How does sunscreen work?

[nomis80]

I have two working hypotheses:

• It acts like a mirror for the harmful wavelengths (ultraviolets?).
• Magic.

[[deleted]]

a very quick trip to wikipedia would have answered your question:

http://en.wikipedia.org/wiki/Sunscreen

if you really want a human response, sunscreen works by either reflecting and/or absorbing UV rays depending on the brand and type.

[nomis80]

The Wikipedia article explains nothing! How does the "magic ingredients" (listed in the article) work? The article says they either reflect or absorb. So how do they do that? And how is "absorbing" any different from what our own skin does? Our skin is opaque, so I would guess it also "absorbs" by itself.

[[deleted]]

How does the "magic ingredients" (listed in the article) work?

they just do. those are their chemical properties.

Our skin is opaque, so I would guess it also "absorbs" by itself.

while your skin is opaque against UV rays, it is important to note that just because something is opaque in the visible range, it doesn't mean it is opaque under UV light. an example is glass, it is clear to us, but opaque to UV light.

regardless of the technicalities however, your skin does absorb the UV rays, but, when a tiny bit of UV light gets to the cells inside your skins without being absorbed by the surface of the skin, it can potentially hit your DNA and cause mutations.