Fancy a brighter, whiter smile? You’re not the only one. An estimated 35.22 million people in the US are expected to use some sort of tooth whitener this year – but do any of the most popular methods they might end up using actually work?Before we get started, it should be noted that it’s normal to not have perfectly white teeth – genetics, aging, medications, and certain diseases (or even just your daily coffee fix) can all cause discoloration. But if you’re set on whitening your chompers – or are simply curious – read on to find out which methods work, and which are a bit more questionable.DIY methodsCharcoalScrubbing your teeth with activated charcoal – “activated” it’s undergone a process to make it more porous, with a larger surface area – is perhaps one of the most widely claimed ways to whiten them. You’d be hard-pressed to find a big-name drugstore that doesn’t stock some sort of charcoal powder or toothpaste for whitening.  However, those claims are unfounded. In a 2017 review published in the Journal of the American Dental Association, researchers found there was “insufficient scientific evidence” to support that charcoal powders and pastes can whiten teeth – nor was there enough evidence to say they’re safe to use either (although activated charcoal on its own is likely safe in the short-term when it’s ingested, but be cautious if you take any medications by mouth as it can decrease absorption).There’s also a possibility that it could end up damaging your teeth. According to the American Dental Association (ADA), use a powder that’s too abrasive and could wear away the enamel, the teeth’s protective covering. Do that over a long enough period of time and you might achieve the opposite of what you set out to do – worn-away enamel exposes a yellow layer called dentin underneath.Baking sodaBaking soda is another favorite of at-home teeth whitening proponents and to be fair, on its own, can do some short-term whitening. As ADA spokesperson and dentist Dr Matt Messina told CNN Health, it has mild abrasive and bleaching properties, but tread carefully – like charcoal, that can eventually cause damage.“You might see short-term whitening with an abrasive, as it will remove surface stains and teeth may get whiter quickly, but the long-term damage is in no way worth that,” said Messina.Another oft-touted method is combining baking soda with lemon juice. In theory, the two should neutralize each other – one’s basic and the other’s acidic. Attempting to get that balance right at home, however, probably isn’t worth it; as with the abrasiveness of baking soda, the acidity of lemon juice can also wear away enamel.Drugstore productsWhile baking soda and charcoal might’ve been around for longer, the shelves of drugstores are now stacked with apparent teeth-whitening products, from strips and pens to gels and pastes, to save you from making your own concoctions.Do they work? It’s difficult to know for each and every one, and it doesn’t help that manufacturers don’t even necessarily have to prove that they’re effective. In the US, lots of teeth whitening products – even some containing the bleaching agent hydrogen peroxide – available in stores could legally be considered as “cosmetics” and thus aren’t subject to FDA approval, which would otherwise require rigorous testing and evidence to show that the products can live up to their claims.Some products, however, carry the ADA’s “Seal of Acceptance”. Though, under the law, it’s not the same thing as getting FDA approval, the ADA does require safety and efficacy data from lab or clinical studies, which is then examined by a panel of experts, in order for a product to get the seal.One product that’s yet to receive the seal is purple toothpaste, which has shot up in popularity over the last year or so.It works on the same principle for yellow-stained teeth as purple shampoo does for yellow-ish bleached hair – yellow and purple are opposite each other on the color wheel, so bung some purple toothpaste on and the stains should be neutralized, leaving you with pearly whites.This might have immediately visible effects – but will it last? Speaking to Health, Jason Cellars, DDS, gave that a firm no."People see instant results because the purple hue turns the yellow hue of your teeth white," said Cellars. "Unfortunately, this illusion is short-lived, and your teeth will only appear whiter until the toothpaste fully washes off."At the dentist’s officeOften the most expensive of the teeth whitening options is getting it done by a dentist. This might include enamel microabrasion – achieving the same thing as baking soda might, but faster – or more well known, the use of gels or solutions containing the bleaching agent hydrogen peroxide.As Gennaro Cataldo, a professor of general dentistry at the Henry M. Goldman School of Dental Medicine, told BU Today, these solutions are “totally different from the material you buy in the drugstore.”“It’s highly concentrated; the gums actually have to be protected from this material,” said Cataldo.While it’ll cost you, the procedure is effective; according to Cataldo, the whitening effect can last up to two years.Though done professionally, this method of teeth whitening can still have side effects, such as a short period of tooth sensitivity and/or irritated gums. Some dentists offer tray-based treatments to use at home as a cheaper alternative to the in-office procedure, which might bump up the risk of these side effects given that it’s partly unsupervised.The bottom lineThere’s a myriad of methods that claim to be effective at whitening teeth, but whether or not something actually works, if you’re planning on teeth whitening, it’s best to visit the dentist’s office before you do.Not only is that because it’s always a good idea to make sure your teeth are healthy – especially if you’re going to be doing something abrasive to them – but it can also give you an idea of which method might be best for you.“Whitening may not work on all teeth,” says the ADA, “and if you are a candidate, some methods – whether at-home or in the dental office – may be better for your teeth than others.”All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.  The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.  

