EFFECTS OF UV RADIATION ON HUMAN HEALTH

A statement by the National Radiological Protection Board

The National Radiological Protection Board was established by the Radiological Protection Act 1970, and is responsible for conducting research and providing advice and services for protection against ionising and non-ionising radiations.

National Radiological Protection Board

Chairman:
Sir Keith Peters FRS
Director:
Professor R H Clarke
Secretary:
M C O'Riordan
Members:
Professor A D Baddeley FRS
Professor E H Grant
Professor D G Harnden
Professor J M Harrington CBE
Professor R M MacKie
Hon Mrs S Morrison
Professor G M Roberts
Dr M F Spittle

Introduction

This statement by the National Radiological Protection Board first appeared in Documents of the NRPB, 6, No. 2, 1-6 (1995), together with the report by the Advisory Group on Non-ionising Radiation on health effects from ultraviolet radiation.

Scope

The National Radiological Protection Board has a statutory responsibility to provide advice and information on standards of protection for exposure to non-ionising radiation. This includes the health effects and hazards associated with exposure to ultraviolet radiation (UVR). UVR is divided by wavelength into UVA 315-400 nrn, UVB 280-315 nm, and UVC 100-280 nm. Blue light lies in the range of about 400-500 nm.

In 1990, the director of the board set up an advisory group on non-ionising radiation "to review work on the biological effects of non-ionising radiation relevant to human health and to advise on research priorities".

In its third report, the advisory group has reviewed health effects from UVR(1). It has considered both natural and artificial sources of exposure, as well as experimental studies relevant to understanding the effects of UVR on cells and tissues. It has examined information on the clinical effects of UVR, and the results of epidemiological studies, with the aim of providing advice on the risks of exposure. Some information is also given on the effects of blue light.

The advisory group has also made recommendations for further research, aimed both at improving the basis for assessing exposures to natural and artificial sources, as well as furthering knowledge of the effects of UVR on health through experimental and epidemiological studies.

This statement by the board reviews the main conclusions of the advisory group. It also gives advice relevant to the protection of human health. It applies both to members of the public and to those who are occupationally exposed, and is intended to provide a framework for reducing UVR exposure and increasing awareness of its effects.

Sources

The main source of UVR contributing to personal exposure is the sun, and the major task is associated with personal habits in relation to solar radiation. For some individuals, however, UVR from artificial sources could contribute significantly to their total exposure. Such sources of exposure include sunbeds used for cosmetic tanning, a few in industry, and those used for medical therapy.

Effects

It is widely accepted that UVR is carcinogenic, and produces other undesirable health effects. The main tissues affected are those in the skin and the eye. There is evidence that UVR can also induce changes in the immune system, but the significance of this to human beings is not yet clear.

Skin

The most serious health effects, for which exposure to UVR is a recognised risk factor, are the cutaneous malignancies (skin cancers). UVB has been recognised for some time as carcinogenic in experimental animals, and there is increasing evidence that UVA, which penetrates more deeply into the skin, also contributes to the induction of cancer. UVC from the sun is absorbed by the earth's atmosphere, and any arising from artificial sources does not readily penetrate to the sensitive basal layer of the skin.

Short-term effects

Short-term effects on the skin may be seen as sunburn, principally consisting of erythema (skin reddening resulting from vasodilation) and oedema (swelling), both of which may be very severe. In some people this sunburn is followed by increased production of melanin, and is recognised as a suntan. Racially determined skin pigmentation will provide some protection. A suntan is not an indication of good health, and only offers minimal protection against further exposure. It is a sign that damaged skin is attempting to protect itself from further harm.(2,3)

Long-term effects

The most serious long-term effect is the induction of cancer. The non-melanoma skin cancers (NMSCs) are mainly basal cell carcinomas and squamous cell carcinomas. They are relatively common in white populations, although they are rarely fatal. The overall incidence is difficult to assess because of under-reporting. Reported NMSCs account for just over 5% of registered malignancies in the UK, but under 0.5% of cancer deaths. These rates are increasing year on year. They occur most frequently on sun-exposed areas of the body (such as the face and hands) and show an increasing incidence with increasing age. The findings from epidemiological studies indicate that the risk of both of these skin cancers can be related to cumulative UVR exposure, although the evidence is stronger for squamous cell carcinomas. UVR induces NMSCs in experimental animals.

Malignant melanoma is the main cause of skin cancer death, particularly in young people, although its incidence is less than NMSC. The risk of developing malignant melanoma has increased substantially in white populations for several decades, and the annual incidence in the UK is now approaching 10 new cases per 100,000 population (more than double the rate 15 years ago).

