Sunscreens

Definition

Sunscreens are products applied to the skin to protect against the harmful effects of the sun's ultraviolet (UV) rays.

Purpose

Everyone needs a little sunshine. About 15 minutes of exposure a day helps the body make Vitamin D, which is important for healthy bones and teeth. But longer exposure may cause many problems, from wrinkles to skin cancer. One particularly deadly form of skin cancer, malignant melanoma, has been on the rise in recent decades, as tanning has become more popular. Over the same period, scientists have warned that the thin layer of ozone that protects life on Earth from the sun's ultraviolet (UV) radiation is being depleted. This allows more UV radiation to get through, adding to the risk of overexposure.

Sunscreens help protect against the sun's damaging effects. But just how much protection they provide is a matter of debate. The sun gives off two kinds of ultraviolet radiation, called UV-A and UV-B. For many years, experts thought that only UV-B was harmful. However, recent research suggests that UVA may be just as dangerous as UV-B, although its effects may take longer to show up. In particular, UV-A may have a role in causing melanoma. Most sunscreen products contain ingredients that provide adequate protection only against UV-B rays. Even those labeled as broad-spectrum sunscreens may offer only partial protection against UV-A radiation. Those containing the ingredient avobenzone give the most protection against UV-A rays.

Some medical experts are concerned that sunscreens give people a false sense of security, allowing them to stay in the sun longer than they should. Although sunscreens protect the skin from burning, they may not protect against other kinds of damage. A number of studies suggest that people who use sunscreens may actually increase their risk of melanoma because they spend too much time in the sun. This does not mean that people should stop using sunscreens. It means that they should not rely on sunscreens alone for protection. According to the American Academy of Dermatology, sunscreens should be one part of sun protection, along with wide-brimmed hats and tightly-woven clothing that covers the arms and legs.

Sunscreens are also recommended for patients with rosacea or other skin disorders that are aggravated by exposure to sunlight.

Description

Many brands of sunscreens are available, containing a variety of ingredients. The active ingredients work by absorbing, reflecting, or scattering some or all of the sun's rays. Most sunscreen products contain combinations of ingredients.

The U.S. Food and Drug Administration (FDA) has required sunscreen products to carry a sun protection factor (SPF) rating on their labels since 1999. This number tells the consumer how well the sunscreen protects against burning. The higher the number, the longer a person can stay in the sun without burning.

Sunscreens are usually grouped into two major categories, namely chemical absorbers and physical blockers. Chemical absorbers absorb high-intensity UV rays while physical blockers reflect or scatter them. Chemical absorber compounds include avobenzone, padimate O, octyl methoxycinnamate, octisalate, and octocrylene. Physical blocker compounds include titanium dioxide and zinc oxide. The chief drawback of the physical blockers is their tendency to leave a white film on the skin, causing many people to use less of the product than they should for full sun protection.

A plant-derived compound that shows promise as a sunscreen is nobiletin, a flavonoid extracted from Citrus depressa or flat orange, a small citrus fruit native to Taiwan and Okinawa. Topical application of nobiletin has been shown to be effective in preventing the swelling and reddening of the skin associated with overexposure to sunlight.

Sunscreen products are sold as lotions, creams, gels, oils, sprays, sticks, and lip balms, and can be bought without a physician's prescription.

Recommended dosage

One should be sure to read the instructions that come with the product. Some need to be applied as long as one or two hours before sun exposure. Others should be applied 15-30 minutes before exposure, and reapplied frequently during exposure.

People should apply sunscreen liberally to all exposed parts of the skin, including the hands, feet, nose, ears, neck, scalp (if the hair is thin or very short), and eyelids. They should take care not to get sunscreen in the eyes, as it can cause irritation. People should also use a lip balm containing sunscreen to protect the lips, and reapply sunscreen liberally every 1-2 hours—more frequently when perspiring heavily or after swimming.

Precautions

Sunscreen alone will not provide full protection from the sun. When possible, one should wear a hat, long pants, long-sleeved shirts or blouses, and sunglasses. Try to stay out of the sun between 10 A.M. and 2 P.M. (11 A.M. to 3 P.M. Daylight Saving Time), when the sun's rays are strongest. The sun can damage the skin even on cloudy days, so get in the habit of using a sunscreen every day. Be especially careful at high elevations or in areas with surfaces that reflect the sun's rays, such as sand, water, concrete, or snow.

