Sunscreens
Avoiding the dangers of the sun
Types of sunscreens
Recommendations
Appropriate sunscreen selection
Sunscreen Toxicity
Introduction
Sun exposure can cause both acute and chronic injury to the skin. It is well documented that long-term sun exposure, with or without sunburn, can cause harmful effects. Long-term sun exposure has been associated with premature aging of the skin, malignant changes in the skin, development of lip cancer and corneal opacities. Skin cancer is the most rapidly increasing form of cancer in the United States. Recent studies indicate that the incidence of skin cancer is increasing at an alarming rate with 600,000 new cases being reported every year. One in five Americans will develop skin cancer in their lifetime. Skin cancer diagnosed in the early stages has almost a 100 percent cure rate. Any unusual bumps, spots, or patchy areas on the skin without a known cause should be examined by a doctor.
Ultraviolet (UV) Radiation
The UV radiation spectrum can be divided into three bands: UVA, UVB, and UVC.
Little UVC radiation reaches the earth because it is filtered out by the ozone layer. UVB radiation is the principal cause of sunburn reactions and is the wavelength band that is mostly associated with inducing skin cancer. In contrast to the effects caused by UVB, UVA radiation is responsible for causing a slow natural tan to develop. UVA radiation may also contribute to the cancer-causing potential of UVB radiation. Sunscreen lotions are more effective in protecting against shorter ultraviolet wavelengths (UVB) than against longer wavelengths (UVA).
Types of Sunscreens
Physical sunscreens are thick, solid colored substances, that are very effective in blocking both UVA and UVB radiation; however, they are messy and usually cosmetically unappealing.
Chemical sunscreens are the most commonly used and are available in a variety of formulations. They contain one or more of the UV radiation-absorbing chemicals. Some of the most widely used chemical groups that block UVB radiation are PABA (p-aminobenzoic acid), PABA esters (padimate O), cinnamates (cinoxate, ethylhexyl-p-methoxycinnamate), salicylates (octylsalicylate, homosalate), and anthranilates (methyl anthranilate). While these all block UVB radiation, the chemical group known as benzophenone (oxybenzone and dioxybenzone) provides protection against both UVA and UVB radiation.
Protection
Sunscreens have been assigned Sun Protection Factor (SPF) values by the U.S. Food and Drug Administration (FDA) since 1978. SPF is a number that refers to the sunscreen product's ability to block UVB radiation. Sunscreen products with SPFs of two to 50 are currently available. A sunscreen product with a SPF of 15 will protect your skin 15 times longer from UVB than if you did not have sunscreen applied. The exact amount of time will vary from person to person, the altitude, and proximity to the equator. SPF 15 will block 95 percent of the UVB wavelengths. SPF 30 does not work twice as well. SPF 30 will provide another 3 percent of protection.
The efficacy of a product is related not only to its SPF but also to the ability of a sunscreen to remain effective under the stress of prolonged exercise, sweating, and swimming. The following three labeling recommendations have been suggested to help the ability of a sunscreen to remain effective:
- Sweat-resistant: protects up to 30 minutes of continuous heavy perspiration;
- Water-resistant: protects up to 40 minutes of continuous water exposure; and
- Waterproof: protects for up to 80 minutes of continuous water exposure. PABA and its esters demonstrate more resistance to sweating and/or water immersion than do other chemical sunscreens.
It is recommended that sunscreens be reapplied after swimming or perspiring. However, reapplication of a sunscreen does not further the period of protection.
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Recommendations
The American Academy of Dermatology, the American Academy of Pediatrics, and the Skin Cancer Foundation recommend that protection from excessive sun exposure be initiated early. Regular use of an SPF-15 product starting after 6 months of age and continuing through 18 years can decrease the incidence of skin cancer over a lifetime by as much as 78 percent.
Recommendations for sunscreen use are as follows:
Radiation from the sun is most damaging between the hours of 10 a.m. and 2 p.m. Sun exposure should be avoided during this time whenever possible.
- Avoid artificial sources of UV radiation, including tanning beds and sun lamps.
- Wear a broad-brimmed hat, long-sleeved shirt, long pants, and sunglasses to decrease sun exposure, especially during the hours of 10 a.m. and 2 p.m. Tightly woven clothing provides the best protection.
- Surfaces such as sand, snow, concrete, and water can reflect up to 85 percent of the UV radiation. Extra precautions should be taken when around these surfaces.
- Sun exposure during childhood (up to 18 years old) is about 80 percent of an average person's lifetime exposure to the sun. Sun protection should begin at a young age and may start as early as 6 months of age.
- Use a sunscreen product with a SPF of at least 15.
- Sunscreen products should be applied 20 to 30 minutes before sun exposure.
- On an overcast or cloudy day, sunscreen use is still necessary. The clouds filter a small amount of ultraviolet radiation. Most of the UV radiation (60-80 percent) will not be filtered by the clouds and be allowed to pass through
Selection of the Appropriate Sunscreen Product
The individual's skin type is an important factor that must be considered when attempting to choose a sunscreen with the appropriate SPF. In general, very fair-skinned individuals or those with previously sun-damaged skin may benefit from high SPF products. None of the available sunscreen products are recommended by the FDA for use on children under six months of age. In addition, products with an SPF of four or less are not recommended for use on children under two years of age because they will not provide adequate sun exposure protection.
Application
Sunscreen should be applied 20 to 30 minutes before sun exposure so the product has a chance to bond with the skin. Products containing PABA and PABA-like chemicals, however, may need to be applied up to two hours in advance of sun exposure in order to achieve their maximal effect.
Using an adequate amount of sunscreen provides greater sun protection than using an inadequate amount of a sunscreen with a higher SPF rating. Most individuals do not apply enough sunscreen to achieve adequate protection.
Toxicity
Skin
No sunscreens should be used on children during the first six months of life.
Sunscreens that contain aminobenzoic acid and its esters (PABA), cinnamates, and oxybenzone can cause a skin rash and allergic photosensitivities but this is uncommon.
In May 1988, a new nitrosamine known as NPABAO was found in certain sunscreens containing padimate-O as the active ingredient. Nitrosamines themselves can be carcinogenic; however, at this time it is uncertain whether this nitrosamine is present in sufficient quantities in sunscreens to be of concern.
Miscellaneous compounds, such as fragrances, lanolin, alcohol, and preservatives may also cause skin and eye irritation or sensitization.
If Swallowed
Symptoms are unlikely with normal childhood exposure. Stomach irritation and nausea are the most common symptoms. Since PABA sunscreens contain 50 percent or more ethanol, ethanol toxicity may be the greater risk.
Many sunscreen products contain a form of an aspirin-like substance (salicylate) as their active ingredient. For example, homomenthyl salicylate (homosalate) is a sunscreen agent found in many Coppertone products. Theoretically, homosalate-containing sunscreens ingested in substantial amounts may cause aspirin (salicylate) poisoning; however, there are no such reported cases of salicylate intoxication.
Conclusion
The risks of sun exposure and its relationship to skin cancer have been well documented. Regular sunscreen use seems to help limit these harmful effects. The risks of using sunscreen products appear to be minimal. Therefore routine sunscreen use should be recommended in all individuals, especially children, exposed to the sun.
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See the expanded version of this article as a Newsletter in the Information for Healthcare Professionals Section.
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