What does 'SPF 25' mean? SPF stands for 'Sun Protection Factor' and the number is determined experimentally indoors by a certified laboratory through exposing various human subjects to a light spectrum that is designed to imitate the sun's UVB rays at noon. Starting with a base understanding of how long it would take the individual's skin to burn, they calculate how long it takes to induce redness in sunscreen-protected skin. If the resultant SPF is 25, it means the sunscreen will provide 25 times more protection than if the individual had worn no sunscreen. Eg if you take 10 minutes to turn red, wearing a sunscreen classified SPF 15, it will take 150 minutes before you burn.

Put another way, a sunscreen with an SPF of 25 will delay the onset of a sunburn in an individual who would otherwise burn in 10 minutes to burn in 250 minutes. Alternatively, the SPF 25 sunscreen allows a person to stay out in the sun 25 times longer than when unprotected from the sun's UVB rays before getting sun burnt.

Make sure you choose a product that is labeled as a broad spectrum sunscreen that will effectively fight against both UVA and UVB rays.

Sun protective clothing is also available with official SPF levels having been measured. They are however, measured for both their UVA and UVB protective levels. Without any specific testing, the following provides a view on the SPF's various types of clothing would provide:

•Nylon Stockings or socks - SPF 2
•Hats - SPF 3-6
•Summer-weight clothing or T-shirts - SPF 6-8

However, specifically developed and manufactured sun-protective clothing is usually SPF 15 but can measure up to SPF 45.

Whichever SPF you choose, wearing sunscreen should not provide a false sense of security about protection from UVB exposure. No sunscreen can provide 100 percent UVB protection.

After all, it's really the burning that you want to omit, as that is what causes skin damage and potentially skin cancer.