Sunlamps, tanning beds, and tanning booths were once thought to be safer than the sun, because they give off mainly UV-A rays. However, UV-A rays are now known to cause serious skin damage and may increase the risk of melanoma. Heatlh experts advise people not to use these tanning devices.

People with fair skin, blond, red or light-brown hair, and blue or light-colored eyes are at greatest risk for developing skin cancer. So are people with many large skin moles. These people should avoid exposure to the sun as much as possible. However, even dark-skinned people, including African Americans and Hispanic Americans may suffer skin damage from the sun and should be careful about exposure.

Other groups of people who should minimize sun exposure are those who have had organ transplants or recent plastic surgery. Patients who have received organ transplants have a greatly increased risk of developing skin cancer, and the facial skin of people who have had face lifts or similar plastic surgery procedures sunburns more easily than intact skin.

Sunscreens should not be used on infants under 6 months of age because of the risk of side effects. Instead, children this young should be kept out of the sun. Children over 6 months should be protected with clothing and sunscreens of at least SPF 15, preferably lotions. Sunscreens containing alcohol should not be used on children because they may irritate the skin.

Older people who stay out of the sun and use sunscreens may not produce enough vitamin D in their bodies. They may need to increase the vitamin D in their diets by including foods such as fortified milk and salmon. A health care professional can help decide if this precaution is necessary.

Anyone who has had unusual reactions to any sunscreen ingredients in the past should check with a physician or pharmacist before using a sunscreen. The physician or pharmacist should also be told about any allergies to foods, dyes, preservatives, or other substances, especially the following:

• artificial sweeteners
• such anesthetics as benzocaine, procaine, or tetracaine
• diabetes medicine taken by mouth
• hair dyes
• sulfa medicines
• water pills
• cinnamon flavoring

People with skin conditions or diseases should check with their physicians before using a sunscreen. This is especially true of people with conditions that get worse with exposure to light.

Side effects

The most common side effects are drying or tightening of the skin. This problem does not need medical attention unless it does not improve.

Other side effects are rare, but possible. If any of the following symptoms occur, check with a physician as soon as possible:

• acne
• burning, itching, or stinging of the skin
• redness or swelling of the skin
• rash, with or without blisters that ooze and become crusted
• pain in hairy parts of body
• pus in hair follicles

Interactions

Anyone who is using a prescription or nonprescription (over-the-counter) drug that is applied to the skin should check with a physician before using a sunscreen.

Resources

BOOKS

Beers, Mark H., MD, and Robert Berkow, MD., editors. "Pigmentation Disorders." In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

Beers, Mark H., MD, and Robert Berkow, MD., editors. "Reactions to Sunlight." In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

PERIODICALS

Levy, Stanley B., MD. "Sunscreens and Photoprotection." eMedicine November 25, 2002. 〈http://www.emedicine.com/derm/topic510.htm〉.

Mahe, E., E. Morelon, J. Fermanian, et al. "RenalTransplant Recipients and Sun Protection." Transplantation 78 (September 15, 2004): 741-744.

Murphy, G. "Ultraviolet Light and Rosacea." Cutis 74, Supplement 3 (September 2004): 13-16, 32-34.

Tanaka, S., T. Sato, N. Akimoto, et al. "Prevention of UVBInduced Photoinflammation and Photoaging by a Polymethoxy Flavonoid, Nobiletin, in Human Keratinocytes in Vivo and in Vitro." Biochemical Pharmacology 68 (August 1, 2004): 433-439.

ORGANIZATIONS

American Academy of Dermatology (AAD). P. O. Box 4014, Schaumburg, IL 60168-4014. (847) 330-0230. 〈http://www.aad.org〉.

American Society of Plastic Surgeons (ASPS). 444 East Algonquin Road, Arlington Heights, IL 60005. (847) 228-9900. 〈http://www.plasticsurgery.org〉.

National Institutes of Health. National Cancer Institute. 9000 Rockville Pike, Bethesda, MD 20982. Cancer Information Service: (800) 4-CANCER. 〈http://cancernet.nci.nih.gov〉.

