Sun Exposure


Being tan has not always been thought of as the aesthetic ideal, but in our current culture many people seek a "healthy tan," There are some benefits to modest sun exposure, but there is clear evidence that overexposure to ultraviolet radiation in sunlight can have a number of adverse health effects. This module will provide background on the history of tanning and the related health risks.


Learning Objectives

After successfully completing this module, you will be able to:

The Rising Sun - Evolution of the Concept of the "Healthy Tan"

Our current culture largely views tanned skin as healthy and attractive, but this has not always been the case. The Romans and Greeks valued pale skin and used cosmetics to whiten their skin. Pale skin was also the fashion in Elizabethan England, where bronze skin indicated a working class person who toiled in the sun. The Industrial Revolution diminished this distinction, however, as workers moved from the country to the cities, and large numbers of them began working in factories, Perceptions about the effect of sun on health also evolved. The absence of sun took a toll that was both psychological and physical. The working class lived in cramped buildings with small courtyards that blocked out the sun, and the enormous increase in coal burning during the Industrial Revolution generated clouds of soot that blocked the sunlight and contributed to the development of rickets in children. The link between insufficient sunlight and rickets was recognized as early as 1822. Then, evidence began to emerge regarding the benefits of sunlight. In 1903 Dr. Auguste Rollier opened a clinic in the Swiss alps that offered sunlight and fresh air to patients with tuberculosis. During the same year Dr. Niels Ryburg Finsen was awarded the Nobel Prize for using artificial sunlight to treat tuberculosis of the skin. French designer Coco Chanel allegedly contributed to the concept that tan is beautiful after acquiring a tan during a vacation on a yacht in 1923. Sunbathing became increasingly popular in Britain in the 1920s. In order to prevent rickets, the US government began making recommendations about sun exposure in the the 1930s, and milk began to be fortified with vitamin D during the same decade. The introduction of the bikini in the 1950s further fueled the popularity of sunbathing. By 1968 about 58% of young adults believed that a tan improved appearance, and by 2007 this view was held by 81%. In the 1980s tanning salons began to spring up, and they have become increasingly popular; the tanning industry claims that tanning salons are now used by as much as 10% of the US population. In fact, some studies suggest that tanning may be addictive, perhaps as a result of beta-endorphins that are generated in the skin during tanning. Exposure to sunlight also initiates biochemical reactions in skin that lead to the generation of vitamin D, which has beneficial effects on health. However, a number of studies have documented an alarming increase in the incidence of melanoma, a highly dangerous form of skin cancer, over the past few decades. Because of the health benefits of vitamin D, some have tried to frame the issue of tanning as a controversy. However, if one critically considers the evidence, there is compelling evidence that we should limit our exposure very carefully.


Ultraviolet Radiation

The health effects of both natural and artificial sunlight are the result of exposure to ultraviolet (UV) radiation. Ultraviolet (UV) light is part of the electromagnetic radiation that reaches the earth from the sun. UV radiation has shorter, more energetic wavelengths (400-100 nm) than visible light (750-400 nm).


UV radiation is further categorized as UV-A, UV-B, and UV-C. The earth's ozone layer filters out all of the sun's UV-C and most of the UV-B. However, much of the UV-A and some UV-B reach the earth. All three types of UV can be generated by man-made devices, and all three can have harmful effects. UV-A and UV-B are generated from tanning beds and lights, and UV-C, which is particularly dangerous, is generated by germicidal lamps. The World Health Organization has web pages (in six languages) with succinct summaries of environmental factors that influence our exposure, health effects of ultraviolet radiation, and protective measures. They also provide a link to information about WHO's INTERSUN Program, which strives to provide education about UV exposure and to promote measures that reduce the harmful effects of UV. They also provide a publication entitled "Artificial Tanning Sunbeds: Risk and Guidance," with a number of very specific recommendations that would be relevant to local boards of health and health departments.

It is important to note that UV emitted from artificial sources varies greatly in terms of both the amount of light emitted and the specific wavelengths of UV, which can in turn result in more serious health effects.

UV Type

Wavelength (nm)


UV-A (near UV)


UV-A is less damaging than UV-B, but the effects are largely the same.

UV-B (mid UV)


  • Promotes synthesis of vitamin D precursors in skin.
  • Causes photochemical damage to cellular DNA.
  • Tanning
  • Erythema (sunburn)
  • Cataracts
  • Skin cancer
  • Suppression of immune system

UV-C (far UV)


  • Corneal burns
  • Severe skin burning


 The UV Index

The UV Index, developed by the National Weather Service and EPA, indicates the strength of solar UV radiation on a scale from 1 (low) to 11+ (extremely high). The scale provides a means of gauging appropriate precautions in order to avoid overexposure to UV radiation.



