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Age Spots (Lentigines)
The brown or tan spots that appear on exposed areas of the skin can be caused by years of sun exposure. These spots, which resemble freckles but are larger, range in size from a quarter of an inch to over an inch. The spots are called age spots and sometimes referred to as "senile freckles." Future age spots can be minimized by applying high-SPF products (SPF 15 or higher although SPF 30 is strongly recommended for children under six) whenever outdoors.

Also known as Parsol® 1789, this sunscreen provides effective UVA protection and is used in combination with other sunscreens to provide broad-spectrum protection. (Parsol is a registered trademark of Givaudan-Roure Corporation.)

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Basal Cell Carcinoma
The most common form of skin cancer, basal cell carcinoma usually appears as slow-growing, translucent, raised, pearly nodules which, if untreated, may crust, ulcerate, and sometimes bleed. If detected and treated early, there is a greater than 95 percent cure rate.

A class of sunscreens which includes oxybenzone, used in many US products. These help provide the UVA and UVB protection used in many products.

Broad-spectrum Protection
This refers to sunscreen products that contain ingredients to protect against both UVB and UVA rays. For example, some broad spectrum sunscreens contain Parsol 1789 to provide extra UVA protection for those who are outdoors for long periods of time (eg, construction workers, lifeguards) or have sun-sensitive skin.

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Also known as N, N-diethyl-m-toluamide, DEET is the most common and effective active ingredient found in insect repellents today. Some sunscreen products also include DEET to help repel annoying insects for hours.

Dihydroxyacetone (DHA)
Many products on the market provide the "look" of a tan without sun exposure. Not all products are dyes or "bronzers." The chemical "dihydroxyacetone" combines with amino acids in the outer layer of the skin to produce a tan color. You control the "tanning" intensity by the frequency of use. With repeated applications, it's easy to achieve a darker tan that will not run or wash off.

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Erythema, redness due to sunburn, is a visible sign of skin damage, caused by overexposure to the sun's ultraviolet rays. The amount of sunlight needed to cause a minimally perceptible sunburn is known as the minimal erythema dose (MED).

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Homosalate is a UVB sunscreen that is often found in products with lower SPF ratings or in combination with other sunscreens in higher-protection products.

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Inactive Ingredients
Suncare products contain other components such as emulsifiers (to facilitate permanent mixing of oil and water in formulas) and preservatives (to guard against spoilage). Moisturizers are also a very important part of the formula since they soften skin and help prevent drying. Additionally, many suncare products contain a variety of special ingredients such as vitamin E and aloe. Exotic oils, such as mink, jojoba, and coconut, contribute to the cosmetic appeal and the feel of a product.

Incidental sun exposure
Incidental sun exposure is the kind of exposure received unintentionally during everyday activities. For the average person, incidental time spent in the sun is projected to account for 80 percent of his or her lifetime exposure. For this reason, dermatologists emphasize the need to protect the skin with clothing or a high-SPF sunscreen (SPF 15 or above) on a daily basis.

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The most dangerous of all skin cancers, melanoma is characterized by the uncontrolled growth of pigment-producing tanning cells (melanocytes). If detected in the early stages, melanoma can often be treated successfully, but in the later stages, it can spread to other organs and result in death.

Minimal Erythema Dose (MED)
The skin's reaction to sun exposure varies according to the individual. Each skin type is able to accept a specific amount of UV rays before burning. The amount of time an individual can stay in the sun before burning reflects the minimal erythema dose (MED). The MED and expected sun exposure, in turn, determine the proper SPF for a skin type. For example, if you burn in 20 minutes without sunscreen, an SPF of 15 allows you to stay in the sun 15 times longer (20 minutes x 15 = 300 minutes or five hours).

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This is the unit used to measure the wavelengths of solar radiation, including the shortest wavelengths—ultraviolet rays—that are responsible for sunburn, photoaging, and certain kinds of cancer.

N, N-diethyl-m-toluamide
Also referred to as DEET, this is the most common and effective active ingredient found in insect repellents today. Some sunscreen products also include DEET to help repel annoying insects for hours.

A product that is noncomedogenic will not clog the skin's pores. Noncomedogenic sunscreen products are designed for those who experience frequent or occasional "breakouts."

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A relative of homosalate, this UVB sunscreen is used in lower-SPF products or combined with other sunscreens in products of higher SPF.

A common sunscreen used in combination with other sunscreens to provide broad-spectrum protection.

A gas composed of three atoms of oxygen (O3) which partially filters out certain wavelengths of ultraviolet radiation from reaching the earth.

Ozone Layer
This is the scattered layer of ozone molecules found in the stratosphere located six to 25 miles above the earth's surface. The ozone layer partially filters out certain wavelengths of UV radiation from the sun, preventing these rays from reaching the earth.

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Para-aminobenzoic acid (PABA)
Para-aminobenzoic acid was used as a sunscreen for many years, but is no longer used for many products. PABA can stain clothing and sting skin.

Padimate 0
A PABA derivative, this water-resistant sunscreen is sometimes used for UVB protection in US products. (Also called octyl dimethyl PABA.)

Dermatologists use this term when referring to certain types of sun-induced skin damage. Photoaging is a process that starts in youth, although the more obvious skin changes, such as wrinkles, freckles, leathery texture, and loss of elasticity, may not become evident for decades. Using a high-SPF sunscreen (SPF 15 or above) on a regular basis can help protect the skin from further damage. There is also evidence to suggest that the skin has the ability to heal itself if protected, possibly reversing some of the signs of photoaging.

