Sunlight affects our skin in a number of different ways. Most of the effects are caused by ultraviolet radiation. There are three types of UV radiation: UVA, which makes up most of the UV light reaching the earth’s surface; UVB which is potentially the most damaging; and UVC, most of which is filtered out by earth’s atmosphere.
UVA radiation causes tanning
UVA radiation penetrates to the lower layers of the skin, where it triggers a special type of cell called melanocytes to produce the pigment melanin. This pigment darkens the skin, resulting in a tan. The melanin provides the skin with a small degree of protection against further damage, as it helps to filter out harmful UV radiation in the future. UVA rays are used in sunbeds to create an “artificial” suntan.
UVA radiation causes premature aging
UVA rays can penetrate to the lower layers of the skin, where they may stimulate a number of changes associated with premature aging. UVA is known to cause wrinkling of the skin: this occurs either due to thinning of the skin, for example on the face, or due to its thickening, for example on the back of the neck.
UVA can also cause changes to the blood vessels supplying the skin. Sun-damaged skin is more easily bruised, and tiny vessels may appear visible near the surface of the skin: this is known as telangiectasias.
UVA may also cause an increase in the number and size of freckles. These are known as solar lentigos and are more common in fair-skinned individuals.
UVA radiation may cause skin cancer
UVA radiation was not originally thought to cause skin cancer, but recent studies suggest a link between UVA exposure and carcinoma (Wishermann et al, 2008). This development is important as tanning booths use UVA light, so this makes the safety of sun beds much more questionable.
UVB radiation causes sunburn
Sunburn is not caused by heat from the sun (infrared radiation) so it can occur even on cold days. It is caused by UVB rays, which can damage the DNA of skin cells. As the body tries to repair the damage, blood flow to the area is increased, which is why sunburned skin looks red. The damaged cells then need to be destroyed: and they are lost from the surface of the skin through peeling.
Sunburn is the body’s defence mechanism against the development of skin cancer. If damaged cells are not destroyed in this way they may begin to grow uncontrollably, resulting in a tumour.
UVB radiation causes skin cancer
UVB radiation has long been known to cause damage to DNA which may result in skin cancer. It may cause carcinoma or melanoma, the more malignant form of skin cancer. It is therefore very important to protect the skin from over-exposure to UVB radiation by using an appropriate sunscreen.
Sources:
K Wishermann, S Popp, S Moshir “UVA Radiation Causes DNA Strand Breaks, Chromosomal Aberrations and Tumorigenic Transformation in HaCaT Skin Keratinocytes” Oncogene 27, 4269-4280 (2008)
Cancer Research UK Sunsmart website
Skin Cancer Foundation "Understanding UVA and UVB"
Skinsight website
Read on:
The Ozone Layer - How it Protects Against UV Damage
Sunscreen - How Does Suncream Protect Against Sunburn and Cancer?
How Ultraviolet Rays Cause Skin Cancer - A Layman's Guide
Understanding Sunscreen Labels - Choosing the Right Suncream
Veronica Mitchell - Veronica studied veterinary medicine at Cambridge University before becoming a secondary school science teacher. She enjoys writing about ...
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