What Sun Protection Factor do I need?

What Sun Protection Factor do I need?

Each skin type has its own natural protection time and without the appropriate sun protection you should not stay in the sun longer than this. Using a sun protection factor (SPF) prolongs the time you can stay in the sun without running the risk of getting sunburn. The following formula can be used as an approximation of how long it is safe to stay in the sun.

Skins own protection time x sun protection factor

For example, if you have fair skin that (without sun protection) allows you to stay outside in the sun without getting burnt for 10 minutes this means;

10 mins x SPF15 = 150 minutes (2 hours and 30 minutes)

10 mins x SPF20 = 200 minutes (3 hours and 20 minutes)

10 mins x SPF50 = 500 minutes (8 hours and 20 minutes)

This formula can be applied to all sun protection factors.

It is important to re-apply sun cream during this time however once you have reached your sun exposure limit it is advisable not to expose skin any longer even if more SPF has been applied.

Remember that for all sun protection, the SPF is a measure against the protection of UVB rays (not UVA rays). It is important to choose a broad-spectrum product which protects against UVA rays also.

It is also important for us to note here that an SPF30 does not give double the protection of an SPF15, in fact the increase in protection is only around 5%. We explain this in more detail a bit further down the page.

What is the difference between UVA and UVB rays?

Ultraviolet light, or UV light, is light from the sun that is not visible to the naked eye. There are three types of UV light, UVA, UVB and UVC. However UVC light, which is short-wavelength, is filtered by the atmosphere and does not reach the earth's surface, so we shall only focus on UVA and UVB lights here.

UVA light is long-wavelength. This means that the rays penetrate deep into the skin. These rays, which are associated with premature ageing of the skin, can cause damage to the elastin and collagen fibres which make skin supple and firm, causing a loss of tightness, can assist the development of free radicals and can cause permanent harm to DNA. While it was believed that it was UVB rays (not UVA) that can cause the development of skin cancer, the World Health Organisation (WHO) has stated that they no longer believe this to be the case;

“For a long time it was thought that UVA could not cause any lasting damage. Recent studies strongly suggest that it may also enhance the development of skin cancers.” - WHO

UVB light is medium-wavelength. These rays penetrate the top ‘superficial’ layers of skin and are the main cause of sunburn. They do significant damage to the DNA at the heart of the skin cells and significantly promote the development of skin cancer.The sun protection factor (SPF) is what protects against UVB rays.

A product with SPF15 will block about 92% of UVB radiation.

A product with SPF20 will block about 95% of UVB radiation.

A product with SPF30 will block about 97% of UVB radiation.

A product with SPF50 will block about 98% of UVB radiation.