SPF 30

What does 'SPF 30' 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 30, it means the sunscreen will provide 30 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 30, you will take 300 minutes before you burn.

Put another way, a sunscreen with an SPF of 30 will delay the onset of a sunburn in an individual who would otherwise burn in 10 minutes to burn in 300 minutes. Alternatively, the SPF 30 sunscreen allows a person to stay out in the sun 30 times longer than when unprotected from the sun's UVB rays before getting sun burnt.

A common question asked is whether or not SPF 30 has twice as much sun protection as SPF 15. UVB protection does not actually increase proportionately with a designated SPF number. For example, an SPF of 30 screens 97 percent of UVB rays, whereas an SPF of 15 screens 93 percent of UVB rays, and an SPF of 2 screens 50 percent of UVB rays. However, this is the theory, but in actual fact there are other aspects to consider. There are many influences on the effectiveness of the SPF that may result in a lower SPF than the product contains. Some of these include:

Most people feel safer using an SPF 30 rather than an SPF 15 because of the extra protection but it's up to you to decide which SPF rating will suit your skin's needs in your specific circumstances. If you know that your skin burns easily or that it doesn't take very long for it to get sunburned, SPF 30 is definitely recommended over SPF 15.

See this World Health Organization page for a public guide on UV levels and their intensities. You can find daily reports of UV light levels, which can also help you determine how much protection you should opt for.

Another recommendation is to make sure you choose a product that is labeled as a broad spectrum sunscreen that will effectively fight against both UVA and UVB rays. There is currently no uniform measure of UVA absorption, although there are a few options available and you are recommended to look for a sunscreen that has been certified by at least one of them. EG. the Boots Star system.

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:

However, specifically developed and manufactured sun-protective clothing is usually SPF 30 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. Using a higher SPF provides greater UVB protection than a lower SPF, but it does not mean that you should stay out in the sun longer, regardless.

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