Screening Suncreens

protecting against the bright sun
Courtesy of Creative Commons

I’m one of those grocery shoppers that turns the package around to check the ingredients, before I buy anything for the first time. Checking food packages is relatively easy, because I expect only recognizable simple ingredients. As Michael Pollan says, would my Great Grandmother recognize this as food? However, what about sunscreen? You don’t really expect to know all the ingredients in sunscreen, so how can you tell if it is safe to use?

The Environmental Working Group has done extensive research to evaluate the effectiveness and safety of over 500 sunscreens currently on the market, so you don’t have to. Their fourth annual “2010 Sunscreen Guide” lists the best and worst sunscreens, and it allows you to look up information on your sunscreen. It is worth a look to make sure your current sunscreen isn’t on the “Hall of Shame” list. The Environmental Working Group also provides a lot of detailed information about sunscreen ingredients that can be damaging to your body.

This year there is concern over the large number of sunscreens with exaggerated SPF claims. There are substantially more sunscreens with high-SPF ratings in 2010, with one in six products claiming higher than SPF 50. The FDA believes that these higher ratings are “inherently misleading.” Many of these high-SPF sunscreens provide little protection from UVA radiation, the type of sunlight that doesn’t cause sunburns but does cause other skin damage and cancer. Scientists are worried that the high-SPF products will encourage people to stay out in the sun too long, increasing their risk of sun damage.

In general, most people do not use enough sunscreen to get the real benefit of the SPF rating promised on the bottle. According to the Environmental Working Group, “people typically use about a quarter of the recommended amount.” When under-applied, the typical effectiveness of SPF 100 to 15 sunscreens actually drops down to perform like SPF 3.2 to 2.

This year there is also significant concern over retinyl palmitate, which is a form of vitamin A that is found in 41 percent of sunscreens. Vitamin A is an anti-oxidant that slows aging, so it is commonly used in lotions. This may be a safe ingredient for night creams. However, a recent FDA study found that vitamin A results in the growth of cancerous tumors when used on skin that is exposed to sunlight. The National Toxicology Program is studying whether vitamin A exposed to sunlight forms free radicals that can damage DNA. Although these research studies are preliminary, the Environmental Working Group recommends that you avoid sunscreens with vitamin A (any form of retinyl or retinol).

You also need to be careful of products with hormone-disrupting compounds, such as oxybenzone which is found in about 60 percent of beach and sport sunscreens. Oxybenzone readily penetrates the skin and enters the bloodstream. This results in increased production of free radicals that may cause cancer and other health issues. The Centers for Disease Control and Prevention have found that 97 percent of Americans tested had oxybenzone in their bodies, and additional research is underway to better understand how this affects our health. So oxybenzone is considered one of the main toxic ingredients to avoid in sunscreens.

All these troubling facts may tempt you to give up on wearing sunscreen altogether. However, public health agencies still recommend using sunscreen, just not as a your first line of defense. Hats, clothing and shade are the most reliable sun protection. When that isn’t enough, then use the Environmental Working Group’s Sunscreen Guide to help you select a a relatively safe sunscreen.

I was surprised to find that my two favorite sunscreens, Neutrogena Sensitive Skin Sunblock and Alba Botanica Facial Sunblack, only rated a 4 out of 10 with “moderate” health concerns and UVA protection. So I’m also trying out some of the recommended sunscreens (rated 0-2) in search of a new favorite.

Robotic Arm Reaches Out To Knee Surgeons

Orthopedic surgeons have found a helpful hand, or more precisely a robotic arm, that will allow them to perform more accurate knee surgeries. MAKO Surgical has released a Robotic Arm Interactive Orthopedic System that is designed to assist surgeons during knee resurfacing operations. This medical robotic arm has just been selected by R&D Magazine as a winner of the 48th Annual R&D 100 Awards, identifying it as one of the 100 most technologically significant products introduced into the marketplace over the past year.

More than 10 million Americans have knee osteoarthritis, and it is the most common cause of disability in the United States. Osteoarthritis occurs when the cartilage between two bones is worn down and the bones begin to directly rub against each other at the joint. The main problem for knees is the deterioration of the articular cartilage, the smooth lining that covers the ends of the leg bones where they meet to form the knee joint. This cartilage deterioration typically leads to pain, stiffness, limited range in motion of the knee, localized swelling, and the formation of bone spurs (small growths of new bone). The pain is usually worse after activity.

Knee osteoarthritis is diagnosed based on medical history, physical examination, x-ray imaging and possibly MRI (magnetic resonance imaging). Although many people with osteoarthritis don’t need surgery, in some cases surgery is required. Surgery may involve joint replacement in which the rough worn surfaces of the joint are replaced with a smooth artificial material, such as metal or plastic pieces.

