Ultraviolet rays / Ultraviolet radiation. Why do we need to protect ourselves against it?
We often get asked to put on sunscreen before going out in the sun. Why is it so important?
What are ultraviolet rays?
Our bodies are exposed to many forms of radiation on the electromagnetic spectrum on a daily basis. These can be radio waves, microwaves, visible light, X-rays, Gamma radiation, infra-red and ultraviolet (UV) rays.
UV falls in the portion of the electromagnetic spectrum between X-rays and visible light: The shorter the wavelength, the higher the energy; ie. UV has higher energy than visible light.
Conversely, when it comes to penetration, the longer the wavelength, the deeper the penetration.
The most common UV radiation is sunlight, which produces mainly 3 types of UV, namely:
UV-A has the longest wavelength of the three types of UV radiation we get from the sun. It penetrates deep into the deeper layer of our skin (the dermis).
UV-B has a wavelength between UV-A and UV-C. Some of this is absorbed by the Earth’s ozone layer as it passes through the atmosphere. As it has a short wavelength, it reaches only the outer layer of our skin (the epidermis).
UV-C has the shortest wavelength, all of this is absorbed by the Earth’s ozone layer as it passes through the atmosphere.
We also get UV from other sources like tanning booths, mercury vapour lighting, halogen, fluorescent and incandescent lights and some types of lasers.
What harm can UV do?
UV exposure has its benefits. UV-B specifically helps the body produce vitamin D and have also been used in the medical setting to treat certain skin conditions.
However, excessive exposure to UV radiation can result in chronic harmful effects. These include photokeratitis (inflammation of the surface of the eye due to UV exposure), photoaging/ accelerating ageing of the skin, micro-DNA damage and mutations that increase the risk of and cause skin cancers, sunburn.
Does my exposure to UV change depending on where I am or what I am doing?
Many factors determine how much UV exposure you get. These include:
Geography and Altitude
The equator receives the strongest UV rays as the sun is directly over the equator and UV travels a shorter distance of atmosphere to reach our skin. The ozone layer in the equator is also naturally thinner so less UV is absorbed compared to higher up in the northern and southern hemispheres.
Having said that, there are certain terrains that can increase UV exposure due to their reflective properties, such as snow, sand, pavement and water.
Higher land also receives more UV than lower land because there is less atmosphere.
Timing (Time of the year/ day)
The sun’s angle in relation to Earth varies with the season. During the equinoxes, the sun rests directly above the equator, whilst the solstice is when the Sun reaches its most northerly or southerly excursion relative to the equator. Hence why the northern and southern hemispheres receive more UV during their respective summer months and conversely receive less in their winter months.
This serves as a reminder that UV rays are present even on a cloudy day and it can still cause long term damage to skin and eyes. Hence, it is important to continue protecting yourself with sunscreen even if it is a cloudy day.
The UV index (UVI) is a rating scale used throughout the world to indicate the amount of skin damaging UV reaching the Earth’s surface.
In Singapore, the National Environment Agency reports the UVI. It is measured at the Changi Meteorological Station and is reported hourly from 7am to 7pm.
Protective measures should be taken if out in the sun, especially during the peak hours of 11am to 3pm.
What can I do to protect against UV?
- UV protective umbrella and seek shade
- Sunglasses that block UV-A and UV-B rays
- Wear a broad-brimmed hat
*DisclaimerInformation provided in this article is for reference and educational purposes only. It does not replace actual medical advice and consultation with your doctor.
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