Proteins are made of building blocks known as amino acids. Human proteins are made of various combinations of 20 of these. A diet especially rich in one of them — arginine — appears to help the immune system. It can fend off infections and at least one type of cancer, finds a new study in mice.

Arginine appears to ramp up the immune system’s ability to spot danger. A high-arginine diet seemed to offer the rodents some protection against flu and COVID-19 viruses. It also quashed colon tumors, says Sohail Tavazoie. A doctor and cancer biologist, Tavazoie works at Rockefeller University in New York City.

His team shared the new findings July 30 in Cell.

“I don’t want the takeaway to be that everyone should be just consuming arginine all the time,” says Tavazoie. It’s just too soon, he says, to know if taking it as a food supplement could prevent or even treat these diseases in people. But he’s interested in launching human studies to test that.

The new data do make a compelling case for further testing, says Costas Lyssiotis. He had no role in the new study. But he is a cancer researcher at the University of Michigan Medical School in Ann Arbor.

Might a high-arginine diet help the human immune system recognize tumors and target them for destruction? That’s not yet clear, Lyssiotis says. But, he adds, it’s something that is “super provocative and should be pursued.”

Not ‘essential’ — but beneficial

Research has been suggesting that arginine may play an outsized role in disease.

Nine amino acids are considered “essential” nutrients. That’s because our bodies use them but can’t make them; they must be acquired as part of what we eat. Arginine is not one of those. But because this amino acid can open blood vessels, some people do take arginine as a food supplement. The goal is to help their blood circulate.

Arginine also tends to be scanty in the lungs of people with influenza or COVID-19. It’s barely present, too, in the tumors that develop in people with colon cancer. What’s more, studies have shown that both cancer and viral infections can crank up the destruction of arginine.

Tavazoie’s team wondered what was so important about this amino acid that multiple diseases shut it down.

In the lab, his group tinkered with arginine levels in mouse and human cells. Cutting back on arginine reduced levels of key immune proteins, they found.

Take what’s known as MHC class 1 proteins. Riding on the surface of our cells, they tell the immune system what to watch out for. Like a police officer holding up a sketch of a criminal, they display snippets of viral or cancer proteins. But the immune system has trouble recognizing and rousting those outlaws when cells have fewer MHC-1 proteins than normal. 

A key player in immunity?

Tavazoie’s team then turned to mice at risk of colon cancer. When the researchers fed them a low-arginine diet, MHC-1 levels fell and the number of colon tumors rose. But add bonus arginine to the diet — what would be about 10 grams a day for humans — and the outcome flipped. Now MHC-1 levels rose and tumor-forming fell.

These data suggest dietary arginine can control MHC-1, a very important group of immune proteins, Tavazoie says.

Arginine-starved cells slowed their assembly of MHC-1 proteins. That may be because these proteins contain long stretches of arginine units. If there aren’t enough of these building blocks available, “there’s a supply-chain shortage,” he says. At that point, MHC-1 construction stalls.

The team observed a similar story in mice infected with the flu virus or the virus that causes COVID-19. Low-arginine diets led to them having low levels of MHC-1 proteins. They also had more viral proteins and inflammation in their lungs compared to mice eating high-arginine diets.

This suggests arginine was blunting the effects of infection. And arginine supplements given after flu infection boosted mouse survival, the team found. That points to it as a possible treatment one day. Tavazoie now wonders whether other amino acids may play similarly important roles.

There’s still much work needed to know if the mouse data predict effects in people, says Pierre Close. He’s a cancer researcher at the University of Liège in Belgium. He didn’t participate in the new study. But, he says, this research might one day lead to therapies that help the immune system better tackle disease. “We are all looking for new strategies.”

Glowy oils, tinted creams, misty sprays, chalky sticks, lightweight gels. Like many people, my pool bag is filled with many types of sunscreen. But all use the same sun-shielding chemicals. In fact, the allowed ingredient list for U.S. sunscreens hasn’t changed in 20 years — until now.

This June, the U.S. Food and Drug Administration (FDA) added bemotrizinol (Beh-moh-TRIZ-eh-nol) to its approved list.  

“I think we should all be super excited,” says Tanya Hathaway. She’s a dermatologist who specializes in treating high-risk skin-cancer patients. Hathaway works at the Fred Hutchinson Cancer Center in Seattle, Wash.

Bemotrizinol has many benefits. It lasts longer than other sunscreen ingredients. It won’t get quickly absorbed into the bloodstream. And it’s very good at blocking those rays of the sun that age skin.

Sunscreens in Europe have used the chemical for more than 25 years, Hathaway notes. More recently, it’s been approved in Japan, Canada, Australia and many other places.

There are some sunscreen ingredients used elsewhere that still are not allowed in U.S. products. Bemotrizinol’s approval could open U.S. doors for some of these. It’s “a great first step,” Hathaway says.

A new chemical sunscreen

Sunscreens use a few tricks to protect our skin from the sun’s rays. Physical sunscreens rely on minerals such as titanium dioxide and zinc oxide. These create a coating that reflects sunlight, like a mirror. But they can leave a white sheen on the skin. Just think of a lifeguard’s nose, says Jennifer Stein. She’s a dermatologist at NYU Langone Health in New York City.

Those zinc and titanium products also “don’t rub in so well,” she notes. “And if people don’t like the way their sunscreen smells or feels, they’re not going to use it.”

Non-mineral sunscreens often rub in a bit better. They often use chemicals such as avobenzone (Ay-vah-BEN-zoan) and oxybenzone to absorb the sun’s rays. But these molecules are not very stable. They start to break down when hit by sunlight, Stein says. That’s not ideal for something that’s designed for use in the sun.