Occurring at relatively young ages, it is the cause of 1 in 12 cancers at ages 20-39 years, and 1 in 25 cancer deaths at these ages. A higher incidence is found in people with large numbers of naevi (moles), those with atypical naevi, those with a fair skin, red or blond hair, and those with a tendency to freckle, to sunburn, and not to tan on sun exposure. Both acute burning episodes of sun exposure and chronic occupational and recreational exposure probably contribute to the risk of malignant melanoma. There are indications that excessive sun exposure within the first two decades of life increases the risk of malignant melanoma later in life, although the precise nature of the relationship is still uncertain.

Chronic exposure to solar radiation causes photoageing of the skin which is characterised by a leathery, wrinkled appearance and loss of elasticity. Corroborating evidence for a role of UVR in the aetiology of these responses has been produced from extensive biological studies.

A small quantity of UVR is beneficial in terms of vitamin D synthesis in the skin. Whilst this may be important for those of the population on a restricted diet, for the great majority the deleterious effects of UVR in terms of cutaneous damage and increased risk of skin cancer are far more important.

Eye

Responses of the human eye to acute UVR exposure include photokeratitis and photoconjunctivitis (inflammation of the cornea and the conjunctiva, respectively). Repeated exposure is also considered to be a major factor in the causation of non-malignant clinical lesions of the cornea and conjunctiva, such as climatic droplet degeneration (discrete areas of yellow protein deposits in the cornea), pterygium (an overgrowth of the conjunctiva on to the cornea) and, probably, pinguecula (small yellow growths in the conjunctiva).

Epidemiological data on cataract formation in highly exposed people suggest that cumulative UVR exposure is a principal causative factor in the development of, at least, cortical cataracts, although the extent to which this is an important risk factor for cataracts in the general population is unclear. Few appropriate animal studies have been carried out, although acute exposures to UVB at levels above the threshold for photokeratitis have induced anterior cortical opacities.

There is good evidence that prolonged gazing at very bright light sources, particularly those emitting shorter wavelength blue light, causes retinal damage resulting in transient or permanent loss of visual acuity. Such an effect would normally be prevented by the natural aversion response invoked by looking at a bright light, but this response can be intentionally suppressed. Similar damage has also been induced in the non-human primate retina following acute exposure; blue light was the most effective. It is not clear to what extent UVA is involved. Transmission through the lens is low in adults, but is higher in children and in people who have had their lens surgically removed and have not had a suitable UVR-absorbing replacement lens fitted.

There is some equivocal evidence that chronic exposure to high levels of solar radiation is a contributory factor in the development of age-related macular degeneration of the retina, a major cause of blindness. There is insufficient evidence of an association between exposure of the eye to UVR and an increase in the risk of ocular melanoma.

Immune responses

Biological studies have shown that exposure to UVR can suppress the normal antigen-specific immune response to some skin tumours and to various skin pathogens, although immunity acquired from prior infection is not affected. The significance for human health of UVR-induced immune suppression is not clearly established at present, nor is the relationship between exposure to UVR and skin cancer in patients who are immunologically suppressed (e.g. following tissue transplants).

Recommendations

The board welcomes and supports the initiatives that have been taken forward by the government, and the Health Education Authority (4) and other agencies over the past few years in pursuance of The Health of the Nation (5) target to halt the year-on-year increase in skin cancer by 2005. The actions taken so far are consistent with the recommendations outlined below, which are intended to be applied to the population as a whole. Particular care is needed, however, for children and young people and others at greater risk of UVR-induced skin cancer, such as those with large numbers of naevi.

Public awareness

The board recommends strongly that educational programmes continue to aim at increasing awareness of the health effects of UVR exposure by the general public, and by those who may be occupationally exposed. This is particularly important for parents, those working in nurseries, school teachers, and others responsible for the day-to-day care of children. The objectives are to improve knowledge, influence attitudes, and change behaviour in relation to UVR exposure. The programmes should aim at a reduction in both the cumulative exposure to UVR and, particularly, exposure to high levels resulting in acute damage to the skin or eyes. The overall objective is a reduction in morbidity and mortality due to skin cancer.

Information relating to early diagnosis of skin cancer should be readily available to the public. The major signs of suspected malignant melanoma are:

• an existing mole getting larger
• an existing mole developing an irregular outline
• an existing mole showing mixed shades of brown and black
• a new mole growing quickly (in months)

Minor signs include a mole:

• becoming bigger than the blunt end of a pencil (around 5 mm)
• becoming inflamed or developing a reddish edge
• bleeding, oozing or crusting
• starting to feel different (e.g. itching or painful)

With the aim of increasing public awareness of current levels of UVR exposure throughout the country, the board supports the regular publication of levels of solar radiation. These measurements will also provide a basis for more realistic exposure assessments.

