Small amount of ultraviolet (UV) radiation are beneficial for our body, as it helps in vitamin D production. On the other hand, prolonged and excessive exposure to ultraviolet rays has harmful effects on health. Sunburn is a known short term side effect of excessive exposure to uv rays. Prolonged and excessive exposure causes pigmentation, photoaging and imposes the risk of skin cancers and cataract.
What is Ultraviolet index (UV Index)?
The UV index is an international standard scale to estimate the ultraviolet radiations at given place and time. The index informs the general public the level of UV radiation on given day, especially at midday when the sun is highest at the sky. This international scale was developed by Canadian scientists in 1992, and then adopted and standardized by the UN’s World Health Organization and World Meteorological Organization in 1994.
The UV Index for India is developed and proposed by the Ministry of Earth Sciences (MoES) after extensive research work based on the analysis of the time series of long term stratospheric ozone data and carrying forward from the guidelines of World Health Organization (WHO).
The UV Index provides the expected risk of over-exposure to the sun. It is a useful tool to help general public to take steps to reduce ultraviolet radiation exposure.
The amount of UV radiation reaching the surface is primarily related to the elevation of the sun in the sky, the amount of ozone in the stratosphere, and the amounts of cloud cover. Thick clouds greatly reduce ultraviolet radiation, but paradoxically thin clouds tend to increase ultraviolet radiations coming to surface. The peak ultraviolet radiation level changes around year. Highest radiations occur during summers and weakest during winters.
How is the grading of UV index done?
The UV index is graded on a linear scale of 1 to 10+, where 1 indicates a low risk of overexposure (at midnight) and 10+ signifies an extreme risk. Higher the UV Index, the greater the UV radiations and smaller the time it takes before skin damage occurs. It can be categorised according to risk it imposes to skin. This data is for Indian skin and can be freely accessed here.
UV Index 1-4: No risk so no need to worry.
UV Index 5: Low risk means that there is nothing to worry about as the sun will not harm you. Redness (erythema) will appear in 2 hours or more on exposure.
UV Index 6-9: Medium risk means that the sun is not dangerous, but you should avoid being in direct sunlight for more than 1 to 2 hours. Redness (erythema) will appear after longer exposure.
UV Index 10 or more: High risk means you could burn within half an hour to one hour. So try to keep out of direct sunlight.
What precautions to take when UV index is medium to high risk?
- Wear some sun-protective clothing as full sleeved and full length clothes that cover as much as skin as possible.
- Use hat, scarf or face cover to protect your face, head, neck and ears
- Use umbrella
- Use SPF30+ sunscreen – make sure it is broad spectrum and water resistant. Put it on 20 minutes before you go outdoors and every two hours afterwards. Sunscreen should never be used to extend the time you spend in the sun.
- Seek shade
- Wear sunglasses to protect your eyes.
- Avoid suntanning and tanning beds
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Dr Monika Misra
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