Safe Sun : Cancer Fear Takes Sunscreens Out of Dark
Increasing consumer awareness of what a variety of medical experts characterize as an epidemic of sun-related cancers has moved sunscreens from near obscurity to the front lines of preventive health.
With the prominence, however, has come confusion over how sun prevention products are rated, how consumers can make a reasoned choice about which to use and what sunscreens can and cannot do.
Technically, according to the U.S. Food and Drug Administration, a sunscreen uses chemicals to filter the sun’s rays and allows some tanning to occur, while a sunblock is completely opaque, blocking any ultraviolet rays from penetrating to the skin. In practice, however, the two terms tend to be used synonymously.
Sunblock and sunscreen ratings--whose meaning was arcane, at best, until the last year or two--are based on a system of measures of sun protective factors, or SPF, starting at 1.
The rating system indicates the comparative extra time a person could spend in the sun wearing a certain product compared to using no block. An SPF rating of 15, for instance, means that if an individual could spend 30 minutes in the sun before burning with no lotion on, 15 times that amount of time--or 7 1/2 hours--could be safely spent wearing the product, provided it does not wash off because of perspiration or water exposure.
Two Types of Ultraviolet Rays
But what the sunscreen rating system doesn’t immediately tell a consumer, Dr. Ronald Reisner and Dr. Richard Strick of ULCA and other experts agreed, is that no product currently on the market effectively filters out one of the two types of ultraviolet rays emitted by the sun.
Skin can be damaged by what are called ultraviolet-B and ultraviolet-A rays--commonly called UVB and UVA. UVB is the type against which commercial sunblocks are effective and these rays are responsible for most skin damage associated with sunburning. They do not penetrate the epidermis--the outermost layer of the skin.
But UVA rays--a type emitted by many kinds of common tanning parlor machinery--penetrate beyond the epidermis and can damage collagen, a key element in the skin’s connective tissue system. Impaired collagen can allow premature wrinkling, and UVA is also thought to be capable of harming the body’s immune system--which may in turn lead to skin cancer.
There is an apparent synergism between UVA and UVB, said UC San Francisco’s Dr. Richard Odom, because UVA damage deep in the dermal layer seems to worsen what UVB does to the epidermis.
Dr. Arthur Sober, a Harvard University skin cancer expert, said 15 sunblocks provide chemical filtration effective against 92.5% of UVB rays. Only half of the remaining 7.5% are eliminated by a block rated 30, he said, indicating a point of diminishing return.
Skin cancer experts agree that sunblocks effective against UVA are likely to appear on the market soon--perhaps within the next year. But at the moment, they say, sunblock is medically effective against only UVB, although some manufacturers claim partial effectiveness against UVA in some so-called “broad spectrum” products.
According to over-the-counter drug regulators of the U.S. Food and Drug Administration, products that currently claim “broad spectrum” status filter only “a moderate amount” of UVA rays. However, the FDA confirmed that a new class of possibly prescription-only sunscreens able to filter UVA as well as UVB are in the final stages of pre-market government approval.
Since UVB remains the most immediate threat to sun worshipers, however, these same experts call for far wider and intelligent use of available products.
A sunblock should be applied a half hour before sun exposure begins so the chemical molecules that actually filter out the sun’s rays can bind to the skin. Many products are effectively waterproof and stand up to swimming, but perspiration compromises almost all of them. Screens should be reapplied hourly if a person is sweating or goes for more than a brief swim.
Ratings War
According to the SPF scale, dermatologists interviewed by The Times agreed, products rated at more than 15 may serve little purpose because they provide for a degree of sun exposure no one is likely to encounter. But sunblock makers have gotten into something of a ratings war, with products rated at 30 and even--this year for the first time--50.
The rating situation amuses Menlo Park dermatologist Dr. Faye Arundell, who said the effectiveness of sunblocks actually improves little after the 15 rating--though all of the doctors involved agreed that, to generations of tanners accustomed to ratings of 2 and 4, a 15 may seem radical of itself.
“There are not many days when you can stay out 15 times 30 minutes,” she said. “From 15 on, the amount of additional sun protection is minimal.”
Thickness of Application
But UCLA’s Reisner said dermatologists should not dismiss use of higher-numbered products because it is often difficult to determine whether a sunblock that is designed to be invisible once it is on the skin has been applied thickly enough to work.
“If you don’t put the sunscreen on thick enough, you don’t get as much protection,” Reisner said. “It is basically a chemical trapping of the energy of the sun by the molecules of the sunscreen. If you have fewer of those molecules, it doesn’t work as well.
“I think there may be some advantage theoretically in using a higher SPF to make up for the differences in effectiveness as a result of different thicknesses. It seems to me there’s nothing to be lost by using a 30 and there might be something to be gained, even though, for the average person, 15 is plenty and any more than that is probably gilding the lily.”
Standard Ingredients
Most sunblock products rely on a small number of comparatively standardized basic ingredients, the oldest of which is PABA--or para-aminobenzoic acid, a derivative of chemistry naturally found in the body. A chemical called oxybenzone is also widely used. Molecules in the blocks bind to the skin and prevent the passage of UVB rays.
For parents of very young children, however, the chemistry of sunblocks creates special problems. Most skin specialists believe that most commercial sunblocks are probably not toxic to babies, but definitive scientific studies necessary to resolve the question have not been completed.
Today, said Arundell and other specialists, many dermatologists discourage parents from using sunscreens on their babies except for what are called physical sunblocks, or zinc-oxide based products that form an opaque covering on the outside of the skin itself. Babies should probably be sheltered from direct sun as much as possible, experts said, though Reisner said he is confident enough of the lack of toxicity of commercial sunscreens that he would not hesitate to use them on infants.
SUNBLOCKS MADE SIMPLE Sunblock is opaque and blocks all sun; sunscreen chemically filters some ultraviolet rays but allows some to pass through to the skin for tanning. In practice, the terms are used interchangeably. The sun protective factor, or SPF; a multiple indicating the total time a person wearing the product can safely remain in the sun compared with not wearing sun protection. A person using 15 could remain in sun 7 1/2 hours and experience the same burning as 30 minutes with no protection--or 15 times the unprotected exposure. Waterproof indicates the sunscreen should offer protection for at least 80 minutes while swimming. A water-resistent product should last a minimum of 40 minutes in water. All sunscreens lose effectiveness in perspiration and must be reapplied. Most common active ingredients include para-aminobenzoic acid , or PABA, and oxybenzone. Both bind to skin, chemically filter sun’s rays. A true sunblock uses zinc oxide as a physical barrier against sun rays.