United States Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857-0001. (888) INFOFDA. 〈http://www.fda.gov〉.

KEY TERMS

Hair follicle— A tiny pit in the skin from which hair grows.

Melanoma— A rapidly spreading and deadly form of cancer that usually occurs on the skin.

Ozone— A gas found in the atmosphere. A layer of ozone about 15 mi (24 km) above Earth's surface helps protect living things from the damaging effects of the sun's ultraviolet rays.

Pus— Thick, whitish or yellowish fluid that forms in infected tissue.

Rosacea— A chronic skin disease characterized by persistent redness of the skin and periodic outbreaks of pustules, usually affecting the middle third of the face.

Ultraviolet rays— Invisible light rays with a wavelength shorter than that of visible light but longer than that of x rays.

Sunscreen

Background

The image of a healthy person today does not necessarily include a deep, dark tan. Research has linked exposure to the sun's ultraviolet rays to skin cancer, premature wrinkles, and other skin problems. While protective clothing such as hats, pants, and long sleeve shirts are the most effective blocks against these damaging rays, sun-screen lotions also provide remarkable protection for the skin.

The light emitted by the sun consists of three frequency bands of radiation: infrared, visible, and ultraviolet. Of the three, only the ultraviolet is harmful to most humans. Ultraviolet (UV) radiation is further divided into three categories: UVA, UVB, and UVC. UVA radiation penetrates the skin without burning the surface layers. These rays can penetrate to a depth of 0.04 inches (1.0 mm) and cause damage to cell membranes and the immune system. UVA radiation has been linked to skin cancers and premature aging and wrinkling of the skin. UVB radiation is responsible for the painful, red burn people get after prolonged exposure to the sun. UVB rays also cause skin cancer and can damage the cornea and lens of the eye. The third category, UVC radiation, is generally absorbed by the earth's atmosphere and is not considered harmful. Sunscreen lotions that provide protection against both UVA and UVB radiation are known as having a broad spectrum of protection.

There are two basic types of sunscreen lotions on the market: products that penetrate the outermost layer of skin to absorb ultraviolet rays, and products which coat the surface of the skin to act as physical barriers to ultraviolet rays. Both of these types are rated with a sun protection factor (SPF), which lets the consumer know how much protection against UVB rays the product provides. The SPF of a product is the ratio of the time required for a person's protected skin to redden after being exposed to sun-light compared to the time required for the same person's unprotected skin to redden. For example, a product with SPF15 means that a person whose unprotected skin would redden in ten minutes can apply the product and stay in the sun 15 times longer, or 150 minutes, before they get a sunburn.

Researchers believed for a long time that UVB rays—the rays that actually cause a sunburn—were solely responsible for all forms of skin cancer. However, recent studies prove that UVA rays are also responsible. Although many sunscreens now contain UVA protectors, there are currently no standards set by the Food and Drug Administration (FDA) for protection against UVA rays. The SPF rating on a product applies only to protection against UVB rays. The FDA requires strict regulations and testing prior to the manufacture of any new sunscreen lotion. Sunscreen producers go through an expensive and lengthy process to get FDA approval. This approval authorizes the manufacturer to produce the exact formulation applied for and is limited to only one SPF rating and one specific usage.

Development and Testing

Today's target market for sunscreens are highly specialized. Sunscreen products are continually being redeveloped to meet the changing needs of specific consumers. For instance, formulations for athletes may contain ingredients which are more waterproof and sweatproof to provide protection for up to eight hours. Athletes may also desire a lotion that feels dry so as not to affect their grip. Children's skins are more sensitive than adults because the outermost layer is thinner. This supports the observation that most sun damage to the skin occurs during childhood and the early teenage years. Sun-screens developed for the children's market tend to contain natural ingredients such as aloe vera and vitamin E.

In the development phase for a new sunscreen, a team of chemists and lab technicians develop the sunscreen formulation from synthetic and natural ingredients. Initial formulations are made in quantities of 10 gallons (38 1) and are stored in stainless steel vats. These initial formulations are tested and finalized before an application to the FDA for approval is made. FDA approval requires further testing which may be done in-house or by an outside laboratory. Examples of the kind of testing required for FDA approval include tests to measure the effective sun protection factor according to FDA guidelines, tests to determine how safe the product is to use on the skin, and tests to measure the waterproof tolerance of a lotion.

