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If I used a good spf on my face say 15 or above before going on a sun bed, would this filter the harmful rays? If so would the rays kill bacteria that causes acne or would this be filterd aswell by the spf?

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If I used a good spf on my face say 15 or above before going on a sun bed, would this filter the harmful rays? If so would the rays kill bacteria that causes acne or would this be filterd aswell by the spf?

No it wouldn't filter the harmful rays at all.

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The key is what you mean by "harmful." Yes, most sunscreen do a good job of filtering out the burning UVB rays that cause sunburn and are the worst contributors to skin cancer. An SPF-15 sunscreen cuts the UVB by 15x.

The problem is that UVA also causes damage. It is clear that UVA can cause premature aging, and it *may* contribute somewhat to skin cancer. Most sunscreen do not filter UVA very well (and some not at all). A few of the newer ones do, but my understanding is that even the ones that filter UVA, don't do it as well as they filter UVB.

Lastly, there is the question as to whether tanning beds emit the necessary wavelengths to kill the P.Acnes bacteria. The beds probably do not have as much light in the 420nm range as the special lamps do (no particular reason for the fluorescent UV tube manufacturers to waste some of the energy in a wavelenth that doesn't provide tanning). While they have lots of light at the shorter wavelengths that can also kill P.Acnes, those wavelengths are in the UVA and UVB ranges where you are trying to minimize exposure by applying the sunscreen.

Thus my quick off-the-cuff guess is that a sunbed won't kill a lot of the P.Acnes bacteria with sunscreen on and is a bad idea without it. The special violet/blue 420nm lamps kill the bacteria using a wavelength that is not harmful and not filtered by sunscreen.

Note, though, that real natural sunlight DOES have a fair amount of 420nm light (but still less than the professional-strength 420nm lights in the doctor's office). Thus natural sunlight with sunscreen applied should work at least some.

(420nm being at the violet end of the spectrum just above the UV range)

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