The US Environmental Protection Agency's SunWise Program explains the UV Index and provides several valuable resources for local health departments. These include:

  1. A UV Index map of the United States that gives 1, 2, 3, and 4-day forecasts of the UV Index.
  2. A UV Index Alert
  3. "Apps" that can be installed on your smart phone in order to look up UV Index information.
  4. A UV Index "look-up function. You enter your local zip code, and it looks up your current index. There is also a 'widget' that enables you to add the function to your own web page, as shown here:

Artificial Sources of Ultraviolet Radiation

In addition to the UV radiation from the sun, there are many man-made sources of UV. These include:

Ultraviolet light exposure affords us some potential benefits, but also substantial risks of skin cancer, photo-aging of skin, and burning. The next section will but these potential risks and benefits into perspective.


Harmful Effects of Ultraviolet Radiation

EPA's Summary of Harmful Effects of Over Exposure to UV

A video excerpt from the TV documentary "The Universe":

Also see an online article in which Dr. Barbara Gilchrist, a dermatologist at Boston University Medical Center, discusses the harmful effects of tanning, particularly in young people. Link to BU Today article

Eye Injuries Associated with Tanning

Permanent eye injuries can result from acute and chronic exposure to either natural or artificial sunlight. It is important to note that closed eyelids are not an adequate means of protection, since they only block about 25% of UV rays.


Potential injuries include:

A short video from Info4YourLife

Skin Types

The extent of damage after exposure to UV radiation is dependent on many factors such as duration, frequency, time of year, cloud cover, use of sun block, etc. However, another factor that is important is the type of skin. The table below shows the six widely recognized skin types. These should be taken into account by operators in tanning salons when determining maximum exposures. For a PowerPoint slide show on skin types, open this link.

Type I: Highly sun-sensitive, always burns, never tans.
Example: Very pale Caucasian, freckles, or Albino
Type II: Very sun-sensitive, burns easily, tans minimally.
Example: Fair-skinned Caucasian
Type III: Sun-sensitive skin, sometimes burns, slowly tans to light brown.
Example: Darker Caucasian, European mix
Type IV: Minimally sun-sensitive, rarely burns, always tans to moderate brown.
Example: Mediterranean, European, Asian, Hispanic, Native American
Type V: Sun-insensitive skin, rarely burns, tans well.
Example: Hispanic, Afro-American, Middle Eastern
Type VI: Sun-insensitive, never burns, deeply pigmented.
Example: Afro-American, African, Middle Eastern





Skin Cancer

Ultraviolet radiation penetrates the superficial layers of the skin, and its energy is absorbed by the nucleotides of DNA. This can cause abnormalities in the structure of DNA that result in mutations that interfere with regulation of cell division. For example, p53 is a tumor suppressor that has been found to be rendered inoperable because of mutations in about 50% of skin cancers. UV light is the most significant source of mutagenic non-ionizing radiation and is responsible for most skin cancers.

Melanomas and Basal/Squamous

The National Institutes of Health (NIH) has a good web site providing an array of information about sun damage and skin cancer. See NIH Senior Health.

Identifying Skin Cancers: Click on the Photo Album Activity below to see a rogues gallery of skin cancers.



Identifying Skin Cancers

(Length: 6:46)

Basal Cell Carcinoma

From Memorial Sloan-Kettering Cancer Center (3:00):

Squamous Cell Carcinoma

From Memorial Sloan-Kettering Cancer Center (3:11)



From Memorial Sloan-Kettering Cancer Center (1 minute)


Pre-Cancerous Skin Lesions

From Memorial Sloan-Kettering Cancer Center (1:05)



Ten Tips on How to Avoid Skin Cancer

From Memorial Sloan-Kettering Cancer Center (3:08)


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ABDEs of skin cancer detection handout


Preventing the Harmful Effects of Ultraviolet Radiation

Sun Protection Factor (SPF)

Sunscreens provide partial protection from ultraviolet rays, but they vary in their ability to block UVA and UVB rays. Products vary in their composition, but in general, they contain chemicals that absorb, reflect, or scatter light. Reddening and burning of the skin has been attributed primarily to UVB rays, while UVA penetrates deeper and is thought to be more responsible for photoaging and skin cancer. Nevertheless, the effects of UVA and UVB are largely the same, and products vary in their ability to block UVA and UVB.

