The sun protection factor (SPF) indicated in your sunscreen, sun block or sun cream specify a measurement used in the laboratory to evaluate its effectiveness. The rule of thumb is, the higher the SPF the more protection for you.
So when you buy a sun protection look closely at the numbers. However, there is still another factor that you have to consider; that is the type of skin that you have. If you have a fair skin you have more chances of getting sunburn before the person who has a darker skin shade.
This is because they have a higher concentration of the dark pigment that gives color to the skin called melanin. You may also consider the activity you will have for the day, if you intend to stay outdoors apply a higher SPF. You must remember also that only 20 minutes of direct sun exposure is allowed, after which you need to let your skin cool off by looking for a shaded area.
You may also use a simple computation in determining the number of hour’s protection you have from the sunscreen you are using. Here’s the formula:
SPF X 10 = the number of minutes protection
Example: If you’re using SPF 30 (30 X 10) you get 300 minutes or 5 hours protection