Because bemotrizinol is more stable, people may not need to apply sunscreens with it as often. This new ingredient also is good at blocking ultraviolet A1 (UVA1) radiation. That’s a type that gets deep into the skin. Over time, UVA1 can make skin wrinkly, loose and spotted, Hathaway says.

Current U.S. sunscreens do a good job of blocking UVB, which causes sunburns. But U.S. sunscreens had fewer options for blocking UVA, she says. Bemotrizinol “really expands that UVA spectrum of coverage.”

Is it safe?

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You might have seen influencers on TikTok or Instagram making DIY sunscreens. Often, they will call the ingredients in commercial brands “toxic.” Sunscreen skepticism on social media is nothing new, Stein says. Patients who avoid sunscreen often worry about chemicals passing through the skin.

That can happen with things like avobenzone and oxybenzone. They may even get into your blood, Stein says — but only if “you apply them to large areas of the body repeatedly throughout the day.” Even so, people shouldn’t fear them. Hathaway says no studies have shown that U.S. sunscreen ingredients are unsafe when used at current levels.

Bemotrizinol, which is a big molecule, is less likely to pass through skin than these other chemicals. It’s “too big to squeeze through the skin cells to get down into your bloodstream,” Stein says.  

FDA classifies bemotrizinol as GRASE (short for generally recognized as safe and effective). Titanium dioxide and zinc oxide are the only other U.S. sunscreen ingredients with this rating.

Bemotrizinol’s U.S. approval goes into effect on August 9. So sunscreens using it could hit shelves later this summer. But a new sunscreen is not the only way to stay safe from the sun. There are plenty of low-tech options, too: long sleeves, hats, sunglasses and staying in the shade. “The more clothing you’re wearing,” Stein emphasizes, “the less you have to depend on sunscreen.”

Meteorites that are billions of years old. Alienlike worms. A blue whale’s massive jaw bones. These are just some of the millions of marvels at the Smithsonian Institution.

Most are part of the Smithsonian’s National Museum of Natural History collection, a trove of nearly 150 million objects. It includes a spectacular array of preserved life forms, rocks and cultural artifacts from around the world.

Few people have ever seen this vast collection of astonishing objects. The museum in Washington, D.C., only displays a small share of the items. Most sit tucked away in huge storage pods at the Smithsonian’s Museum Support Center (MSC). This site in Suitland, Md., is not open to the public.

But Science News was able to get a behind-the-scenes peek.

Lining MSC’s hushed halls are rows of cream-colored cabinets and kilometers (miles) of shelving. Scientists led us through long corridors, pointing out prime treasures along the way. We saw and touched an abundance of specimens that captivate the mind and eyes. Some items even had odors — like a freeze-dried crabeater seal. It smelled like burnt soy sauce.

But MSC is not just a giant storage unit. It’s a place scientists visit to do research and answer big questions about our planet. Forget the idea that museums are old and dusty, says Kirk Johnson. He’s the director of the National Museum of Natural History. Museums, he argues, are “vastly more vibrant and more important” than most people realize.

A protected collection

MSC opened in 1983 when the Smithsonian needed more space for items in its already overcrowded natural history museum. Each of the center’s five storage pods is about the size of a football field. And they’re nearly three stories tall. A sixth pod is in the works.

Their key goal: Protect the specimens.

MSC carefully controls the temperature and humidity inside each pod. It also shields these storage areas against pests.

Security guards patrol the premises 24/7. Along the way, they watch for power outages, floods, flames and explosions. Huge freezers need power to keep tissues and DNA samples ultracold. Dried specimens can be damaged by fire and water. And wet items in alcohol-filled jars are at risk of drying out — or blowing up.

MSC’s stash is part of a “forever” collection. They’re available to study today and in the future. Scientists are now, for instance, analyzing African elephant DNA stored here. The elephant that this genetic material comes from is thought to belong to a population that has long evaded humans.

Past work on bird eggs collected decades ago helped reveal that the insecticide DDT had built up in their shells and thinned them. This nearly drove some species — including the bald eagle — to extinction. Evidence of DDT’s harm to wildlife helped lead the United States to ban the chemical in 1972.

“There’s a cloud of knowledge about the planet that exists only because we have collections in museums,” Johnson says.

Scientists who work here are passionate about the knowledge stored in MSC’s pods. As we moved from one area to another, staff members would race to show us “just one more thing!” A coil of feathered money, for instance, that was once used on the Santa Cruz Islands in the South Pacific.

Items stowed at the MSC or on display at the museum represent everything that we know about the planet, says Rebecca Johnson. She’s the museum’s chief scientist (and unrelated to Kirk). “This is the record of the world,” she says.

In an age of AI, it can be difficult to tell truth from fiction. But MSC’s treasures let us see and touch and smell and study our planet’s reality. “People still want to know what is real,” Rebecca Johnson says. “This is the place where we have the real thing.”

Let’s go on a field trip

Our private MSC tour introduced us to a colossal cache of objects. We saw items that dazzled and brought chills. We wanted to photograph everything. In a place that’s home to millions of objects, how do you pick what to feature?

We chose items with an eye to what stood out in size or peculiarity. We also focused on those with intriguing backstories. We could fill entire books with photos and the histories of these items. Instead, we’ll highlight our favorites.

Most likely to haunt your dreams

Most likely to make you feel very small

Most likely to keep calm and carry on

Biggest buzzkill

Best dressed

Biggest stinker

Most likely to be mistaken for a mushroom

Most likely to make you take a closer look

Most likely to strip the flesh from your bones

Finest feathers

Most likely to ghost you