Sunscreen, Cumulative SPF protection, sunburns, and Skin Cancer

mrschili asks:

Let’s say that I get up in the morning, take a shower, then apply a moisturizer with sunscreen – spf 15, say. Then, later, I go to the beach and, because I am the whitest white person I know and am averse to pain, I apply more sunscreen – say I bought me some spf 30 this time. Am I now up to spf 45? Is sunscreen cumulative?

To understand this, you first have 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 problem here is, what is “normal” and what is “sun”? These two variables makes it pretty hard to predict exactly what to expect when you slather on sunscreen. Keep in mind that sunscreen doesn’t claim it will prevent you from getting a sunburn – it will just take longer.

Of course, your real question is do “stacked” applications of sunscreen combine to create a “super” sunscreen, and the answer is (unfortunately), no. If you put on a layer of SPF 4, and follow it with a layer of SPF 8, you do not have a combined SPF or 12. The SPF 4 will protect you for the first hour, and the PSF 8 will protect you for that same first hour, plus one more, so you still get a total protection time of 2 hours. Note that waiting the 2 hours and then adding another layer won’t make any difference – you’ve already used up your 2 hours.

The key to remember is that the sunscreen is acting like a filter. If your skin can handle X units of UV exposure before it begins burning, and you apply SPF 4 sunscreen, after 1 hour, your skin is ready to start burning – you’ve used up all of your safe exposure. Even if you apply SPF 10,000, the UV that gets through will begin to burn your skin immediately. The trick to using sunscreen (if you actually use sunscreen) is to apply the appropriate SPF for the amount of time you expect to be in the sun.

Remember: Sunscreen is not meant to replace common sense. Your skin knows what to do with sun exposure. It is incredibly adaptable, and can react to protect itself from reasonable exposure to sun. The problem is when someone spends a long time inside, then suddenly decides to go outside. They have taken their skin from a dark place to a bright place without giving it a chance to adjust. Think about what happens to your eyes when you walk out of a dark movie theater into bright sunlight. Your skin does the same thing, but it takes a lot longer – while it is adjusting to the sudden increase in sun exposure, you get sunburned. Instead of relying on sunscreen, a much more rational approach is to slowly build up your tolerance to sun exposure. Start out with a short stay (you will know what a short stay is – for some it will be a few minutes, for others an hour or so) in the sun, then cover up. Slowly increase the amount of time that you spend in the sun. Not only will your skin adapt, but you will develop a wonderful tan (that’s just your skin adapting to being exposed to the sun).

That isn’t to say that turning into a sun worshipper is a good thing. Sunburns cause real damage to the skin, and repeated burns can contribute to your chances of getting skin cancer. If you must suddenly change your sun exposure, sunscreen is definitely the way to go. It will help protect your skin while you slowly adapt to being in the sun. The trick here is to remember that you are providing a crutch to your skin when you use sunscreen. Just like Heroin, your skin can get hooked on the sunscreen. It will get lazy, and stop trying to protect itself from the sun. Chronic sunscreen users actually get hooked on sunscreen – without the stimulation provided by sun exposure, your skin produces less and less of the stuff it needs to protect itself. So, when you do find yourself in a situation where you need to wear sunscreen, use your smarts: Use the appropriate level of SPF sunscreen – applying SPF50 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. That means that it (if you are using the right sunscreen) will be building up a tolerance for sun exposure. As your tolerance increases, you will need to decrease the SPF you are using. Remember, sunscreen is like methadone for a heroin junkie – you should be using it to wean yourself away from needing the fix (or in the case of sunscreen, the protection).

The exception to the “wean off it” rule is the person that (for whatever reason) is stuck inside – be it in an office, at home, ro whatever – for the majority of the time, and wants to spend their days off outside. If you are only outside occasionally, or erratically, sunscreen will provide the protection that your skin will need. While this is less than ideal, it sure beats a series of bad sunburns….

One Response to “Sunscreen, Cumulative SPF protection, sunburns, and Skin Cancer”

  1. mrschili Says:

    I guess I knew about what SPF was all about, I just didn’t know if we could “layer” protection. Thanks for this!

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