A suntan is the holiday goal for many travellers. However, prolonged and unprotected exposure to the sun can cause skin damage. A suntan is the visible effect of that damage which can lead to skin ageing and melanoma.
Ultraviolet (UV) radiation is a small component of sunlight and consists of non-visible wavelengths. These UV wavelengths are subdivided into three types: UVA, UVB and UVC.
Exposure to UVA radiation is the most important cause of skin ageing, and also a cause of photosensitivity.
UVB is mainly responsible for sunburn and melanoma, and causes skin ageing.
Factors affecting UV radiation levels
Time of day
The highest levels of UV light are received when the sun is at its highest point in the sky and has the shortest distance to travel before reaching the earth’s surface. This usually occurs between local noon and 2pm, and for the two hours either side of this, i.e. 10am to 4pm, when sun exposure should be kept to a minimum.
UVA and UVB levels vary greatly between winter and summer in temperate regions but are more constant between seasons in areas closer to the equator.
Cloud cover and wind
Clouds have less effect on UV radiation levels than they do on temperature because their water content absorbs heat more efficiently than UV radiation. It is therefore possible to experience the damaging effects of the sun on cool cloudy days.
A cool wind also has a falsely reassuring effect because UVB levels remain unchanged on windy days.
White surfaces such as snow or sand reflect UV radiation resulting in more of it reaching the skin and therefore an increased risk of sunburn. Rippling water and rough seas also reflect more UVB radiation than calm open water.
Effects of UV radiation
UVA radiation stimulates production of melanin pigment in cells of the upper layers of skin, causing it to tan.
UVB radiation leads to a darker and longer-lasting tan. It also stimulates skin cells to produce a thicker epidermis in order to defend the skin against further UV damage. Skin tanning is therefore a sign that the skin has been damaged.
When UVB penetrates the deeper skin layers, it is absorbed by DNA and damage to the cell occurs. As a result the cell attempts to repair itself by releasing chemicals. Sunburn is a visible reaction to this repair process. In some cases the damage to the cell is so severe that it dies resulting in skin peeling and blistering.
Oral fluids, analgesia and non-steroidal anti-inflammatory medication can be useful in relieving these symptoms.
Topical sunscreens are one of the most common methods used to protect skin against the damaging effects of the sun. They contain chemicals that absorb various wavelengths of UV light. Sunscreens are rated by their sun protection factor (SPF). The SPF refers to the relative protection against sunburn that one receives after applying the sunscreen compared to not using it. Sunscreens with higher SPF ratings give higher levels of protection. As an example, if it takes 10 minutes for a person to become sunburned, applying a sun cream with an SPF of 15 means that it will take 15 times as long, or 150 minutes, to develop sunburn.
Changes to an existing mole, such as increasing size, itchiness or bleeding or oozing, or a new mole that develops very quickly, are potential signs of melanoma. Any such moles should be examined by a doctor.
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