Wednesday July 21 2010
An umbrella on its own does not offer total protection
“Beach shades will not keep off the sun's deadly rays,” the Daily Mail warned. The newspaper said that a third of cancer-causing UV rays still reach the skin even when people are in the shade.
This experimental research conducted in Spain involved placing a UV sensor beneath a large beach umbrella. Although the umbrella absorbed most of the direct UV radiation from the sun (only 4% passed through), about 34% of the ‘diffuse’ radiation (reflected off surfaces or scattered by air molecules) from around the umbrella reached the area beneath it.
It should be pointed out that the research relied on complex mathematical formulae, and the findings may be restricted to the environmental circumstances, and the dimensions and material of the umbrella used. In addition, no humans were actually involved in the experiments, so direct damage to the skin was not demonstrated.
However, the researchers’ conclusions seem appropriate: that an umbrella on its own does not offer total protection from the sun. As such, it should be considered as an additional physical barrier, and appropriate sunscreens with an adequate SPF should also be used.
Where did the story come from?
The study was carried out by researchers from Universidad de Valencia in Spain and the University of Tasmania in Australia. Funding was provided by the Ministerio de Ciencia e Innovaciòn, Spain. The study was published in the peer-reviewed scientific journal Photochemistry and Photobiology.
The Daily Mail has clearly and accurately reported this research.
What kind of research was this?
This experimental research was set up to develop a mathematical model that could estimate a person’s level of exposure to ultraviolet light (UV) when they are under partial cover (for example, an umbrella). The researchers tested their model by investigating how much UV penetrated a beach umbrella. They measured both direct UV rays from the sun and diffuse UV, which is reflected off surfaces or scattered by air molecules.
Excessive UV exposure is known to have several detrimental effects on human health, damaging the skin and eyes, and increasing the risk of skin cancers and cataracts. The main methods of UV protection are physical barriers (including manmade barriers such as beach umbrellas, and natural barriers such as the atmosphere or trees), and chemical and biological agents (creams, sprays and lotions).
What did the research involve?
The experiments were conducted throughout the midday hours, when the sun was at its peak, in December, under cloudless skies in Spain. For the physical test of their model, the researchers used a white and blue coloured beach umbrella that was about five feet wide (80cm radius) and five feet high (150cm).
The researchers called their new mathematical model the ‘sky view factor model’. The calculations are complex but, essentially, the model mimics the amount of UV a human body might receive when stretched out underneath the centre of a beach umbrella.
The model was tested using the white and blue umbrella. The amount of diffuse radiation that penetrated the shade of the umbrella was measured using a device called a ‘shadowband’, which blocked all direct sunlight and only measured the UV from other sources. A light sensor positioned under the middle of the umbrella also measured how much UV could pass directly through the umbrella. They measured the level of ‘erythemal UV radiation’, the spectrum of UV radiation that will cause redness to the skin.
Their experiments took into account the elevation of the test site and the transmission of radiation reflected from the ground.
What were the basic results?
The researchers say that their mathematical model agreed with the measurements conducted with and without the beach umbrella. They also say that the umbrella absorbed most of the direct radiation, letting only 5% of it through.
However, the sensors at the bottom of the umbrella detected that 34% of the diffuse radiation from the umbrella’s surroundings penetrated the area under the umbrella.
How did the researchers interpret the results?
The researchers say that the beach umbrella effectively blocked direct radiation from the sun. However, diffuse radiation from the surroundings, which accounts for about 60% of the UV involved in causing damage to the skin, still reached the sensor under the umbrella.
This model may help to determine the UV exposure to humans in complex environments, and also how the physical characteristics of the environment contribute to these loads.
The researchers conducting this study formulated a complex mathematical model aimed at seeing how much UV light penetrates a typical beach umbrella. Though the umbrella was found to absorb most of the direct UV light that hit it, some radiation penetrated the area under the sunshade from the surroundings.
Points to note:
- The experiments rely on assumptions and mathematical formulae that may have some degree of error.
- These findings give some indication of how much UV radiation may be able to penetrate a physical barrier, but this experiment only tested a particular beach umbrella, and the accuracy of the model may vary when applied to other physical obstructions. The colour of the material, size of the protective shade and position of the person beneath the shade may all have an effect. The findings may also not be applicable to all materials, some of which may be specially designed to have a higher level of UV protection (for example, certain swimsuits and sun-suits for babies and children).
- There are many complexities in the environment, including cloud cover, pollution and the surface the umbrella’s erected on. The findings from this study may only apply to quite specific settings.
- These findings give no indication of how much actual UV damage to the skin would be caused in different scenarios, for example if a person also used sunscreen, as the experiment was not tested directly in humans.
The conclusions made by the researchers seem appropriate: that an umbrella on its own does not offer total sun protection. As such, an umbrella should be considered as an additional physical barrier, and appropriate sunscreens should still be used. These findings are of particular importance for babies and young children, who are often sheltered under an umbrella on a pushchair or pram, during which time they should be doubly protected by a suitable sunscreen lotion.