How does sun tanning work?


A sun tan occurs when your skin acts to protect you from harmful ultraviolet rays. Sunlight comes in different forms: infrared (heat), visible light and ultraviolet (UV).  There are two types of UV rays involved in tanning: UVA and UVB.  UVA radiation, also known as black light, is what makes us tan. It can’t penetrate the skin as deeply as UVB rays as it has a longer wavelength, which is why UVB rays can cause sunburn and UVA is responsible for tanning.

What happens to your skin when it tans? The amount of pigment in the skin, and how quickly the body can make it, determines the skin’s ability to tolerate sun exposure.  When the outer layer of skin, called the epidermis, is exposed to UV it stimulates specialized cells called melanocytes to produce a pigment called melanin. The melanin absorbs the UV radiation.  In doing so, it protects our skin cells from UV damage.  The melanin is contained in tiny granules that spread out across the top layer of skin that has been exposed to UV and give you a tan color.

Why does it take a few days for sun tan to develop? Melanocyte cells need to be exposed to UVA rays for a short time before they can create melanin.  It then takes a few hours for the pigment to be made. After 5-7 days relaxing on the sun lounger, our skin will start to darken as the cells move closer to the skin's surface and continue to produce more melanin.

It’s important to stay safe when out in the sun as too much exposure can cause sun burn, premature ageing and skin cancer.  Avoid sunbeds, these can cause long-term serious damage to the skin.  Make sure you choose the right sun cream for your skin type.  Broad spectrum sun screams with high SPF (sun protection factor) like 30 are recommended. Try to wear a wide brimmed hat, loose-fitting clothes and sunglasses to protect eyes from UV rays. Sit in the shade as much as possible.  Everyone has a cut-off point to how much melatonin they can produce, this is usually about 2 to 3 hours or less for pale skinned people, so there’s no point sunbathing for the whole day. Eat foods rich in lycopene like tomatoes to boost sun protection.

Some people have continuous melanin due to their ethnic background. This means their skin always has varying degrees of pigment, depending what part of the world they are from. The higher the melanin the lower the skin cancer rates.  Those with red hair tend to not tan easily. This is due to the balance of two pigments: eumelanin (brown) and phaeomelanin (yellow and red) which are produced by Melanocyte cells.  Some have absolutely no melanin in their hair or skin, these are called Albinos. This is due to a lack of tyrosinase, an important enzyme used in the production of melatonin.

Weather conditions, time of year, time of day, altitude and geographic location all determine how we tan. Some surfaces can amplify UV exposure by causing it to reflect. For instance, snow reflects 90% of UV light which is why you can get a tan whilst snow-boarding on a sunny day. 

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