Documents of the NRPB: Volume 13, No. 1
Health Effects from Ultraviolet Radiation: Report of an Advisory Group on Non-Ionising Radiation
- 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 radiation in the range of wavelengths 100-400 nm. It is divided by wavelength into UVA 315-400 nm, UVB 280-315 nm and UVC 100-280 nm. Blue light lies in the range of about 400-500 nm.
- The Board's Advisory Group on Non-Ionising Radiation has a remit:
to review work on the biological effects of non-ionising radiation relevant to human health and to advise on research priorities
- In this, its seventh report, the Advisory Group has updated its previous review of the health effects from UVR (NRPB, 1995). 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 health effects of exposure. The Advisory Group has also made recommendations for further research aimed 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 summary reviews the main conclusions of the Advisory Group. At the specific request of the Board it also gives advice on the means of protection of human health. This applies both to members of the public and to those who are occupationally exposed and is intended to provide a practical basis for reducing UVR exposure and increasing awareness of its effects.
- For most people, the main source of UVR exposure is the sun, but for some individuals substantial exposures occur from artificial sources including sunbeds used for cosmetic tanning, industrial lamps, arc welding, and medical UVR therapies.
- There is convincing evidence that UVR can cause damage to DNA and in animal experiments it has been shown to be a cause of cancer. The International Agency for Research in Cancer (IARC) has concluded that solar radiation, broad spectrum UVR, and UVA, UVB or UVC radiation are all carcinogenic to experimental animals (IARC, 1992). Exposure to UVR also increases the risk of skin cancer in man and produces other undesirable health effects. The main tissues of the human body affected are those of the skin and the eye. There are also effects on the immune system, the significance of which for human health is not yet clear. The principal known beneficial effect of UVR exposure is its role in the production of vitamin D in the skin.
- The most serious adverse 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.
- Excessive short-term exposure of the skin causes sunburn, principally consisting of erythema (skin reddening resulting from vasodilation) and oedema (swelling), both of which may be very severe. In some people sun exposure is followed by increased production of melanin and is recognised as a suntan. Genetically determined skin pigmentation will provide some protection against sunburn. A suntan offers only limited protection against further exposure and is not an indication of good health (CRC, 1989; UK Skin Cancer Prevention Working Party, 1994).
- Excess sun exposure can increase the risk of both non-melanoma and melanoma skin cancers, the latter being the main cause of skin cancer death. Skin cancers cause about 2000 deaths each year in Britain, which is about 1.4% of all cancer deaths. 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 about 15% of registered malignancies in the UK, but only around 0.3% of cancer deaths. Incidence rates of these tumours have increased in white populations progressively for many years. They occur most frequently on sun-exposed areas of the body such as the face and hands and their incidence increases with age. Risks are greatest in people with fair complexions (light skin, red or blond hair, and blue eyes) and sun-sensitive skins. 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 than basal 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 that of NMSC. It is responsible for about 80% of skin cancer deaths. The risk of developing malignant melanoma has increased substantially in white populations for several decades and the annual incidence in the UK now approaches about 10 new cases per 100 000 population; more than double the rate 20 years ago. Melanoma mortality has, however, levelled off or even fallen in recent birth cohorts. Melanomas commonly occur at relatively young ages; at ages 20-39 years they account for about 1 in 11 of all cancers and about 1 in 20 of all cancer deaths. A raised incidence is found in association with large numbers of naevi (moles), with atypical naevi, with a fair skin and red or blond hair, and with a tendency to freckle and burn and not tan on exposure to the sun. There is evidence that short, intense exposures of the type arising from sunbathing are important in the causation of melanoma, but chronic cumulative exposures may also be relevant. Childhood exposures may be particularly important.
- Sunscreens will protect against sunburn and there is evidence from trials that they can reduce the risk of squamous cell carcinoma. Overall, however, it is unclear how effective sunscreens are at protecting against skin cancers, especially melanoma.
- Although it has not been established directly whether sunbeds cause skin cancer, they are an appreciable source of intense, intermittent UVR exposure and as such represent a potential health risk.
- 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 changes has been produced from extensive biological studies.
- Certain individuals have abnormal skin responses to UVR exposure ('photosensitivity') because of genetic, metabolic or other abnormalities, or show photosensitive responses because of intake or contact with certain drugs or other chemicals.
- The main known benefit of UVR exposure is the generation of vitamin D, which can be synthesised in the skin and is essential for healthy bone growth and maintenance. Dietary intakes of vitamin D are often low in the UK population, but short periods outdoors, as normally occur in everyday life, will produce sufficient vitamin D, and additional or intensive exposures will not confer further benefit. Research is ongoing into the possibility that dietary factors may affect risks of UVR-associated skin cancer, but this is not yet established.
- Pathological responses of the human eye to excessive UVR exposure include photokeratitis and photoconjunctivitis (inflammation of the cornea and the conjunctiva, respectively). Repeated exposure is 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 and conjunctiva), pterygium (an overgrowth of the conjunctiva on to the cornea) and, probably, pinguecula (small yellow growths in the conjunctiva). Damage can result from exposure to UVA, UVB and UVC.
- There is epidemiological evidence that chronic exposure of the eye to intense levels of UVR contributes to the development of cortical cataract. Evidence for a causal role of solar radiation in macular degeneration (a major cause of blindness) is conflicting. The extent to which UVR exposure is an important risk factor for cataracts in the general population is unclear, as is its relation to eye melanoma.
- 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. Staring at the sun can damage the retina permanently. 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, particularly to blue light. It is not clear to what extent UVA is involved as its transmission through the lens is low in adults but is higher in children.