Raw Materials

Many combinations of synthetic and natural ingredients may go into the formulation of a single sunscreen. A formulation is generally geared towards a specific SPF rating or the needs of a specific consumer group. Perhaps the best-known synthetic material used for protection against UVA rays is avobenzone, or Parsol 1789, which is used in products worldwide. Broad spectrum protection is provided by other synthetic ingredients such as benzophenone and oxybenzone, which protect by absorbing UV light. PABA (paraaminobenzoic acid) was once a popular UV-absorbing sunscreen ingredient, but it can cause skin irritation in some people and is now replaced by Padimate-O, a derivative of PABA. Other broad spectrum synthetic ingredients are octyl methoxycinnamate and menthyl anthranilate.

Titanium dioxide is a natural mineral and a popular ingredient for broad spectrum protection. Titanium dioxide works by scattering UV light instead of absorbing it. Although not as opaque as zinc oxide, it has a similar whitening effect in the higher SPF ratings. Antioxidants are often combined with titanium dioxide to slow down the oxidation of oils and thereby delay the deterioration of the lotion. Some examples of natural antioxidants are vitamins E and C, rice bran oil and sesame seed oil. Another popular antioxidant in the natural category is green tea. Many newer sunscreen products also contain skin soothing and moisturizing additives such as aloe and chamomile.

The Manufacturing
Process

Sunscreen products may be manufactured, bottled, and shipped from a single facility, or portions of this work may be handled out-side of the company. The fully automated manufacturing process described here uses some of both approaches.

Formulating the lotion

• 1 Water is purified using a method called reverse osmosis. Reverse osmosis extracts pure, fresh water by forcing water under pressure through a semipermeable membrane which separates pure water molecules from salts and other impurities.

• 2 Ingredients are purchased from outside sources and mixed with the purified water according to the recipe of the final formulation. The recipe is recorded on a vat sheet which lists the exact measurements for each ingredient. Measurements are converted from the initial 10-gallon (38 1) recipe used in the development stage to larger quantities for commercial use.

Making the containers

• 3 A blow molding facility manufactures the plastic containers for the sunscreen. In some cases this is done outside of the company. Blow molding is a method in which thermoplastics, plastics which soften when heated and harden when cooled, are extruded into a tube, called a parison, and placed into an open mold. The mold is closed around the heated parison, and the parison is pinched at the bottom to form a seal. Compressed air is blown through the top of the parison which forces the softened plastic to expand to the inside walls of the mold, creating the shape of the container.
• 4 Containers are moved to a printing facility where logos and product information are printed and, in some cases, stamped onto the containers. Stamping embosses thin metal foil onto the surface of the container in the desired shape, usually a logo. The printed or stamped containers are then stored for use when needed.

Filling the containers

• 5 Stainless steel tanks with capacities up to 1,000 gallons (3784 1) are used in the filling process. Filling takes place in a separate, sterile room with a conveyor system of many incoming tracks. Machine operators monitor the automated process. Containers and caps enter the fill room on conveyor tracks. The sunscreen lotion flows from the vats through stainless steel piping to a pressure filling machine which inserts a retractable nozzle into each container and fills it with a measured amount of sunscreen lotion.

Capping the containers

• 6 Most containers are capped automatically along the production line. Some containers include caps with pumps to allow easy dispensing of the sunscreen. These pump caps require manual assembly by operators as the containers leave the fill phase.

Shipping

• 7 The filled and capped containers are boxed in quantities of 12 to be pelletized and secured to a skid by shrink wrapping for transport to distributors.

Byproducts/Waste

Sanitized plastic scraps from the container molding process are reground and used again in molding. Containers which have been through the printing process and have flaws are passed on to other companies and made into products such as patio furniture.

The Future

Researchers look to nature in search of the next wave in sunscreen development. Some plants have natural defenses against the damaging rays of the sun. For example the single-cell alga called Dunaliella Bardawil that thrives in the Dead Sea and the Sinai desert makes its own sunscreen. Scientists at the Weizmann Institute of Science in Rehovot, Israel, isolated the protein that this plant produces when sunlight gets too intense. The protein acts as a solar deflector by funnelling light down to where photosynthesis takes place. Excess light which could interfere with photosynthesis is shunned by a yellow-orange pigment produced by the algae.