A sunscreen's effectiveness is commonly measured by its sun protection factor, or SPF. SPF is not an amount of protection per se. It indicates how long it will take for UVB rays to redden skin when using a sunscreen, compared to how long skin would take to redden without the product. For instance, someone using a sunscreen with an SPF of 15 will take 15 times longer to redden than without the sunscreen. An SPF 15 sunscreen screens 93 percent of the sun's UVB rays; SPF 30 protects against 97 percent; and SPF 50, 98 percent. The Skin Cancer Foundation maintains that SPFs of 15 or higher are necessary for adequate protection.

Sunscreen wears off with time, and its efficacy diminishes substantially with swimming or when perspiring. Consequently, it is important to reapply it at least every two hours and more frequently if you are swimming or sweating.

0_61_sunscreen.jpg spf_vs_uvb_protection.gif


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Resources and Programs to Promote Prevention

The US Environmental Protection Agency (EPA) has an informative web page as part of their Sunwise Program that provides an overview of various harmful effects of excessive sun exposure. This page also provides links that explain the UV Index, how the index is calculated, and a UV Index Widget that tells you the UV Index in your ZIP code. The SunWise Program also has value links that provide information for schools and educators, for kids, and for communities, and their is information in Spanish as well.

An online video Public Service Announcement that provides an engaging message for the general public can be found here. (Created by students at Boston University School of Public Health.)

This link is to an article on sun safety written for the Watertown Health Department. It is an illustration of the kind of public service information that might be sent to local newspapers. The article was written by Ramya Kumar, an MPH candidate at Boston University School of Public Health.

Vitamin D and Bone Health

vitamind_conversion.gif Vitamin D promotes absorption of dietary calcium from the intestine and plays an important role in regulating calcium deposition in our bones. Humans can derive vitamin D from dietary sources or from exposure to UV. Historically, humans have derived most of their vitamin D as a result of exposure to sunlight. Cells in our skin have a precursor for vitamin D synthesis, 7-dehydrocholesterol. Exposure to UV-B radiation (290–315 nm) causes a chemical change in 7-hydroxycholesterol that converts it to vitamin D3. Vitamin D from the skin or from dietary sources is then converted to 25-hydroxyvitamin D in the liver. This, in turn, is then converted into the active form of vitamin D is (1,25-dihydroxyvitamin D) primarily in the kidney.


Vitamin D promotes calcium absorption from the intestine and is essential to bone mineralization and maintenance of calcium and phosphate concentrations in blood. Without sufficient vitamin D and calcium bone mineralization is impaired, resulting in rickets in children and osteoporosis in adults. Dr. Michael Holick, an authority on vitamin D, published a succinct review of "Vitamin D Deficiency" in 2007 in the New England Journal of Medicine.



Dietary Sources of Vitamin D:

Relatively few foods have significant levels of vitamin D in nature. The best sources are fish, such as salmon, tuna, and mackerel and fish liver oils. Smaller amounts are found in beef liver, cheese, and egg yolks. Most of the dietary vitamin D in US comes from foods that have been fortified. For example, milk in the US is fortified with 100 IU per cup, and milk products and calcium-fortified fruit juices may also be fortified.An authoritative summary of the effects of vitamin D, the consequences of vitamin D deficiency and the human requirements for vitamin D can be obtained from the Dietary Supplement Fact Sheet on Vitamin D, published by the Office of Dietary Supplements from the National Institutes of Health.

Vitamin D from Sun Exposure

The amount of vitamin D generated by exposure to sunlight is affected by many factors including the season of the year, latitude, time of day, cloud cover, smog, number of hours spent outdoors, and usage of sunscreen. Latitudes greater then 42 degrees of latitude (e.g., north of California and Boston) do not provide enough UVB radiation to sustain vitamin D levels from November through February. UVB intensity that is sufficient to sustain vitamin D levels throughout the entire year only occurs below 34 degrees latitude (e.g., south of Los Angeles and Columbia, South Carolina). UVB is blocked by cloud cover, air pollution, glass, and sun screen lotions with SPF 8 or greater if applied in sufficient quantity.

Some vitamin D researchers have recommended sunlight or tanning bed exposure for 5-30 minutes several times a week as an alternative to dietary supplementation in northern latitudes during the winter. However, given the well-established causal role that UV radiation plays in skin cancer, this recommendation is controversial to say the least.


Vitamin D Requirements in Humans

In November 2010 the Institute of Medicine conducted an exhaustive review of the scientific findings regarding the effects of calcium and vitamin D on health. The IOM concluded:

"Scientific evidence indicates that calcium and vitamin D play key roles in bone health. The current evidence, however, does not support other benefits for vitamin D or calcium intake."