A popular natural rock feature that stood for millions of years has come crashing down into Lake Powell in Utah’s Glen Canyon National Recreation Area. Known as the Double Arch, the stunning geological attraction had been one of the park’s most visited beauty spots, but collapsed on Thursday, August 8th.Also known as the Toilet Bowl, Crescent Pool, and the Hole in the Roof, the mesmerizing structure formed from 190-million-year-old Navajo sandstone and had the appearance of an enormous skylight in a grotto, allowing sunlight to illuminate a glittering patch of water in Rock Creek Bay. According to a statement from the National Park Service (NPS), the ancient structure had been shaped and warped by the elements since its formation, causing it to continually erode and break apart.This process may have been influenced by the changing shoreline of Lake Powell, which the NPS says has been declining since 2001 as a result of climate change and a prolonged drought. “Changing water levels and erosion from wave action is suspected of contributing to the ultimate collapse of the arch,” confirmed the federal agency’s statement.Double Arch as it was before Thursday's collapse. Image credit: National Park Service.“This event serves as a reminder of our responsibility and need to protect the mineral resources surrounding Lake Powell,” added Glen Canyon National Recreation Area Superintendent Michelle Kerns. “These features have a life span that can be influenced or damaged by manmade interventions. While we don’t know what caused this collapse, we will continue to maintain our resource protection efforts on Lake Powell for future generations to enjoy,” she said.Stretching from Lees Ferry in Arizona to the Orange Cliffs of southern Utah, the Glen Canyon National Park covers an area of around 5,060 square kilometers (1.25 million acres) and includes several world-renowned natural landmarks. Among these are the hugely popular Horseshoe Bend on the Colorado River and Rainbow Bridge, which is among the world’s largest natural bridges.Fortunately, the NPS was able to confirm that no one was injured by the collapse of the Double Arch. Yet with millions of tourists passing through the national park each year, Kerns highlights the need for all visitors to respect the delicate nature of these ancient natural wonders. “Please enjoy our resources but leave no trace,” she says.

