Ultraviolet radiation
Ultraviolet (UV) radiation covers the wavelength range of 100–400 nm, which is a higher frequency and lower wavelength than visible light. UV radiation comes naturally from the sun, but it can also be created by artificial sources used in industry, commerce and recreation.
The UV region covers the wavelength range 100-400 nm and is divided into three bands:
- UVA (315-400 nm)
- UVB (280-315 nm)
- UVC (100-280 nm).
As sunlight passes through the atmosphere, all UVC and approximately 90% of UVB radiation is absorbed by ozone, water vapour, oxygen and carbon dioxide. UVA radiation is less affected by the atmosphere. Therefore, the UV radiation reaching the Earth’s surface is largely composed of UVA with a small UVB component.
The amount of UV radiation from the sun that hits the Earth’s surface depends on several factors, including the sun’s height in the sky, latitude, cloud cover, altitude, the thickness of the ozone layer and ground reflection. Reductions in the ozone layer due to human-created pollution increase the amount of UVA and UVB that reaches the surface. This can impact human health, animals, marine organisms and plant life. In humans, increased UV exposure can cause skin cancers, cataracts and immune system damage.
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.
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.
Children’s UV exposure should be carefully limited because they are in a dynamic state of growth and therefore more susceptible to environmental threats than adults. Many vital functions such as the immune system are not fully developed at birth, and unsafe environments may interfere with their normal development.
WHO works with Member States and partners to increase public understanding of the effects of overexposure to ultraviolet radiation.
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, to encourage countries to take action to reduce UV-induced health risks and to provide guidance to national authorities about sun awareness programmes.
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.
