lead to skin diseases such as actinic keratosis and skin cancer.

UVA rays penetrate the deeper layers of skin (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). UVA rays are most commonly associated with:

• Photoaging (premature skin aging caused by the sun): 
• Sun allergies such as PLE (UVB rays can also provoke allergies, but to a lesser degree)
• Hyperpigmentation such as sun spots (also known as age spots)

Like UVA, HEVIS light penetrates the deeper layers of skin and generates free radicals that cause oxidative stress. These free radicals are one of the main causes of photoaging. They interfere with skin cells and break down the collagen and elastin that gives skin its plump and youthful appearance. HEVIS light is also linked to hyperpigmentation.

How does the sun cause oxidative stress? 

UVA and HEVIS light rays 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 is an important source of Vitamin D which is essential for many of the vital processes in our body: it keeps our bones healthy and may lower the risk of depression.

Studies have shown that the rate of serotonin production in the brain is directly affected by the amount of sunlight the body is exposed to that day. Serotonin levels are higher on bright days than on overcast or cloudy days. Serotonin is a powerful brain chemical that controls mood and is associated with happy feelings.

Similarly, people who have reduced exposure to sunlight, usually in the winter months in the northern hemisphere, can experience symptoms of depression, difficulty concentrating, low energy or fatigue and excessive sleeping. Together these symptoms are classified as Seasonal Affective Disorder (SAD).

Skin aging is, of course, an entirely natural process, but when skin ages prematurely it may start to sag and develop wrinkles before its time. Up to 90% of premature skin aging is thought to be caused by the sun1 and is known as photoaging. The direct DNA damage caused by UVB rays plays a role in photoaging but the main cause is the oxidative stress triggered by UVA rays and HEVIS 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 hyperpigmentation issues such as sun spots (also known as age spots) appear prematurely.  

1.  Ramos-e-Silva et al., ‘Anti-aging cosmetics: Facts and controversies’. Clin Dermatol. 2013 Nov-Dec; 31(6): 750-8.

Hyperpigmentation is caused by an overproduction of melanin – the natural pigment that gives skin its color. This overproduction can be triggered by a variety of factors but the most common is overexposure to the sun. UVA, UVB and HEVIS light rays are all connected with pigmentation issues and may contribute to conditions such as age spots (also known as sun spots) and melasma.

Research suggests that a propensity to sun allergies is genetic, but that 80% of cases are triggered by UVA rays. When people have the underlying condition, their immune system identifies and reacts against areas of skin altered by the sun producing a rash.

The UVB rays that lead to sunburn and damage the cellular DNA directly can, in the worst cases, cause skin diseases such as actinic keratosis (dry, red or brown scaly patches of skin that can be painful but are harmless if treated) and skin cancer.

Physicians and dermatologists warn increasingly about the strong correlation between the sun and skin cancer. There are three main types of skin cancer:

Our geographic location, the season, the climate and the time of day all impact on the intensity of the sun’s rays. The amount of time we spend in the sun, and the way in which we protect our skin from it, has a considerable impact on skin health by limiting the

Different skins react in different ways to the sun:

• Tone: Pale skin can be more prone to sunburn while darker skin is often more susceptible to hyperpigmentation.
• Age: Children’s skin and mature skin is thinner and more fragile than skin at other ages and is particular sensitive to sun damage.
• Location: Some areas of skin – such as the face, neck, décolleté, arms and hands – are more exposed to sun than other parts of the body. 
• Type: Oily and acne prone skin has different sun protection needs to dry skin 
• Condition: The sun can trigger sun allergies, and those taking certain medications, as well as people who have recently had a chemical peel or laser treatment, may find that their skin is more sensitive to the sun.