Look at a map of faults and fault lines in the US, and much of it will look pretty much like you’d expect, assuming you’ve ever heard of the San Andreas Fault. Basically, there’s nothing between the East Coast and, oh, Denver or so, and then suddenly the country turns into a mess of seismic activity and potential.There’s one anomaly to that rule: a big old hotspot right in between the Ozarks and Appalachia. Known as the New Madrid Seismic Zone, it’s been home to some of the largest and most destructive quakes in US history – and nobody really understands why.What is the New Madrid Seismic Zone?It was two a.m., on December 16, 1811, when the first earthquake struck the frontier town of New Madrid, Louisiana Territory. It was “a violent shock of an earthquake,” wrote New Madridian Eliza Bryan in 1816, “accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating, which was followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness.”They’re generally referred to as three earthquakes, but the truth is that it was more like one three-month-long biblical apocalypse. The initial quake – a magnitude 7.0 mother – was felt across an area of nearly a million square miles, or 3.5 Texes; the ground was felt shaking as far away as Canada, church bells rang from the motion in Boston, and chimneys were brought down in Cincinnati, Ohio. It was followed by aftershocks and weaker earthquakes until, on January 23, the area was hit by a second major quake of magnitude 7.3; after that, the “earth was in continual agitation, visibly waving as a gentle sea,” Bryan wrote, until on February 7, the strongest earthquake yet – magnitude 7.5 – hit the town again.People and animals alike panicked and fled as the ground was “horribly torn to pieces,” Bryan recounted, with great fissures “vomit[ing] forth” black, coal-like substances mixed with sand and water. The Mississippi River rose up “fifteen or twenty feet perpendicularly,” she wrote, and appeared temporarily to reverse course; it was literally rerouted so much that it created Reelfoot Lake in Tennessee, and the banks of the river were covered in dead fish and wrecked boats.In the end, the whole town had sunk about 15 feet lower than before – there are even photos of trees that have grown a second set of roots to deal with the new ground level – and the whole area was dealing with aftershocks for years afterward. It was, Bryan admitted, “a scene, the description of which would require the most sublimely fanciful imagination.”Tree with a double set of roots, a result of the New Madrid earthquakes.USGS/Public domainAnd that’s only the most recent spate of quakes. Paleoseismology – the study of ancient earthquakes via evidence in the geological record – has revealed a pattern of seismic activity in the region: we now know that the New Madrid region was devastated not only in 1811, but also in about 1450 CE, 900 CE, 300 CE, and 2350 BCE.Not only are earthquakes fairly regular in the area, then, but they’re also startlingly consistent. By studying liquefaction features – the size and composition of sand blows; their locations and distributions, and so on – researchers have been able to conclude that these historical earthquakes were strikingly similar to the events of 1811-12: they were “similar in location and magnitude to the 1811-1812 earthquakes,” the United States Geological Survey (USGS) notes, and likely “also […] were earthquake sequences.”Overall, the USGS explains, “the New Madrid seismic zone generated magnitude 7 to 8 earthquakes about every 500 years during the past 1,200 years.” And yes: it’ll probably happen again; it’ll probably be bad; and it probably won’t be alone.And here’s the thing: none of that really makes any sense at all.Why do earthquakes happen?We like to think we know what causes an earthquake. “Earthquakes result from a ‘stick-slip’ motion, where rocks ‘stick’ along fault planes while stress accumulates until a ‘slip’ occurs – a bit like pulling on a stuck door until it suddenly opens,” wrote Åke Fagereng, a researcher in Cardiff University’s School of Earth and Ocean Sciences, in a 2020 article for The Conversation.“This slip also releases energy as the seismic waves that, in large magnitude earthquakes, create substantial damage.”This is why earthquakes are so commonplace in places like Alaska, Southern California, Japan, and everywhere else in the so-called “Ring of Fire” – the infamous tectonic belt around the Pacific Ocean inside of which some 90 percent of the world’s earthquakes occur. It’s why places like Iran and Afghanistan see so much seismic activity – the countries are sat on top of multiple fault lines, with the Indian and Arabian tectonic plates subducting under the Eurasian plates.All of which raises the question… why would Missouri be in trouble?What’s going on in Missouri?If earthquakes are caused by the interaction of various tectonic plates – what the heck is going on at the New Madrid Seismic Zone?