How often do you apply sunscreen?

In an ideal world, everyone would adhere to the Skin Cancer Foundation recommendations and reapply sunscreen every two hours or immediately after swimming or sweating.

But the reality is often quite different.

Sunscreen loses its effectiveness over time, making reapplication vital in avoiding damage to the skin.

But now, researchers in the United Kingdom are examining the ingredients in sunscreen in the hope of developing a longer-lasting product.

“Sunscreens have been around for decades, so you'd think we know all there is to know about them, but we really don't,” Vasilios Stavros, PhD, associate professor of physical chemistry at the University of Warwick, said in a press release.

“If we better understand how the molecules in sunscreen absorb light, then we can manipulate the molecules to absorb more energy, and we can protect the molecules from degradation. If the molecule doesn't break down, there's no need to reapply,” he explained.

The findings from Stavros and his team were reported earlier this month at a meeting of the American Chemical Society (ACS).

Read more: Get the facts on sunscreen »

Chemical reactions in sunscreen

The researchers examined the chemical filters in sunscreen that absorb energy from the sun.

“UV filter molecules in sunscreens absorb radiation and convert highly toxic ‘electronic’ energy into ‘vibrational motion’ or ‘heat.’ Once the UV filter molecule has diffused this energy as heat, it is ready to reabsorb another photon of UV radiation and repeat the cycle,” Stavros told Healthline.

In some cases, the chemical filters can fail by breaking into pieces or getting stuck in the excited state.

Stavros’ team sought to determine what was causing this chemical filter dysfunction.

They used lasers to replicate the sun’s energy.

In one instance, Stavros’ team found that 10 percent of the molecules in the common sunscreen ingredient oxybenzone get stuck in the excited state when under a laser.

Stavros suggests that this finding could pave the way for chemical manipulations that would allow for a longer-lasting sunscreen.

Many sunscreens on the market are made of both chemical and physical ingredients.

Chemical ingredients work by absorbing UV radiation and preventing penetration into the skin.

Physical ingredients work by deflecting UV radiation off the skin.

Read more: Young people ignore summer skin cancer risk »

The dangers of sun exposure

However, dermatologists say many people struggle to keep to the guidelines of reapplying sunscreen.

“Compliance with sunscreen application is one of the toughest challenges — it’s easy to say ‘reapply sunscreen to exposed areas every two hours,’ not always so easy to practice,” Dr. Adam Friedman, an associate professor of dermatology at the George Washington University School of Medicine and Health Sciences, told Healthline.

“Creating sunscreens that stay active longer will no doubt improve consumer/patient compliance and allow for better protective strategies.”

The Skin Cancer Foundation recommends applying one ounce of sunscreen (about the size of a golf ball) to your entire body 30 minutes before going outside. 

“About 90 percent of nonmelanoma skin cancers are associated with exposure to UV radiation from the sun, and if you have a visible sign of sun exposure, like a tan or sunburn, this means you’ve sustained skin cell damage,” a spokesperson for the Skin Cancer Foundation told Healthline.

In the United States, more than 5 million cases of nonmelanoma skin cancer are treated in more than 3 million people each year.

Annually, there are more new cases of skin cancer than prostate, breast, lung, and colon cancers combined.

The Skin Cancer Foundation estimates 87,110 new cases of invasive melanoma will be diagnosed in the United States in 2017. An estimated 9,730 people will die of the disease this year.

Read more: Get the facts on skin cancer »

How to protect yourself

It may be a long way to go before a longer-lasting sunscreen is developed.

In the meantime, Friedman says when selecting a sunscreen, consumers should look for a product that has an SPF rating of 30 or higher, is broad spectrum, and is water resistant for up to 80 minutes.

“The best sunscreen is one you will use again and again. The kind of sunscreen selected is a matter of personal choice and may vary depending on the area of the body to be protected,” Friedman said.

He suggests creams are best for dry skin and the face, gels are good for hairy areas like the scalp or male chest, and sticks are good for around the eyes.

“It’s also important to realize sunscreen is not enough. Seek shade when appropriate, remembering that the sun’s rays are strongest between 10 a.m. and 2 p.m. If your shadow is shorter than you are, seek shade. Wear protective clothing, such as a long-sleeved shirt, pants, a wide brim hat, and sunglasses, when possible,” Friedman said.

Stavros’ research is ongoing, and he is confident the resulting data will shed more light on how sunscreens work. But he believes the future of longer-lasting sunscreens will be the result of collaborative work.

“There are a number of teams around the world working in highly complementary areas like theory, industry, research and development and getting some truly beautiful results,” he said. “I believe through collaborative efforts we can really make huge steps toward making next-generation sunscreens.”