October 25, 2024, 9:35 am | Read time: 5 minutes

In summer, the sun sometimes burns mercilessly from the sky. Cooling off in cold water sounds tempting – but here, too, many people underestimate the power of the sun. Even in the water, you are not completely protected from UV radiation. An expert explains what’s behind this and how you can protect yourself.

What is a sunburn, actually?

Sunburn, also known as “dermatitis solaris,” is a painful reddening of the skin caused by UV rays (ultraviolet rays) from sunlight. This radiation causes acute inflammation of the skin’s outermost layer. In some cases, sunburn can even lead to the formation of blisters^.1

Although sunburn often occurs on areas of the body that are actively exposed to the sun, it is also possible for it to occur underneath clothing. Even on cloudy days, there’s still a risk that UV rays can penetrate the clouds and reach the skin.

Which layer of skin is affected by sunburn?

Covering an area of about 1.8 square meters, the skin is considered the largest organ of the human body. It also protects the body from physical damage, infections, high temperatures and UV radiation^.2

It is composed of three layers, each serving multiple functions:

• The epidermis: This is the skin’s uppermost protective barrier and protects against external influences.
• The dermis: Provides elasticity and resilience, contains blood and lymph vessels and nerve fibers, and is also affected by the aging process.
• The subcutaneous layer (hypodermis): Functions as protection against the cold, as a displacement layer between the skin and the connective tissue sheath of the muscles and as an energy store.

The damage caused by radiation primarily affects the epidermis, which is the uppermost layer of human skin. However, it is possible that inflammatory reactions can also be triggered in the underlying layer (dermis). These often only occur hours after the actual UV exposure. Repeated sunburns over many years lead to accelerated skin aging and can increase the risk of developing skin cancer. In some cases, sunburn can lead to fever or chills^.3

Can you also get sunburnt in the water?

Even one meter below the surface of the water, UV radiation still reaches the body. According to experts, 80 percent of the long-wave UVA rays, which cause premature skin ageing and wrinkling, reach the surface. Of the short-wave UVB radiation, which typically causes sunburn, the figure is 50 percent. To prevent the dangerous rays from reaching the skin, you have to dive deeper. “At least two meters,” explains dermatologist Reinhard Mrotzek.

If you swim with your head above the waves, you should be doubly careful. The water’s surface acts like a mirror, amplifying UV radiation by 50 percent. Medical institutes such as the British National Health Service (NHS) warn against the dangerous combination of summer sun and water: the cooling effect means that you often don’t notice when your skin is burning. Mrotzek recommends applying sun cream generously and suggests that wearing headgear is “a good idea.”

Vacation abroad

According to the expert, it is also important to pay attention to the UVB light protection substance “oxybenzone.” The metabolism of “oxybenzone” results in a phototoxin that, under sunlight, becomes toxic to corals and sea anemones. Sun creams containing this ingredient should therefore not be used in the corresponding areas in the water^.4

It’s also crucial to check the expiration date on last year’s sunscreen, particularly if the package has been opened.

Does the sand on the beach increase UV radiation?

It’s not just in the water, but also on the beach that it’s easier to get sunburnt. Light-colored sand reflects the light and increases UV radiation by 25 percent, explains Mrotzek. Anyone who lies unprotected in the sand right next to the water, for example, is exposing their body to an increased risk. The same applies to a visit to a glacier. The snow there intensifies the sun’s rays by up to 90 percent.

To protect your skin from damage, it’s essential to avoid the intense midday sun in summer – between eleven o’clock and two o’clock. Experts recommend spending time outdoors in the early morning or late afternoon – especially by the water.

Does the summer sun burn just as much when it’s cool?

The same principle applies on land as in water: cool temperatures do not offer protection from the sun’s dangers, even on windy days. Dermatologist Mrotzek: “It doesn’t matter whether it’s cold or warm, the UV radiation is the same.”

The critical factors are the time of year and the time of day, which determine the sun’s position. The so-called “skin-effective radiation” reaches a power of almost 200 milliwatts per square meter on a clear day at noon on June 21. On a cloudless December 21 at midday, however, it is less than ten milliwatts.

In addition to reflections from water or snow, altitude also influences radiation. The effect of the sun increases by 20 percent at 1000 meters, by around 33 percent at 2000 meters and by 50 percent at 3000 meters compared to the intensity at sea level.

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Do you get browner after a sunburn?

“That’s absolute nonsense,” says dermatologist Mrotzek. Sunburn is an inflammation of the skin that resembles a first-degree burn or more. Dermatologists warn of permanent damage from unprotected sunbathing. Around 336,000 new cases of skin cancer are expected in 2024^.6

The UV Index (UVI) indicates the level of sun danger for the skin in different regions around the world. The World Health Organization (WHO) developed the index with other institutions. The scale ranges from 1 to over 10 and the higher the value, the faster sunburn occurs. In Germany, UVI values of a maximum of 8 are usually reached in summer.