Ultraviolet Radiation

Primary reference(s)

WHO 2022a. Ultraviolet Radiation World Health Organisation (WHO). Accessed 24 February 2025

Annotations

Key relevant UN convention / multilateral treaty

The Montreal Protocol on Substances that Deplete the Ozone Layer (UNEP, 2010a, b). 

The UN Sustainable Development Goals (SDG)s, Goal 3 ‘Good Health and well Being’ (UNEP, 2020).

The United Nations Convention on the Rights of the Child (UN, 1989).

The United Nations Convention on the Rights of the Child (UN, 1989). 

Drivers

Exposure to sunlight occupationally or for leisure is a hazard driver. 

Impacts

Small amounts of UVR are essential to good health as it leads to the production of vitamin D in the body. Vitamin D strengthens the bone and musculoskeletal system. (WHO, 2022a). However, excessive exposure to UVR is associated with negative health consequences as UVR is carcinogenic to humans (WHO, 2022a). Skin cancer treatment costs exceed $8B annually in the U.S. (WHO, 2024).

Effects on the skin Acute effects of UVR include DNA damage, sunburn, phototoxic and photoallergic reactions, and suppression of the immune system. Immunosuppression can be considered as a risk factor for cancer and can cause reactivation of viruses (e.g. cold sores in the lip). 

Chronic effects on skin and lips from UVR exposure include: 

• cutaneous melanoma: a life-threatening malignant skin cancer;
• squamous cell carcinoma (SCC): a malignant cancer, which generally spreads less than melanoma and is less likely to cause death;
• basal cell carcinoma (BCC): a slow-growing skin cancer appearing predominantly in older people; and
• premature skin aging: a loss of skin elasticity at a young age with decreased wound healing.  

Excessive exposure to UVR caused around 1.2 million new cases of non-melanoma skin cancers (SCC and BCC) and 325 000 melanomas of the skin, and 64 000 premature deaths from non-melanoma and 57 000 melanomas of the skin in the year 2020 (WHO, 2022a; IARC, 2012). In the US, in the melanoma section of the skin statistics, data suggests that each year about 6.1 million adults are treated for basal cell and squamous cell carcinomas at a cost of about $8.9 billion (CDC, 2024). 

Effects on the eyes: acute effects of UVR include photokeratitis and photoconjunctivitis (inflammation of the cornea and conjunctiva, respectively). These effects are reversible, easily prevented by protective eyewear and are not usually associated with any long-term damage but are painful and might require therapeutic intervention. 

Chronic effects of UVR include: 

• cataract (an eye disease where the lens becomes increasingly opaque, resulting in impaired vision and eventual blindness);
• pterygium (growth of fleshy tissue which can cover part of the cornea); and
• cancer in and around the eye (basal cell carcinoma, squamous cell carcinoma and melanoma). 

UV exposure may also be involved in the development of age-related macular degeneration (AMD). 

Worldwide, it is estimated that 15 million people are blind due to cataracts; of these, some 10% may be due to exposure to UVR (WHO, 2022a). 

Multi-hazard context

UV radiation contributes to various environmental problems, such as photochemical smog formation, ozone depletion, and the degradation of pollutants and can exacerbate the impacts of other hazards such as the degradation of plastics in the environment (Menger et al, 2024), ocean warming and coral bleaching (UNEP, 2022).

Risk Management

The rise in the number of cases of skin cancer over the past decades is strongly related to increased exposure to the sun during outdoor activities and to artificial sources of UV radiation such as sunlamps and tanning beds. Overexposure is also the underlying cause of harmful effects on the eyes and immune system (WHO, 2014). 

Adopting a few simple precautions can greatly reduce the risk of these health conditions: 

• Limit time in the midday sun from 10 a.m. to 4 p.m., particularly on days when the UV index is high.
• When UV rays are most intense and you must be outside, try to find shade and wear protective clothing, including a brimmed hat that provides sun protection for your head, face and neck.
• Use a broad-spectrum sunscreen of at least 15 SPF – ideally higher– and reapply every 2 hours.
• Avoid sunlamps and tanning parlours, as they are known to damage the skin and eyes (WHO no date, WHO, 2024). 

Children and adolescents are particularly vulnerable to the harmful effects of UVR due to their skin and eye structure. Sunburns in childhood lead to a higher risk of skin cancer in later life. Also, a larger amount of UVR can reach and damage their retina (WHO 2022a). 

Fair-skinned people suffer more from sunburn and have a higher risk of skin cancer than dark-skinned people; however, darker-skinned people also develop skin cancers. Consideration of eye damage is important for everyone. People at increased risk include those with a high number of naevi, those taking photosensitizing medication, and those with a family history of skin cancer. Outdoor workers exposed occupationally to solar UVR levels face an increased risk of developing non-melanoma skin cancers (WHO 2022a). 

WHO works with Member States and partners to increase public understanding of the effects of overexposure to ultraviolet radiation (WHO no date). The INTERSUN Programme is a collaboration between WHO, the United Nations Environment Programme, the World Meteorological Organization, the International Agency on Cancer Research and the International Commission on Non-Ionizing Radiation Protection. It promotes and evaluates research on the health effects of UV radiation, and develops an appropriate response through guidelines, recommendations and information dissemination. The goals of the programme including providing practical and sound advice on the health and environmental impacts of UV exposure, encouraging countries to take action to reduce UV-induced health risks and provide guidance to national authorities about sun awareness programmes (WHO no date). To this end, the programme collaborates with experts and specialist agencies to implement key research activities, identifies and quantifies health risks from UV radiation, develops reliable predictions of health and environmental consequences of changes in UV exposure with stratospheric ozone depletion, and develops practical ways of monitoring change in UV-induced health effects over time. The programme provides tools and guidelines related to the UV index, sun protection for children, artificial sunbeds, tourism and occupational health (WHO no date).

Monitoring

A new app for mobile phones that provides localized information on ultraviolet (UV) radiation levels has been launched by the World Health Organization (WHO), the World Meteorological Organization (WMO), the United Nations Environment Programme (UNEP) and the International Labour Organization (ILO). The SunSmart Global UV app provides five-day UV and weather forecasts at searchable locations. It highlights time slots when sun protection is required with the aim of helping people around the world know when to use sun protection, in an effort to reduce the global burden of skin cancer and UV-related eye damage (WHO 2022 b).

The SunSmart Global UV app is available free of charge at both the Apple App and Google Play stores. It provides personalized options so that users can take actions to protect prolonged, excessive UV exposure, a major cause of skin cancer and other UV- related diseases. The app allows the inclusion of national and local data streams and adaptation to multiple languages - it is currently available in Chinese, English, French, German, Russian, Dutch and Spanish (WHO 2022 b).

The app is based on the UV Index, which describes the level of solar UV radiation at the earth's surface. The UV Index is reported on a scale of 1 (or "Low") to 11 and higher (or "Extreme"). The higher the index value, the greater the potential for damage to the skin and eye, and the less time it takes for harm to occur. The maximum UV Index is at the solar noon when the sun is highest in the sky. Adapting outdoor activities and using sun protection are recommended when the UV Index is 3 or above. UV damage is cumulative, and UV can be harmful when people are exposed for long periods - even at low levels (WHO 2022 b).

The app seeks to bring worldwide consistency to UV reporting and public health messaging. It was developed by the Cancer Council Victoria and the Australian Radiation Protection and Nuclear Safety Agency, both WHO Collaborating Centres in Australia where a similar app demonstrated improved UV protection public awareness when it was used to support a decades-long, systematic public health campaign promoting sun-smart behaviour (WHO 2022 b).