The Skin Types
The natural protection of human skin (approximate safe period in the sun) depends on skin type. Human skin type is divided into 6 types, of which Type 1 has shortest natural protection period and Type 6 the longest. TYPE | Features | Reaction of the skin** | Natural protection
time of skin | I | Fair skin, fair hair, blue eyes | Always sunburn | 5~10 minutes | II | Light skin, fair hair, green eyes | Always sunburn | 10~20 minutes | III | Light skin,dark hair,browneyes | Light sunburn | 20~30 minutes | IV | Dark skin, brown hair/eyes | No sunburn | Approx. 45 minutes | V | Dark skin, black hair/eyes | No sunburn | Approx. 60 minutes | VI | Black skin, Black hair/eyes | No sunburn | Approx. 90 minutes |
** Reaction of unprotected skin to 30 minutes of sunshine in midday sun of summer.
Ultraviolet Protection Factor (UPF)
This is the way clothing is rated in the new AS/NZS4399-1996 standard for the sun protection clothing. The Australian Radiation Laboratory have proposed the following UV protection rating scheme: UPF | Mean effective UVTransmission | Protection Category | UPF 10~19 | 10%~5.1% | Moderate Protection | UPF 20~29 | 5%~3.4% | High Protection | UPF 30~49 | 3.3% ~2% | Very High Protection | UPF50+ | Less than 2% | Maximum Protection |
What this means is simply that a UPF rating on a fabric of say 20 will only allow one twentieth (ie 5%) of the UVR to pass through it. So a rating of UPF+50 would only allow one fiftieth (2%) of the UVR to pass through, and that’s as good as it gets. Environmental factors that influence UV levels - Sun height—the higher the sun in the sky, the higher the UV radiation level. Thus UV radiation varies with time of day and time of year, with maximum levels occurring when the sun is at its maximum elevation, at around midday (solar noon) during the summer months.
- Latitude—the closer the equator, the higher the UV radiation levels.
- Cloud cover— UV radiation levels are highest under cloudless skies. Even with cloud cover, UV radiation levels can be high due to the scattering of UV radiation by water molecules and fine particles in the atmosphere.
- Altitude—at higher altitudes, a thinner atmosphere filters less UV radiation. With every 1000 metres increase in altitude, UV levels increase by 10% to 12%.
- Ozone—ozone absorbs some of the UV radiation that would otherwise reach the Earth’s surface. Ozone levels vary over the year and even across the day.
- Ground reflection—UV radiation is reflected or scattered to varying extents by different surfaces, e.g. snow can reflect as much as 80% of UV radiation, dry beach sand about 15%, and sea foam about 25%.
Some little known facts: - While swimming or diving, at half a meter depth UV is still 40% as intense as at the surface
- Sand reflects 25% of UV
- Indoor workers receive 10% to 20% of outdoor worker’s yearly UV exposure
- Shade can reduce UV by 50% or more
- The Beachshadow cover is designed to reduce UV by a minimum of 97.5%
- A Beachshadow shade can reduce UV by a minimum of 50%+
- 60% of UV is received between 10am and 2pm daily
- UV increases by 4% for each 300 meter increase in altitude
- Over 90% of UV can penetrate light cloud
- Clean snow reflects up to 80% of sun-burning UV
- Seek shade
- Use known UV protective clothing
- Wear a wide brim hat and UV protective sunglasses
- Use at least factor 15 sunscreen
- If you can, check out the UV daily index for your location
Summary
You will find more links to various agencies such as the World Health Organisation and various government agencies with details in more depth on Sunsense. If you could just remember one thing, the next time you are outside taking in the warmth of the sunshine, try to use sunsense for you and your family’s well being. “Have fun in the sun but don’t get overdone” |
