Sun Protection and Sunscreens
Medical Author: Melissa Conrad Stoppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
Making Sense of Sunscreen Products
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor:
Barbara
K. Hecht, PhD
Most people are understandably confused when it comes to
choosing a sunscreen
because of the baffling array of available choices. Common questions about
sunscreens include
- How high should the SPF be?
- Should it block UVA or UVB?
- Does it matter whether it is a gel, cream, or spray?
- Should it be water-resistant or waterproof?
SPF stands for sun protection
factor.
The SPF numbers on a product can range from as low as 2 to as high as 60. These
numbers refer to the product's ability to screen or block out the sun's burning
rays. The SPF rating is calculated by comparing the amount of time needed to
produce sunburn on protected skin to
the amount of time needed to cause a sunburn on unprotected skin. The higher the
SPF, the greater the sun protection.
What is sun protection?
Sun protection is simply guarding a body from the adverse effects of sunlight. Aside from the hazards of heat, the sun poses the danger of sunburn, which can permanently damage the skin and cause skin cancer, precancerous changes in the skin, as well as premature wrinkling and signs of aging. Exposure to ultraviolet rays from the sun is a known risk factor for the development of both melanoma and non-melanoma skin cancers.
How is sunburn best prevented?
The best ways to avoid sunburn are to
- limit time in the sun, especially between peak sunlight hours of 10 a.m. and 3 p.m.;
- wear protective clothing, including
- a broad-brimmed hat,
- a shirt with sleeves that cover the arms, and
- a long skirt or pants with long legs; and
- use a protective sunscreen to minimize the penetration of the
sun's ultraviolet (UV) rays.
What is sunscreen?
Sunscreen is any substance or material that protects the skin from
UV radiation. Sunscreens are available in the forms of topical
lotion, cream, ointment, gel, or spray that can be applied to the
skin; a salve or stick that can be applied to the lips, nose, and
eyelids; a moistener in towelettes that
can be rubbed against the skin; sunglasses that protect the eyes; certain types of sun-protection clothing; and
film screen that can be affixed to the windows of a car, room, or
office.
What is meant by SPF?
SPF, an abbreviation for sun-protection factor, is a number such
as 15, 30, or 50 that indicates how long a topical sunscreen remains
effective on the skin. A user can determine the duration of
effectiveness simply by multiplying the SPF
by the length of time it takes for him or her to suffer a burn
without sunscreen.
For example, Mary A. normally suffers a burn in 10 minutes without
wearing a sunscreen. If she applies a sunscreen with an SPF of 15,
she will be protected for 150 minutes (10 minutes multiplied by the
SPF of 15). As another example, Jack B. normally burns in a half hour
without
wearing a sunscreen. If he also applies a sunscreen with an SPF of
15, he will be protected for 450 minutes (30 minutes multiplied by
the SPF of 15). It is important to remember that these calculations are only effective for sunscreen when it is properly applied. A common mistake is applying too little sunscreen, which can drastically reduce the effective SPF of the product. About
1 ounce (5-6 teaspoons) of sunscreen is recommended to cover the entire body. Further, sunscreen must be reapplied every
two hours when staying outdoors for a prolonged period of time. Sunscreen should also be applied at least 30 minutes before going outdoors.
People with sensitive skin who burn quickly and must spend a lot of time outdoors should always apply a sunscreen with an SPF of 30 or more.
Next: Are all sunscreens equally effective against UV radiation? »
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