The sun sends out different types of radiationthat reach the earth – visible light that is seen as sunlight, infrared radiation felt as heat andultraviolet radiation (UVR) that we can’t see. Ultraviolet radiation can be classified as UVA, UVB, or UVC.
The ozone layer absorbs some, but not all, of these types of UV radiation:
UVA:
Wavelength: 320-400 nm. Not absorbed by the ozone layer.
UVB:
Wavelength: 290-320 nm. Mostly absorbed by the ozone layer, but some does reach the Earth’s surface.
UVC:
Wavelength: 100-290 nm. Completely absorbed by the ozone layer and atmosphere.
UVA rays account for up to 95% of the UV radiation reaching the earth’s surface, and can penetrate clouds and glass. These UVA rays play a major part in photo-damage and skin ageing. UVB rays are the chief cause of skin reddening and sunburn, damage which can also lead to premature skin ageing. Both UVA and UVB rays have the potential to cause skin cancers.
Effects of UV Radiation on the skin
Photoageing is the premature ageing of the skin due to repeated excessive exposure to ultraviolet radiation (UV rays). It is extremely prevalent in Australia, due to the harsh climate and an outdoor lifestyle.
Photoageing can be characterised by the following visible signs of skin ageing:
• Fine lines & wrinkles
• Hyper-pigmentation
• Uneven skin tone or skin dullness, coarse skin texture
• Loss of skin firmness or elasticity
• Facial redness
Skin cancer is a disease of the body’s skin cells. It forms when skin cells are damaged by UV radiation penetrating the skin. UV damages skin cells’ DNA and this can cause cells to mutate and grow abnormally. If these mutant cells are not destroyed through the body’s own processes or other means, they will continue to develop and can turn into skin cancers.
Sunscreens Explained
After understanding the skin risks associated with UV exposure the importance of sun protection becomes apparent. There are a few different measures that indicate the efficacy of a sunscreen and that are recognised in Australia and regulated by the Therapeutic Goods Administration (TGA).
Sun Protection Factor (SPF) is a measure of a sunscreen’s ability to prevent UV radiation from damaging the skin. SPF measures the amount of UVB radiation transmitted to the skin after sunscreen has been applied compared to the amount of UVB transmitted to the skin without sunscreen. A sunscreen with an SPF of 30 provides 30 times more protection than if not wearing a sunscreen. A sunscreen with an SPF of 50 provides 50 times more protection than if not wearing a sunscreen.
Broad Spectrum is a measurement of a sunscreen’s effectiveness against UVA rays. Broad Spectrum sunscreens are designed to protect against both UVB and UVA rays. A conventional sunscreen that has an SPF rating only and does not mention the term “Broad Spectrum” may block very little UVA radiation relative to the nominal SPF.
