“The sun never repents of the good he does,” said Benjamin ­Franklin, one of the ­Founding Fathers of the USA. “Nor does he ever demand a ­recompense.” It rises every day and we think nothing of it, but without the sun our planet would be uninhabitable.    

The sun, a giant nuclear reactor, ­provides us with the heat and light that are essential to all life on Earth. Its rays also help our bodies make vitamin D, which in turn helps us absorb calcium and phosphate from our diet – minerals that are important for healthy bones, skin and muscles. It boosts our immune systems and releases mood-­enhancing serotonin. But too much exposure to the sun’s ultraviolet (UV) radiation is ­detrimental to everything on Earth – humans, animals, plants and objects. Dermatologists say there is no such thing as a “healthy” tan. Tanned skin is damaged skin.

Ultraviolet radiation from the sun reaches us in wavelengths between 100 and 400 nanometers (billionths of a meter). Around five percent of UV ­radiation is UVB, which only penetrates into the ­epidermis, while 95 percent is UVA. This can ­penetrate far deeper, though both UVA and UVB rays can cause skin ­cancer. And it’s not just humans that need ­protection – animals do too. In ­Cambodia, rats trained to sniff out deadly landmines need to have their ears covered in sunblock to allow them to carry out their life-saving work.

The reason for reddening

General awareness about the risks of sun exposure is growing, but it was only in the last decade that researchers, led by Professor Richard Gallo, Chair of the Department of Dermatology at UC San Diego, USA, discovered why our skin reddens.

It is part of a process to alert the body that it is in danger. When skin cells are damaged by UV rays, it causes a type of ribonucleic acid (RNA) within those cells to break up. Our bodies become aware of the damage to the RNA because it is detected by what are called ­receptor ­molecules in neighboring cells. The ­receptor ­molecules instruct the body to inflame the skin around the damaged cell – which is what we experience as sunburn. “The reason for the inflammation is to clear away the sun-damaged cells,” says Gallo. “But it’s not only clearing, it’s actually alerting the body that the damage has occurred so you can have the appropriate response.”

As well as tests on human skin cells, the team carried out a study in mice and found that those without the receptor molecules did not have as much of a ­redness response. “At one point everything became predictable as a pathway,” says Gallo. Thanks to the research we now know that the receptor molecules are part of a process that warns us that our skin has been exposed to too much sunlight.

The right protection

While countries like Australia are doing a good job of getting sun safety ­messages across, others have a great deal of work to do, Gallo believes, with tanning still widely associated with exercise and ­outdoor activity. Cancer Research in the U.K., for example, has found a 150 percent rise in skin cancer deaths since the 1970s. “There’s this common misperception that tanning is healthy. But it’s very clear that there’s damage going on,” says Gallo.  

Sunscreens to protect us from this damage have developed considerably since the first widely available product, developed by Austrian Franz Greiter, went on sale in 1946 with a sun protection ­factor (SPF) of just two. Getting the UV filters exactly right, however, can still be a ­difficult balancing act, as products need to protect against the different kinds of UV rays while still feeling pleasant on the skin. 

There are two types of UV filter: organic filters based on carbon, and inorganic filters based on zinc and titanium oxide. Organic compounds absorb UV light while inorganic particulates not only absorb but reflect and scatter the light. One organic example is BASF’s Tinosorb^® M. Around 90 percent of its action is via absorption and the rest through scattering. “We’ve chosen the most efficient ­molecules – an SPF 50 formulation absorbs 98 ­percent of the incoming UVB light, which is ­incredible with such a thin film,” says Marcel ­Schnyder, Head of the Global Technical Center Sun Care at BASF in Grenzach, Germany. Sunscreen products made with it have a light texture and dry feel, while meeting the UVA protection guidelines of the European Union.