This section gives information about UV (ultraviolet) radiation, and how it can affect our health.
Why is UV exposure important to health?
Our main exposure to UV radiation is through sunlight. UV exposure can affect our health in a number of ways. Too much UV exposure can cause melanoma, non-melanoma skin cancer, and cataracts. Too little UV exposure can lead to vitamin D deficiency, which can affect bone health and immune system function.
New Zealand has relatively high UV levels, and one of the highest melanoma rates in the world.
What is UV radiation?
UV radiation is part of a broad spectrum of wavelengths from the sun. UV radiation has a shorter wavelength than visible light, and we can’t feel or see it.
Most UV radiation is absorbed by the ozone layer. However, some UV radiation still passes through to reach Earth’s surface.
UV radiation is classified into three types, according to the wavelength: UVA, UVB and UVC. However, UVC radiation is entirely filtered out by the atmosphere, leaving UVA and UVB as the primary causes of health conditions associated with exposure to UV radiation.
Health effects of excess UV exposure
Too much UV exposure can cause health problems, of which melanoma and non-melanoma skin cancer are among the most serious. New Zealand has some of the highest rates of melanoma incidence and mortality in the world.
The main health effects from excess UV exposure include:
UV exposure causes about 90 percent of skin cancer cases. A person’s UV exposure and risk of developing skin cancer depends on:
- genetics – including skin pigmentation (people with fairer skin are more at risk)
- behaviours – using sun protection, the type of clothes worn, sun tanning, use of sun beds
- immune competence – for example, having HIV increases the risk of developing skin cancer.
Read the latest statistics on melanoma on the melanoma webpage.
Too little UV exposure can lead to vitamin D deficiency
We need a small amount of UV exposure to produce vitamin D. Vitamin D is important for good bone health, and sunlight is our main source. Low vitamin D levels can cause:
- rickets (resulting in bowed legs and knocked knees) in children
- osteoporosis and osteomalacia (affecting the bones) in adults.
Read the latest statistics on vitamin D deficiency on the vitamin D deficiency webpage.
New Zealand’s UV levels
In New Zealand, UV levels are higher:
- during summer: UV levels are highest during summer, and are also fairly high during autumn and spring
- in the north: UV levels are higher closer to the equator
- on sunny days: as clouds can reduce the amount of UV reaching the Earth's surface
- during the middle of the day: UV levels are typically highest from 11am to 3pm.
In New Zealand, peak UV levels are about 40 percent higher than in similar latitudes in North America . This is because:
- The Earth is closer to the sun in December and January
The Earth has an elliptical orbit, and passes closest to the Sun during December and January. This means that the sun is closer to New Zealand in our summertime than it is to northern hemisphere countries in their summertime.
- Low air pollution levels lead to higher UV levels
New Zealand has a comparatively ‘clean’ atmosphere due to its remoteness and low population density. This means that UV radiation can pass through the atmosphere relatively unhindered.
- Ozone hole lets through more UV radiation
In summer, ozone-depleted air moves over New Zealand from Antarctica. This ozone hole means there are less ozone molecules to absorb UV radiation before it reaches Earth’s surface.
Read more about UV levels in New Zealand on the daily UV levels webpage.
The UV Index
The standard way to report UV levels is the Ultraviolet Radiation Index (UVI). The UVI is an international, scientific measure of the level of UV radiation from the sun.
The higher the number on the UVI index, the higher the radiation level. A UV Index of 3 or more requires protection from the sun. At this level, UV levels are enough to damage the skin, and increase the risk of skin cancer.
Table 1: UV index levels and sun protection precautions
Source: McKenzie 2008 
Reducing your risk of skin cancer
Be sunsmart – protect yourself when the UV Index is 3 or above. You can protect yourself by:
- using sunscreen
- wearing a hat
- wearing sunglasses
- wearing sun-protective clothing
- staying in the shade
- staying indoors during the middle of the day.
Visit the SunSmart website
Get some sunshine each day during winter. This is particularly important during winter for people living in the South Island, to help prevent vitamin D deficiency.
Get checked for skin cancer at your health professional.
1. McKenzie R, Bodeker G, Scott G, Slusser J, Lantz L. 2006. Geographical differences in erythemally-weighted UV measured at mid-latitude USDA sites. Photochemical and Photobiological Sciences 5(3): 2223-2226. doi: 10.1039/B510943D
2. McKenzie R. 2008. A Climatology of UVI for New Zealand. Wellington: NIWA.