In certain situations, exposure to ultraviolet radiation can cause skin reactions, such as exaggerated sunburn. For example, people who are taking certain antibiotics, tranquilizers, diuretics, and other drugs may experience photosensitivity. The skin reaction may consist of swelling, itching, inflammation, or a rash. Some perfumes and citrus oils can also cause phototoxic reactions. Individuals who experience photosensitive reactions are often advised by their physicians to minimize exposure to sunlight, protect the skin with clothing, and use a high-SPF broad-spectrum sunscreen (SPF 30 or 45).

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Skin Aging
It is important to distinguish between the changes that occur normally with the passage of time from those that are the consequence of sun overexposure. Many skin changes, such as premature wrinkles, leathery skin, some freckles, and other dark spots, result from chronic, unprotected sun exposure. In fact, it is estimated that overexposure to the sun accounts for 80 percent of the effects we call aging skin. Changes that are attributable to aging include increased dryness, decreased sweating, and changes in hair growth and facial contours.

The aging process also affects the skin's ability to protect itself. The rate of cell production and turnover slows down with age, making cell repair less effective. The epidermis—the outer layer of the skin—becomes thinner, and melanocytes gradually lose their pigment-producing ability, thereby reducing the protection they offer the skin.

Those who formerly spent a great deal of time in the sun without using sunscreens can prevent further damage by using a high-SPF sunscreen on a regular basis. This action may actually allow the skin to repair some signs of sun-induced damage.

Squamous cell carcinoma
A common form of skin cancer, squamous cell carcinoma appears as nodules or red, scaly patches and can metastasize if untreated. While the cure rate is very high if treated early, squamous cell carcinoma can sometimes result in death.

The most common adverse reaction to the sun is the ordinary sunburn—also known as erythema. Burns from the sun are induced primarily by UVB radiation. The injury they cause is characterized by delayed redness and swelling followed by tanning and peeling. Sometimes the skin darkens without first reddening, but that does not mean that damage has not occurred. Chronic sun damage and sunburns especially in the first 18 years of life can result in dry, wrinkled skin and possibly skin cancer in later life.

Also see Tanning/Burning Process.

Sun Protection Factor (SPF)
The Sun Protection Factor (SPF) is a ratio between the ultraviolet dose required to produce minimal erythema reaction (redness) in protected skin (skin with sunscreen) compared to unprotected skin (skin without any sunscreen). The number indicates how many times longer a person can stay in the sun before beginning to burn while wearing sun protection than if he or she were not wearing any sunscreen at all. This amount of time varies from one individual to another. SPF numbers usually range from 2 to 50.

Most dermatologists recommend that people use a sunscreen with an SPF of 15 or higher (for children under six, SPF 30 is recommended). It should be applied evenly and liberally before exposure to the sun and reapplied often. Reapplication is necessary more frequently if the user swims, engages in sustained vigorous activity, perspires heavily, or towels off.

All sun-protection products labeled with an SPF of 2 or higher are considered sunscreens. Sunscreen agents absorb, reflect, or scatter UV light. Most lotions and oils work by forming a surface layer of sunscreening ingredients on the skin which absorb the sun's UV rays before they can penetrate the skin.

Sun-exposed Areas of the Skin
Particular parts of the body are more likely to burn due to continued sun exposure than other parts. These include the ears, lips, cheekbone area, nose, top of the head, and shoulders. Don't forget these areas when applying sunscreen. Also, protecting one's eyes with UV-blocking sunglasses is very important, since ultraviolet light may damage the eyes, leading to cancer of the eyelids and conjunctiva (the membrane covering the eyeball and lining the lids), as well as to the development of cataracts.

"Sweatproof" indicates that a product maintains its degree of sunburn protection after 40 minutes of water exposure.

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Tanning/Burning Process
When sunlight stimulates the melanocytes, they produce melanin. Melanin is the brown pigment that gives skin its tanned appearance. The darkening, or tanning, of the skin caused by melanin is one of nature's ways of protecting the underlying basal layer from further sun exposure. However, even as this natural process is taking place, sunburn can also occur, causing damage to the epidermis and the dermal layer below that. Sunburn damage occurs before you are able to see or feel it. Frequently, sunburning occurs before tanning. It is not true that a tan will completely protect skin from burning.

Titanium Dioxide, Zinc Oxide
Ingredients that reflect, absorb, and scatter UV rays are called inorganic or physical sunscreens. They form protective barriers to UV penetration of the skin and provide UVA and UVB protection.

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Ultraviolet Radiation: UVA, UVB, UVC
Ultraviolet (UV) radiation is part of the sun's spectrum—wavelengths shorter than visible light. Ultraviolet rays are divided into UVA (320400 nanometers), UVB (290320 nm) and UVC (<290 nm). The UVA spectrum is further divided into UVA II (320340 nm) and UVA I (340400).

UVB rays are more intense in summer months, at higher altitudes, and in areas closer to the equator; UVB rays are the primary cause of sunburning, premature aging of the skin, and the development of skin cancer. UVA rays are more constant, year-round, and penetrate deeper into the skin's layers; UVA rays are also harmful and contribute to burning, premature aging of the skin and the development of certain forms of skin cancer. UVC rays are blocked by the ozone layer and do not reach the earth's surface.

Tanning beds primarily emit UVA rays. This kind of exposure does not show immediate signs of damage but over time, breaks down the skin's collagen and elastic and thereby can accelerate wrinkles, leathery skin, and skin cancers.

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Water-resistant, Waterproof
"Water-resistant" indicates that a product maintains its degree of sunburn protection after 40 minutes of water exposure. "Waterproof" or "very water-resistant" indicates that the degree of sunburn protection is maintained after 80 minutes of such exposure.

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