The human body also has a natural defense called melanin. Melanin is the brownish-black pigment found in skin and hair. It reflects and absorbs ultraviolet rays to provide a broad spectrum of protection. Dark-skinned people have a higher concentration of melanin and, as a result, have a lower incidence of skin cancer as well as less physical and medical signs of aging skin. Melanin was once painstakingly collected by extraction from exotic sources such as cuttle fish and cost about $3,000 per ounce ($101 per ml). However it can now be made in an inexpensive procedure using fermentation jars. One technology being used as a method of incorporating melanin into sunscreen lotions is to encapsulate it into microsponges which hold the melanin on the surface of the skin where it is most effective. The microsponges are invisible to the eye, and can only be seen under a microscope. Researchers continue to gain approval for the many uses of natural and synthetic melanin as an ingredient in sunscreen formulations.

Where To Learn More

Books

Conry, Tom, ed. Consumer's Guide to Cosmetics. Anchor Press/Doubleday, 1980.

Winter, Ruth. A Consumer's Dictionary of Cosmetic Ingredients. Crown Publishers, 1984.

Periodicals

Bylinsky, Gene. "Mass-Producing Nature's Sunscreen." Fortune, June 1992, p. 131.

Davey, Tom. "Sunscreen Success Gives Biotech New Healthy Glow." San Francisco Business Times, October 1994, p. 8.

Demetrakakes, Pan. "Packaging Patterns Make Mark On Makeup." Packaging, March 1994, pp. 20-21.

Groves, Gordon A. "Toward More Effective UVA Protection." Drug and Cosmetic Industry, August 1994, pp. 37-38.

Kintish, Lisa. "The Battle of The Sun." Soap/Cosmetics/Chemical Specialties For May, May 1993, pp. 42-48.

—David N. Ford

Sunscreens

Definition

Sunscreens are products applied to the skin to protect against the harmful effects of the sun's ultraviolet (UV) rays.

Description

Many brands of sunscreens are available, containing a variety of ingredients. The active ingredients work by absorbing, reflecting, or scattering some or all of the sun's rays. Most sunscreen products contain combinations of ingredients. Sunscreen products are sold as lotions, creams, gels, oils, sprays, sticks, and lip balms, and can be bought without a physician's prescription.

The U.S. Food and Drug Administration requires sunscreen products to carry a sun protection factor (SPF) rating on their labels. This number tells how well the sunscreen protects against burning. The higher the number, the longer a person can stay in the sun without burning.

There are three types of ultraviolet light, based on their wavelength: UVA, UVB, and UVC. UVC has the shortest wavelength and is blocked by the earth's ozone layer. Concerns about the depletion of the ozone layer focus on the serious health effects that increased exposure to UVC light would have.

UVB light is the next shortest wavelength and is called the tanning light since it is light in this range that promotes creation of the skin pigment melanin that creates a tan. UVB light only penetrates the outermost layer of the skin, but it promotes basal and squamous cell carcinoma and may worsen the effects of UVA.

Ultraviolet A is long-wave radiation generated by the sun that penetrates more deeply than UVB, causes wrinkling and leathering of the skin and damages connective tissue. UVA is the light that causes melanoma, the most serious skin cancer .

Several types of chemicals are used as sunscreens. They vary by the degree of protection they can provide and the types of ultraviolet light they can block:

• Cinnamates, such as octyl methoxcinnamate, give low levels of protection, and are only effective against UVB light.
• Para-amino benzoic acid (PABA) compounds, including PABA, padimate O (octyl dimethyl PABA), and glyceryl PABA, are effective only against UVB light.
• Salicylates, octylsalicylate, and homosalate offer moderate levels of protection against both UVA and UVB light, but the range of light waves against which they protect is relatively narrow.
• Benzophenones, including oxybenzone and dioxybenzone, protect against a broader range of ultraviolet light than the salicylates and are more useful for broad spectrum protection.
• Physical sunscreens are really sun blockers and include titanium dioxide, red petrolatum, and zinc oxide. Preparations containing these blockers are thick ointments and are usually reserved for skin areas at high risk of burn, such as the nose.