- There is experimental evidence in animal models and human subjects of suppressive effects of UVR on the immune system. Biological studies have shown that exposure to UVR can suppress the normal antigen-specific immune response to some skin tumours and to various pathogens. The significance for human health of UVR-induced immune suppression is not, however, clearly established at present.
- A link has been demonstrated between sun exposure and the reappearance of the symptoms of herpes simplex virus (cold sores) in a proportion of latently infected individuals. In addition, there is a risk of converting benign papillomas caused by various human papillomavirus types, to squamous cell carcinomas in immuno-compromised subjects in areas of the skin that are normally exposed to the sun.
Non-Hodgkin's lymphoma (NHL)
- Overall, the data are not consistent with a major role for solar UVR in the aetiology of non-Hodgkin's lymphoma (NHL), but they leave open the possibility of a minor role, or an aetiological relation for a particular subtype of the disease.
- There is a need for public health advice on limiting exposure to UVR. Provision of information to the population as a whole about the risks of exposure is important. UVR can cause skin damage in people of all skin colours, although fair skins are more sensitive. Eye damage can occur in all populations. Particular care is desirable in children and young people, people with large numbers of naevi and those with fair complexions (light skin, red or blonde hair and blue eyes) and sun-sensitive skins.
Awareness of UVR risks
- Educational programmes should continue to aim at increasing awareness of the health effects of UVR exposure. 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 to reduce the cumulative exposure to UVR and, particularly, exposure to high levels resulting in acute damage to the skin and/or eyes. In this context, national and international initiatives such as the development of the Global Solar UV Index (as an indication of exposure) and campaigns by the World Health Organization are important.
- Information relating to early diagnosis of skin cancer should be readily available to the public.
- There is a need to continue to measure the levels of solar UVR throughout the country and to publish these data regularly. The measurements by NRPB provide a basis for realistic exposure assessments.
Protection from solar and artificially produced UVR
- The skin can be protected by wearing hats and clothing and by applying sunscreens. However, sunscreens should not be used to intentionally prolong exposure. Protection by sunscreens is less certain than that provided by reducing exposure. The continued development and use of suitable and scientifically valid protection criteria for clothing and other protective products is desirable, as is the development of internationally agreed standards.
- The eyes can be protected by wearing a hat, eye shades and using sunglasses that exclude both direct and reflected UVR. It is important that these incorporate wrap-around protection. Sunglasses fitted with small lenses offer inadequate protection and may actually increase risk of eye damage as they can cause dilation of the pupils and allow the entry of more UVR into the eye from around the periphery of the sunglasses.
- There is a need for advice limiting exposure to UVR at work, both indoors and outdoors. The Health and Safety Executive has issued advice to outdoor workers and their employers (HSE, 2001).
- The Advisory Group recommends that the use of sunbeds and sunlamps for cosmetic tanning should be discouraged.
- Some prescribed medicines, drugs, foods, cosmetics and various plant materials can cause sensitisation of the skin and eyes to UVR. 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 UVR are given in the table.
Approaches to minimising UVR-induced skin and eye damage
- Take sensible precautions to avoid sunburn, particularly in children.
- Remember that a suntan offers only modest protection against further exposure. It is not an indication of good health.
- Limit unprotected personal exposure to solar radiation, particularly during the four hours around midday, even in the UK.
- Seek shade, but remember sunburn can occur even when in partial shade or when cloudy.
- Remember that overexposure of skin and eyes can occur while swimming and is more likely when there is a high level of reflected UVR, such as from snow and sand.
- Wear suitable head wear, such as a wide-brimmed hat, to reduce exposure to the face, eyes, head and neck.
- Cover skin with clothing giving good protection - examples are long-sleeved shirts and loose clothing with a close weave.
- Sunglasses should exclude both direct and peripheral exposure of the eye to UVR, i.e. be of a wrap-around design.
- Apply sunblocks, or broad-band sunscreens with high sun protection factors (at least SPF151), to exposed skin. Apply generously and reapply frequently, especially after activities that remove them, such as swimming or towelling.
- Remember that certain individuals have abnormal skin responses to UVR exposure and may need medical help. Certain prescribed drugs, medicines, foods, cosmetics and plant materials can also make people more sensitive to sunlight.
- Areas in which research is needed include: the UVR outputs of artificial sources; the molecular basis of UVR cutaneous carcinogenesis in cellular systems and in animals; the immunological effects of UVR and their relevance to human health; the effects of UVR on risk of eye disease especially macular degeneration and choroidal malignancy; the relation of different types of UVR exposure to skin diseases including photodamage, photosensitivity disorders and skin cancers; the possible prevention of skin cancer by dietary factors; and the optimisation of UVR exposure in different situations for maintenance of adequate vitamin D status.
CIE (1991). Sunscreen testing (UVB). Vienna, International Commission on Illumination, Technical Report CIE 90.
CRC (1989). Malignant melanoma: A guide to early detection. London, Cancer Research Campaign.
FDA (Department of Health and Human Services of the US Food and Drug Administration) (1978). Sunscreen drug products for over the counter use: Proposed safety, effectiveness and labelling conditions. Federal Register, 43, No. 166, 38206-69.
HSE (2001). Sun protection, advice to employers of outdoor workers. London, Health and Safety Executive, INDG337 C2000.
IARC (1992). Monographs on the evaluation of carcinogenic risks to humans. Volume 55: Solar and ultraviolet radiation. Lyon, International Agency for Research on Cancer.
NRPB (1995). Health effects from ultraviolet radiation: Report of an Advisory Group on Non-Ionising Radiation. Doc NRPB, 6, No. 2 7-190.
UK Skin Cancer Prevention Working Party (1994). Consensus statement. London, British Association of Dermatologists.
Last reviewed: 13 October 2010