“It’s a big mystery,” USGS geologist Eugene Schweig told Wired in 2008. “New Madrid is about as far from a plate boundary as you can get.” While they’re rare, earthquakes within tectonic plate interiors do happen – but why is a question that geologists are struggling with even today. “It is generally agreed that these intraplate earthquakes are caused by reactivation of old rifts,” explained Attreyee Ghosh, a professor from the Centre for Earth Sciences at the Indian Institute of Science, in a 2020 article for the European Geosciences Union. “However, what causes this reactivation is not well-understood.”For the New Madrid Seismic Zone in particular, there’s a whole slew of potential answers, Ghosh noted: suggestions include “glacio-isostatic adjustment, weakening of mantle due to rifting or arrival of a plume, ridge push, gravitational body forces, large scale mantle convection as well as dynamic topography,” to name but a few. Her own preferred theory features long wavelength tectonic stresses, with intraplate earthquakes effectively being activated by massive forces propagated in from the tectonic boundary.Whatever is reactivating these rifts, it’s clear that the New Madrid Seismic Zone is the result of old, old geology. Researchers have located three fault lines in the region which were formed about 500 million years ago – “a time when the North American plate tried and failed to pull itself apart,” explains Undark. But precisely why these fault lines are still active – or newly reactivated – is a mystery. And that’s a big problem.See, without a clear mechanism for what’s causing the quakes, researchers are at a loss for ways to predict them. Being located smack dab in the middle of a tectonic plate makes normal methods all but moot: it’s only within the last decade that they were even able to confirm geological movement in the area at all, let alone figure out how much tectonic stress is being held in the ground – or where the breaking point may be.“We know from research and past events that we’re capable of having large earthquakes in this area again, and at any time,” Brian Blake, executive director of the Central United States Earthquake Consortium, told Undark. “Our job, regardless of the mechanism that causes earthquakes, is to prepare.”How much danger is the New Madrid Seismic Zone in?So, how worried should Missourians – and Tennesseans, Arkansans, Kentuckians, and Illinoisans – be? Well, it depends on what precisely you’re asking.The actual risk of an earthquake, especially one similar in severity to the three that battered the state back in the 1800s? That’s probably not very high: “we would estimate a 25 – 40 percent chance of a magnitude 6.0 and greater earthquake in the next 50 years,” notes the USGS Earthquake Hazards Program, “and about a 7 – 10 percent probability of a repeat of the 1811-1812 earthquakes in the same time period.”In fact, it may even be lower than that. The extent to which the New Madrid Seismic Zone has been touted as a potential disaster area – by the media, and even by other scientists – has been criticized by some experts. There are questions over the methodology used by the USGS, which is based on probabilistic techniques; deterministic or scenario analyses, which are favored by geologists at the University of Kentucky, result in a lower risk profile, and – at least, according to the methods’ proponents – a more accurate one.That said, earthquakes are notoriously difficult to predict – and even a very low risk of seismic activity can only tell half the true story. Alaska gets more earthquakes than any other state in the union, including some of the highest-magnitude ever recorded – but in 2018, when Anchorage was hit by a magnitude 7.0 earthquake, there was only minimal damage and zero deaths.How did they manage that? It’s simple: in a state where seismic activity is commonplace, earthquake preparedness is built into everyday life. Schools regularly drill students on what to do in a quake; buildings must adhere to strict codes and standards; family homes get kitted out with emergency provisions and exit strategies in preparation for disaster.Not so in New Madrid. The eponymous Seismic Zone covers several major cities – Memphis, Tennessee; St Louis, Missouri; Little Rock, Arkansas, each with populations in the hundreds of thousands – and “we know that a lot of people are living in buildings that are not ready for a big earthquake,” Jeff Briggs, the earthquake program manager for the Missouri State Emergency Management Agency, told Undark.And while efforts are afoot to shore up the area’s earthquake awareness, it’s slow going. Funding is low, and legislation is lacking; thanks to their rareness, earthquakes in general are simply “not as front of mind” as other natural disasters, Briggs explained.Nevertheless, he added, when the next major earthquake hits – and all evidence suggests that it will – “it’s going to be the biggest natural disaster this state has ever experienced.”

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