Clinical diagnosis of malignancy

Early detection of malignant melanomas is needed in order to reduce the present high mortality rate. Rapid referral to a medical practitioner is indicated if one or more of the major signs above are observed. Referral to a dermatology specialist should be considered if three or four minor signs are observed, even without the presence of a major sign.(6)

The board recommends that those concerned with education and training of medical practitioners, and other health-related professionals, should consider how to increase skills in the recognition and treatment of skin cancer. This would complement the anticipated improved public awareness, and enhance early diagnosis and effective treatment.

Protection from solar radiation and artificially produced UVR

Protection of the skin and eyes can be enhanced by wearing hats and clothing, wearing sunglasses which exclude UVR, and applying sunscreens. However, sunscreens are used to provide protection against sunburn. The protection against melanoma provided by the use of sunscreens is unclear, possibly because use may lead to longer and more intense exposure. Such protection is less certain than that provided by reducing exposure. The board recommends that standards organisations and manufacturers develop suitable and scientifically valid protection criteria for all these products, which should be agreed internationally. This would enable the public to understand each protection measure and use them effectively.

The board recognises the need for advice limiting exposure to UVR in the workplace. The initiative by the Health and Safety Executive in this area related to outdoor workers is strongly supported. (7)

The board recommends that the use of sunbeds and sunlamps for cosmetic tanning should be discouraged. Modern artificial tanning devices use predominantly UVA. However, since the spectra for biological damage extend into the UVA region, exposure to UVR from sunbeds and sunlamps is likely to carry a risk.

Some prescribed medicines, drugs, cosmetics, and various plant materials can cause sensitisation of the skin and eyes to UVR. The board recommends that patients and the general public should be warned by health professionals and manufacturers of these interactions with UVR.

Approaches to be considered in educational and awareness programmes for protection from solar radiation are given below.

Approaches to minimising sun-induced skin and eye damage

Remember that there is no such thing as a safe or healthy tan. Take sensible precautions to avoid sunburn, particularly in children.

Limit unprotected personal exposure to solar radiation, particularly during the four hours around noon, even in the UK. Seek shade wherever possible, but remember sunburn can occur even when in partial shade or when cloudy.

Remember that sunburn can occur while swimming, and is more likely when there is a high level of reflected UVF, such as from snow and sand.

Wear suitable head wear, such as a wide-brimmed hat, to reduce exposure to the face, head and neck. Cover exposed skin with clothing giving good protection - examples are long-sleeved shirts and loose clothing with a close weave. Sunglasses should be designed to exclude both direct and peripheral exposure of the eye.

Apply sunblocks, or broadband sunscreens with high sun protection factors (an SPF around 15) to exposed or uncovered skin. Apply generously and reapply frequently. The sun protection factor (SPF) is the ratio of the UVR exposure to produce minimal erythema on a skin site protected by sunscreen, to the UVR exposure to produce a comparable erythema on unprotected skin. (8)

Remember that certain prescribed drugs medicines, cosmetics, and plant materials can make people more sensitive to sunlight.

Research

The board supports the recommendations for further research made by the advisory group. The board recommends that the current research programmes to establish the biological mechanisms and the risks of cancer induction from UVR exposure should be continued. A significant research challenge exists to improve the effectiveness of screening for malignant melanomas.

Development of formal guidance on UVR exposure

The board will develop formal guidance on UVR exposure appropriate to the UK population. This guidance will not apply to patients receiving UVR as part of medical treatment.

References

1. NRPB. Health effects from ultraviolet radiation. Report of an Advisory Group on Non-ionising Radiation. Doc. NFPB, 6. No. 2, 7-190 (1995).
2. CRC. Malignant melanoma. London Cancer Research Campaign, Fact Sheet 4.1 (1995).
3. UK Skin Cancer Prevention Working Party. Consensus statement. London, British Association of Dermatologists (1994).
4. HEA. "Sun Know How" campaign. London, Health Education Authority (1994).
5. DH (Department of Health). The Health of the Nation: A strategy for health in England. London. HMSO, Cmd. 1986 (1992).
6. CRC. Malignant melanoma - A guide to early detection. London Cancer Research Campaign (1989).
7. HSE. "Keep Your Top On". London Health and Safety Executive, (IND CG) 147L (1995).
8. CIE. Sunscreen testing (UVB). Vienna. International Commission on Illumination, Technical Report CIE 90 (1991).