Other compounds, such as Parsol 1789 (avobenzone), Eusolex 8020, and menthyl anthranilate appear to be valuable broad spectrum agents. In one study, the combination of 3 percent butyl methoxydibenzoyl-methane and 7 percent padimate O was the most effective of all sunscreens tested.

In addition to the chemical used as a sunscreen, the vehicle can be important in determining how well a product works. Unfortunately, thick, greasy ointments seem to work better than vanishing creams, lotions, or liquids.

General use

Users should carefully read the instructions that come with the sunscreen. Some of these products need to be applied as long as one or two hours before sun exposure. Others should be applied 30 minutes before exposure and frequently during exposure.

Users should apply sunscreen liberally to all exposed parts of the skin, including the hands, feet, nose, ears, neck, scalp (if the hair is thin or very short), and eyelids. However, they should avoid getting sunscreen in the eyes, as it can cause irritation. Use a lip balm containing sunscreen to protect the lips. Reapply sunscreen liberally every one or two hours—more frequently when perspiring heavily. People should reapply sunscreen after they go in the water.

Precautions

Sunscreen alone will not provide full protection from the sun. When possible, people should wear a hat, long pants, a long-sleeved shirt, and sunglasses. They should try to stay out of the sun between 10 A.M. and 2 P.M. (11 A.M. to 3 P.M. daylight saving time), when the sun's rays are strongest. The sun can damage the skin even on cloudy days, so people should get in the habit of using a sunscreen every day. They need to be especially careful at high elevations and in areas with surfaces that reflect the sun's rays, such as off sand, water, concrete, and snow.

Sunlamps, tanning beds, and tanning booths were once thought to be safer than the sun, because they give off mainly UVA rays. However, UVA rays are now known to cause serious skin damage and may increase the risk of melanoma. Health experts advise people not to use these tanning devices.

People with fair skin, blond, red, or light brown hair, and light colored eyes are at greatest risk for developing skin cancer. So are people with many large skin moles . These people should avoid exposure to the sun as much as possible. However, even dark skinned people, including African Americans and Hispanic Americans, may suffer skin damage from the sun and should be careful about exposure.

Side effects

The most common side effects are drying or tightening of the skin. This problem does not need medical attention unless it does not improve. Other side effects are rare, but possible. If any of the following symptoms occur, people should check with a physician as soon as possible:

• acne
• burning, itching , or stinging of the skin
• redness or swelling of the skin
• rash, with or without blisters that ooze and become crusted
• pain in hairy parts of body
• pus in hair follicles

The side effects of sunscreens cannot be prevented but can be minimized by testing a sunscreen on a small area of the body before all-over applications.

Interactions

Anyone who is using a prescription or nonprescription (over-the-counter) drug that is applied to the skin should check with a physician before using a sunscreen.

Parental concerns

Sunscreens should not be used on children under six months of age because of the risk of side effects. Instead, children this young should be kept out of the sun. Children over six months of age should be protected with clothing and sunscreens of at least SPF 15, preferably lotions. Sunscreens containing alcohol should not be used on children because they may irritate the skin.

Before using a new sunscreen, particularly a newer formulation, it should be tested on a small area of skin. These products have some risk of causing rashes and other side effects.

Sunscreens should always be applied before a trip to the beach or into some other setting with intense sun exposure. Parents who start to apply sunscreen to their children upon arrival at these settings will exceed their own sun exposure limits before they begin to apply sunscreen to themselves.

Parents should consider using two to three different sunscreens at one time, to get the best results with the fewest problems. Liquids may be best for the scalp, since they can penetrate the hair. Lotions may be most appropriate for most of the body. Ointments may be the best choice for the nose and other parts of the face.

Users should always check expiration dates and not use a sunscreen past its expiration. Reapply sunscreens as directed. Children may benefit from a waterproof sunscreen. There have been claims that these sunscreens may cause eye damage, but this appears to be a hoax. There is no basis for this allegation in the medical literature.

KEY TERMS

Hair follicle —The root of a hair (that portion of a hair below the skin surface) together with its epithelial and connective tissue coverings.

