Sun and skin – a dangerous combination
Box 6 | Sunblocks and sunscreens
When there is no way of avoiding the sun – through shade or suitable clothing – the final resort is to apply protection to the skin.
Sunblocks physically prevent sunlight from reaching the skin, mainly by reflecting it. They are usually a cream containing a metal such as zinc oxide or titanium dioxide. They are rarely used for whole body protection, being kept for regions of high exposure such as the nose.
Sunscreens are chemicals that absorb ultraviolet (UV) radiation. Most contain compounds called para amino benzoic acid (PABA) or benzophenone and its derivatives. Others may also contain esthers of cinnamate. Sunscreens are sold with a sun protection factor (SPF) number. The higher this number, the greater the power to block ultraviolet radiation. In theory, a person can spend longer in the sun with a sunscreen of a higher SPF rating.
There’s no doubt that, if properly and regularly applied, sunscreens prevent sunburn. But ultraviolet radiation does more than just burn the skin. Some controversy exists over whether sunscreens, as opposed to sunblocks, provide adequate protection against the effects of ultraviolet radiation on the immune system in the skin. (Most sunscreens absorb more UV-B than UV-A.) And the ultimate question of how effective they may be in stopping the long-term development of cancer has also been raised.
There are differences of opinion here. Some believe that sunscreens provide a false sense of security by encouraging people to spend longer in the sun. Without any burning it is easy to remain outside far longer than we normally would. But others say that it is better to be protected than to suffer sunburn.
Another line of argument about sunscreens relates to the chemistry of their constituents. Just how safe are the compounds in sunscreens – especially when exposed to light and ultraviolet radiation, both of which can cause chemical changes? In addition, a proportion of the active compound is absorbed by the skin. What effects might it have?
Some people are worried about nanoparticles of zinc oxide that are present in some sunscreens (nanoparticles are particles smaller than 100 nanometres; one nanometre is one-billionth of a metre). Particles this small do not reflect sunlight, so the sunscreen appears clear when rubbed into the skin. However, there is some concern that these tiny particles can penetrate the skin, and subsequently cause damage to cells and DNA. Recent studies have confirmed that zinc from sunscreen can enter the bloodstream, but the concentrations were very low, easily within the limit that the body can cope with. Furthermore, it was impossible to tell if the zinc was still in the form of potentially dangerous nanoparticles or simply dissolved zinc ions. The general scientific consensus is that the dangers of not wearing sunscreen outweigh potential risks posed by the nanoparticles in some sunscreens.
The body’s own sunscreen, melanin, is undoubtedly effective when present in large enough amounts, as is attested by the fact that dark skinned people have a rate of skin cancer at least 10 times lower than white people. White people in countries like Australia will always need additional protection because their skin simply cannot manufacture enough melanin.
The medical establishment still strongly supports the use of sunscreens and there is no doubt that if you have to remain in the strong sun you are better off with one than without one. A sunblock is probably better still. Under consideration is whether the total effectiveness of sunscreens can be improved and whether any risks can be minimised.
Boxes
Box 1. The ultraviolet family
Box 2. Types of skin cancer
Box 3. The molecular mechanisms of skin cancer
Box 4. Diagnosing skin cancer
Box 5. Australian research
Related sites
Sunscreens and photoprotection (e-Medicine.com)
Sunscreens (The Electronic Textbook of Dermatology, The Internet Dermatology Society, USA)
Position statement – use of SPF30+ sunscreens (The Cancer Council, Australia)
Warning: contains nanotech (Cosmos, 12 September 2011)
Nanoparticles in sunscreens raise questions of safety (Cosmos, 3 March 2010)
Sunscreen and nanoparticles (Choice, 30 September 2010)
Nanoparticles and sunscreen (The Cancer Council, Australia)
Page updated December 2011.