Most people affected by osteoarthritis of the knee are older than 45 years. However, some younger active patients have early osteoarthritis. Such patients with arthritis in only one area of the knee can have partial knee resurfacing surgery, which is significantly less invasive than standard total knee replacement surgery. Partial knee resurfacing replaces only the deteriorated section of the knee with a small partial knee implant, without disturbing the knee’s healthy tissue. The benefits of this less invasive surgery can be significant: smaller incision, less bone removed, less discomfort, shorter hospital stay, less physical therapy required, and more rapid healing. Since less bone is removed (about 0.25” instead of 0.5”), future total knee replacement surgery can also be more easily performed, if necessary.

However, partial knee resurfacing can be a difficult operation to perform. Using the MAKO robotic arm system to assist with the surgery will hopefully provide increased stability and precision. It also allows the surgery to be performed for a greater number of patients, since it allows the replacement of the top (patellofemoral) portion of the knee joint instead of just the inner (medial) or outer (lateral) portion. The system provides patient-specific, pre-surgical planning with 3-D modeling based on CT (x-ray computed tomography) images. The system also provides real-time visual, tactile and auditory feedback during the surgery. This should enable the orthopedic surgeons to more precisely position the partial knee implants. Hopefully this new technology will help provide a more natural feeling artificial knee and a healthier active lifestyle to some people that suffer from knee osteoarthritis.

The Workings of Fireworks

fireworks racks
Racks of cylindrical mortars used to shoot off shells into the air. Each has a fireworks shell inside, with only the main fuse visible.

My friend is a licensed pyrotechnician. Every July 4th, I help her setup and fire off a local city’s fireworks show. When you experience a fireworks show from below, you see, hear, feel and almost taste the fireworks. You are also privy to the behind the scenes drama as the fireworks is hand lit, like watching a play from back stage. It is hard to ever go back to watching the pretty lights up in the sky from far away. And it has made me appreciate fireworks more, even from a scientist’s perspective.

There is more to fireworks than pretty lights up in the sky. How are the bursts of colored light created? How do they make the different effects? How do they get up so high in the sky? There is plenty of science behind a fireworks show.

Shell being placed into a mortar.

Black powder is used to lift each fireworks shell into the air. It has been around for many centuries. It is a combination of potassium nitrate, charcoal and sulfur. If you burn black powder in the open, the heat and gas from the explosion quickly dissipates. So you put the black powder inside the bottom of the fireworks shell and place the fireworks shell inside a mortar (launch gun). This allows you to trap the heat and gas from the burning black powder, causing the gas pressure to build up until an explosion launches the fireworks shell high into the air. The fireworks shell must fit snugly in the mortar, or pressure will escape and cause a misfire. A variety of different sized shells and corresponding mortars are used to create an interesting fireworks show.

Lighting fireworks
Lit fireworks shell just before it shoots into the air.

The heart of a fireworks shell is the multiple compartments of combustible materials, called stars. Each kind of shell consists of different kinds of stars, in order to get the different colors and effects that we all enjoy. Great care goes into a shell design. Each star is made from a combination of binders, oxidizers and coloring agents. Binders (typically dextrin) are used to hold everything together. Oxidizers are used to produce the oxygen needed for the mixture inside the star to burn. The most common oxidizer is potassium perchlorate. Perchlorate ions have a chlorine atom bonded to 4 oxygen atoms, so perchlorates are relatively stable compounds that release a lot of oxygen. The fireworks colors are imparted by different metal compounds, such as: magnesium or aluminum for silver; strontium carbonate for red; calcium salts for orange; sodium oxalate for yellow; barium nitrate for green; and copper carbonate for blue.  As a star burns, the perchlorate releases oxygen and its chlorine combines with the metal compounds to form metal chlorides. These metal chlorides release energy in the form of visible light when they reach high temperatures. The color (and wavelength) of the emitted light varies with the temperature and metal compound. Blue is the hardest color to produce, because it requires a higher temperature.

A fireworks shell is ignited by lighting the main fuse. This simultaneously lights both a fast-acting side fuse and a slow time-delayed fuse. The side fuse quickly ignites the black powder to launch the shell high into the air. The time-delayed fuse burns slowly into the center of the shell as it hurls into the sky, causing the aerial fireworks display when it reaches and ignites the stars. The amount of black powder in each shell is precisely determined so that the time-delayed fuse ignites the correct star compartment when the shell is reaching the apex of its upward flight.

Fireworks Finale
Fireworks display.

A shell can also contain sound charges, creating the exciting crackling, bangs and booms to accompany the light show. When you watch fireworks, you see them much sooner than you hear them because light travels much faster than sound.

So when you watch fireworks on Sunday, you may want to think about all the science that goes on to produce the show. Or you may just want to “ooh” and “ah” in appreciation of the beautiful aerial display. Just make sure that you verbalize your pleasure, because the crew working the show will love hearing your encouragement.

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