Melanoma —A tumor, usually of the skin.

Ozone —A form of oxygen with three atoms in its molecule (O₃), produced by an electric spark or ultraviolet light passing through air or oxygen. A layer of ozone about 15 mi (24 km) above Earth's surface helps protect living things from the damaging effects of the sun's ultraviolet rays. Ozone is used therapeutically as a disinfectant and oxidative agent.

Pus —A thick, yellowish or greenish fluid composed of the remains of dead white blood cells, pathogens, and decomposed cellular debris. It is most often associated with bacterial infection.

Ultraviolet (UV) radiation —A portion of the light spectrum with a wavelength just below that of visible light. UV radiation is damaging to DNA and can destroy microorganisms. It may be responsible for sunburms, skins cancers, and cataracts in humans. Two bands of the UV spectrum, UVA and UVB, are used to treat psoriasis and other skin diseases.

Although sunscreen is useful, it is no replacement for subprotective clothing. While a good sunscreen has an SPF of 15 or above, denim fabric has an SPF of 1700. In contrast, a white T-shirt only has an SPF of 15, and, when wet, has an effective SPF of only 10. Sunglasses are also useful for eye protection.

Resources

PERIODICALS

Chatelain E., B. Gabard, C. Surber. "Skin penetration and sun protection factor of five UV filters: Effect of the vehicle." Skin Pharmacology and Applied Skin Physiology 16, no. 1 (January-February 2003): 28–35.

WEB SITES

"Child Care Health Program: Sun Protection for Child Care Providers." Available online at <www.metrokc.gov/health/childcare/sunprotection.htm> (accessed September 29, 2004).

Emery, David. "Sunscreen Warning Doesn't Hold Water." Available online at <http://urbanlegends.about.com/library/weekly/aa070898.htm> (accessed September 29, 2004).

"Sun Screen." Available online at <www.keepkidshealthy.com/medicine_cabinet/sun_screens.html> (accessed September 29, 2004).

Nancy Ross-Flanigan Samuel Uretsky, PharmD

SUNSCREENS

Sunscreens can be categorized as chemical sunscreens, physical blockers, or a combination of both. Chemical sunscreens contain UV-absorbing molecules that filter and limit the amount of ultraviolet (UV) radiation exposure at the skin. The most widely used chemical sunscreens in the United States contain para-aminobenzoic acid (PABA) or its derivatives, cinnamates, benzophenones, anthranilates, or salicylates. Some individuals develop allergic contact dermatitis to these compounds in sunscreens. These compounds predominantly absorb short-wave UV light (UVB) although chemicals that contain benzophenones and dibenzoylmethane (Parsol 1789) have also been developed recently to filter long-wave UV light (UVA).

Physical blockers utilize particles that reflect and scatter UV light. The more common physical blockers include titanium dioxide, zinc oxide, magnesium oxide, magnesium silicate (talc), kaolin, iron derivatives, barium sulfate, and red petrolatum. The older, opaque formulations had limited cosmetic appeal; newer blockers, however, have been combined with chemical sunscreens to give a more elegant appearance. In 1978, the Food and Drug Administration classified sunscreens as drugs and thus established standards for toxicity and quality control. The efficacy of sunscreens is measured in terms of the Sun Protection Factor (SPF). The SPF is defined as the ratio of the doses of artificial sunlight required to cause minimal skin redness with and without sunscreen. Individuals who burn easily, who are on photosensitizing medications, or who have light-sensitive diseases should diligently use sunscreens with SPFs between 15 and 30. Reapplication after prolonged sweating or swimming is recommended. Although sunscreens can provide protection against sunburns, its role in skin cancer protection remains a controversial issue. Some, but not all, studies have found an increased risk of cutaneous melanoma with sunscreen use. The most likely explanation is the individuals who use sunscreen tend to stay out longer in the sun, thereby increasing photocarcinogenesis.

Hensin Tsao

(see also: Food and Drug Administration: Skin Cancer; Ultraviolet Radiation )

sun·screen / ˈsənˌskrēn/ • n. a cream or lotion rubbed onto the skin to protect it from the sun. ∎  an active ingredient of creams and lotions of this kind and other preparations for the skin.