You get up in the morning, take a shower, then apply a moisturizer with sunscreen of SPF 15. Then, later, you go to the beach and apply more sunscreen of SPF 30. You are not now up to an SPF 45.
To understand this, we need to understand what SPF means. It is basically a number that makes it possible to predict how long you can stay in the sun without getting burned. An SPF of 4 is supposed to protect a “normal” person who is exposed to sun for one hour. An SPF of 8 would give you the same protection against burning, but for 2 hours, etc.
The SPF 4 will protect you for the first hour, and the SPF 8 will protect you for that same first hour, plus one more, so you still get a total protection time of 2 hours. To simplify, you will receive the benefits of the highest SPF product you use before your skin will begin burning.
The lesson here -- try to apply the appropriate sunscreen for the amount of time that you will be outside. Applying SPF 50 to take a 20 minute walk in the park isn’t doing you or your skin any favors. Besides using the correct SPF level, remember that even with sunscreen on, your skin is getting some UV exposure.
Am I the only one who did not know this?
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