"Vitamin D levels in the body may come from not only vitamin D in the diet but also from synthesis in the skin through sunlight exposure. The amount of sun exposure one receives varies greatly from person to person, and people are advised against sun exposure to reduce the risk of skin cancer. Therefore, the committee assumed minimal sun exposure when establishing the DRIs for vitamin D, and it determined that North Americans need on average 400 International Units (IUs) of vitamin D per day (see table for the Recommended Dietary Allowances— values sufficient to meet the needs of virtually all persons). People age 71 and older may require as much as 800 IUs per day because of potential changes in people's bodies as they age."

"At this time, the scientific data available indicate a key role for calcium and vitamin D in skeletal health and provide a sound basis for DRIs. The data do not, however, provide compelling evidence that either nutrient is causally related to extra-skeletal health outcomes or that intakes greater than those established in the DRI process have benefits for health."

The IOM's specific recommendations for vitamin D intake are summarized in this table:


For a one-minute summary of the IOM committee's findings, see the video below.


Other Benefits of Vitamin D

Ecological studies have noted that populations living at higher latitudes have an increased risk of colon, breast, prostate and certain other cancers. Since people living at higher latitudes have less exposure to sunlight and lower production of vitamin D3, it was suggested that there may be an association between vitamin D deficiency and cancer. Prospective studies also found that adults with low blood levels of vitamin D had a 30-50% increased risk of breast, colon, pancreatic and other cancers. Moreover, additional studies indicate that dietary supplementation with vitamin D is associated with a decreased risk of cancer. Less convincing studies suggest that vitamin D may decrease the risk of depression, eclampsia in pregnancy, and type I diabetes. Michael Holick, PhD, MD at Boston University Medical Center, an endocrinologist who has published many studies on vitamin D. Two of his review articles summarize evidence for the potential benefits of vitamin D. See:

  1. Holick MF: Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. American Journal of Clinical Nutrition, Vol. 80, No. 6, 1678S-1688S, December 2004
  2. Holick MF and Chen TC: Assessment of Vitamin D in Population-Based Studies: Vitamin D deficiency: a worldwide problem with health consequences. American Journal of Clinical Nutrition, Vol. 87, No. 4, 1080S-1086S, April 2008






There is strong evidence for the benefits of vitamin D to ensure bone health, but as noted in the IOM report, there is insufficient evidence to support these other claims at the present time.

Medical Uses of Ultraviolet Radiation (UV)

UV may be used in medical applications, but general exposure to sunlight or tanning devices should not be used as a replacement for actual medical care. Examples where phototherapy can be useful in treating several conditions, include

Is There a Controversy?

The following is an excerpt from Dr. Barbara Gilchrest's article entitled "Sun exposure and vitamin D sufficiency".Am J Clin Nutr 2008;88(suppl):570S–7S.


The Indoor Tanning Industry

"In the United States alone, the indoor tanning business earns $5 billion per year (51, 52) and has >50 000 tanning facilities, 28 million customers annually (53), and >1 million visits per day. In some regions of the United States, more than half of all teenage girls have visited a tanning facility at least 3 times in the previous year. Because professional groups such as the American Academy of Dermatology have requested stricter guidelines and better enforcement of existing regulations governing indoor tanning, over the past decade, at least 29 states have enacted legislation restricting access to tanning parlors for teenagers,and at least 3 additional states are considering similar legislation .... The indoor tanning industry vigorously opposes such legislation through paid lobbyists and a well-orchestrated media campaign. The cornerstone of the industry's argument to curtail proposed restrictions on teenage use and general overuse is that more UV exposure is healthy, indoor tanning is safer than natural tanning, and UV radiation exposure reduces the risk of multiple diseases. The message that the tanning industry has shared with state legislatures and the media and that the UV Foundation's web site publicizes is: 'Vitamin D from UV exposure is free and easy to get—why pass up the simplest way to improve your odds of preventing cancer?' "



Informed Consumer Guide to Indoor Tanning

Consumer Update from the US Food and Drug Administration


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American Tanning Institute, Indoor Tanning Certification

Massachusetts Department of Public Health (MDPH), Radiation Control Program

Environmental Protection Agency (EPA), Sunwise Program

Florida Department of Health, Tanning Information & Resources

Food & Drug Administration (FDA), Indoor Tanning: The Risks of Ultraviolet Rays

National Institutes of Health (NIH) SeniorHealth, Skin Cancer

Howard County Health Department,Tanning Facilities Program

World Health Organization (WHO), Ultraviolet radiation and the INTERSUN Programme