Sunlight, Ultraviolet Radiation, and the Skin
National
Institutes of Health
Consensus Development Conference Statement
May 8-10, 1989
This statement was originally published as:
Sunlight, Ultraviolet Radiation, and the Skin. NIH Consens Statement 1989 May 8-10;7(8):1-29.
For making bibliographic reference to the statement in the electronic form displayed here, it is recommended that the following format be used:
Sunlight, Ultraviolet Radiation, and the Skin. NIH Consens Statement Online 1989 May 8-10 [cited year month day];7(8):1-29.
NIH Consensus Statements are prepared by a nonadvocate, non-Federal panel of experts, based on (1) presentations by investigators working in areas relevant to the consensus questions during a 2-day public session; (2) questions and statements from conference attendees during open discussion periods that are part of the public session; and (3) closed deliberations by the panel during the remainder of the second day and morning of the third. This statement is an independent report of the consensus panel and is not a policy statement of the NIH or the Federal Government.
It is ingrained in humans to love light and, indeed, since mankind's first wanderings from the caves, worship of the sun has been a fundamental tenet that many societies hold even to the present.
The properties of the sun that have inspired such reverence include its light (visible radiation) and its warmth (infrared radiation). Additional portions of the solar spectrum that cannot be perceived directly by the senses (ultraviolet) are capable of evoking both physiologic and pathologic events in the skin.
Sunlight is the ultimate source of energy and is vitally important to life as we know it. However, absorption of incident solar energy by components of the skin can cause a variety of pathological sequelae.
Until the 20th century, the sun was the predominant source of human skin exposure to energy within the photobiologic action spectrum. More recently, artificial devices capable of mimicking the emission of some or all of the solar spectrum have been introduced, compounding the opportunities and risks of ultraviolet radiation (UVR) exposure.
Despite the undeniable importance of cutaneous exposure to ultraviolet radiation for vitamin D homeostasis, there is little evidence to indicate that there are additional beneficial effects of such exposure. Indeed, overwhelming evidence exists to support the concept that the skin is damaged in many different ways by its direct exposure to natural or artificial UVR. Some exposure is virtually unavoidable over a lifetime and is dramatically dissimilar in different populations depending upon climate, geography, occupation, and recreational activities. The consequences of this exposure are also influenced by factors such as the degree of melanin pigmentation. The effects of UVR can be divided into two general types, acute and chronic. Acute effects include sunburn, and chronic effects include, among others, the development of certain forms of skin cancer. In addition, the skin is a major site of immunologic activity, and UVR is capable of affecting the immune system via its effects on the skin. The skin is also susceptible to degenerative changes evoked by chronic UVR. These changes are a major component of the constellation of physical changes perceived as skin aging but, which in reality, are due to chronic photodamage.
It is now possible to measure the effects of solar radiation on the skin, and epidemiologic studies from around the world have provided important new knowledge concerning the risks and benefits of exposure to sunlight and UVR.
Expanding knowledge about the hazards of exposure to sunlight and UVR has been accompanied by improved approaches to photoprotection, including the development of more effective sunscreen formulations. In addition, there is increasing interest in pharmacologic agents such as the retinoids that may be capable of inhibiting the development of or possibly even reversing certain chronic effects of cutaneous sun exposure.
Considerable controversy remains concerning the specific adverse effects caused by various wavelengths of UVR, the magnitude of the adverse effects, and potential strategies for their prevention and/or treatment. A Consensus Development Conference was undertaken in an effort to define the specific interactions of sunlight, UVR, and the skin as well as to identify methods for preventing and/or treating the adverse effects of UVR. Sponsored by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, the Office of Medical Applications of Research, the National Cancer Institute, and the National Institute of Child Health and Human Development of the National Institutes of Health, the Food and Drug Administration, and the Environmental Protection Agency, the conference brought together physicians, scientists, and other health care professionals, along with representatives of the public on May 8-10, 1989. Following 1 1/2 days of presentations and discussions by the invited experts and the audience, members of the consensus panel drawn from the biomedical research community and the public weighed the scientific evidence in formulating a draft statement in response to several questions:
In applying the recommendations of this consensus conference, it is important to recognize that special circumstances may exist for each patient. These may include unavoidable exposures to UVR or the inability to use certain of the preventive strategies. There are clearly some areas in which final recommendations cannot yet be made due to insufficient data. In these situations, physicians must use their best clinical judgment in advising patients.
There are both natural and artificial sources of UVR. Although there are many artificial sources of this energy, sunlight is the only natural source.
The sun emits a wide variety of electromagnetic radiation, including infrared, visible, ultraviolet A (UVA; 320 to 400 nm), ultraviolet B (UVB; 290 to 320 nm), and ultraviolet C (UVC; 10 to 290 nm). The only UVR wavelengths that reach the Earth's surface are UVA and UVB. UVA radiation is 1,000-fold less effective than UVB in producing skin redness. However, its predominance in the solar energy reaching the Earth's surface (tenfold to one hundredfold more than UVB) permits UVA to play a far more important role in contributing to the harmful effects of sun exposure than previously suspected.
Sunlight is the greatest source of human UVR exposure, affecting virtually everyone. The extent of an individual's exposure, however, varies widely depending on a multiplicity of factors such as clothing, occupation, lifestyle, age, and geographic factors such as altitude and latitude. There is greater UVR exposure with decreasing latitude. Residing at higher altitude results in a greater UVR exposure such that for every 1,000 feet above sea level, there is a compounded 4 percent increase in UVR exposure. UVR exposure increases with decreased stratospheric ozone. Other factors that influence exposure to UVR include heat, wind, humidity, pollutants, cloud cover, snow, season, and time of day.
Solar flares (sunspots) also alter the amount of UVR reaching the Earth. Solar flares increase ozone concentration in the stratosphere (above 50 km) thereby reducing the amount of surface UVB. This 11-year cycle of solar flares causes as much as a 400-percent variation in UVB at 300 nm reaching the earth. When solar flares are inactive, there is a decrease in the ozone concentration, allowing increased UVB to penetrate to the Earth's surface.
There is also serious concern about depletion of stratospheric ozone by manmade chlorofluorocarbons (CFC). These extraordinarily inert chemicals are used in numerous commercial products, including aerosols and refrigerants. The U.S. Environmental Protection Agency has been charged with estimating the effects on health associated with changes in stratospheric ozone levels. In a recent risk assessment document, the Agency predicted that without controls on CFC production, there would be a 40 percent depletion of ozone by the year 2075. The Agency further concluded that for every 1 percent decrease in ozone, there will be a compounded 2 percent increase in the more damaging shorter UVB wavelengths reaching the Earth's surface. Such an increase in UVB penetration to the earth is predicted to result in an additional 1 to 3 percent increase per year in nonmelanoma skin cancer (NMSC).
Recent satellite measurements already indicate a worldwide decrease in stratospheric ozone over the last decade. Both satellite- and land-based measurements have revealed a seasonal hole in the ozone layer over the Antarctic secondary to its destruction by CFC's. Although increased surface UVB has been measured in the Antarctic, there has not yet been a measurable change in UVB as a consequence of CFC's in the stratosphere in the United States.