The SPF stands for Sun Protection Factor. It is a measure of the protection against UVB or ultraviolet B light only. If you develop a sunburn after 20 mins in the sun, using an SPF 10 sunscreen will protect you up to 200 mins before you develop a burn.
In practice, the amount of sunscreen applied is much less that the amount used during laboratory testing so the actual protection from using the sunscreen is less. Generally, we recommend an SPF of at least 30.
Besides UVB protection, do read the sunscreen labels to look for the protection against UVA too. It is important for the sunscreen to have both good UVA and UVB protection as UVA can also damage the skin.
