Kathy,
Yes, the skin is there as a buffer zone for absorption and in ideal conditions, this works well. However, through many of the things we are exposed to in our daily lives, our absorption rate is increased dramatically, making the skins resistance to chemicals much more lax. On top of that some sunscreens have switched to a nano particle formula, which means that even more chemicals can be absorbed through your skin.
I would suggest going to www.cosmeticsdatabase.org (brought to you by the Environmental Working Group). From there you can look up the brand you have to see it's toxicity rating and what it's ingredients actually do to you, or you could search for a less hazardous brand according to what you are looking for in a sunscreen.
I personally have run all of the store bought products I use through the database. Wow, I had been buying some pretty toxic stuff. It's also really useful to look up individual ingredients for anything homemade that I'm working on so that I know the effects of what I'm creating.
Good Luck!

60% of whatever you put on your skin gets absorbed, and eventually ends up in your bloodstream. If I were you, I'd be VERY careful with sunblocks. Many of the newer ones, although they do indeed block the sun's rays, have nanoparticles in them, making absorption much more likely. This type of skin technology is very new, so they really don't know what the long-term effects of using such high-tech products are. I'd be on the safe side, and eschew the use of sun creams altogether, and concentrate instead on detoxifying the body - since the sun pulls body toxins to the skin's surface, resulting in skin cancers. Use the old-fashioned ways of protecting your skin - wear a broad-brimmed hat, long sleeves, stay in the shade, and stay inside during the middle of the day. Limit outdoor activity to either early or late in the day, when the sun's rays are less intense. Work on creating your own protection from consuming large amounts of raw produce, especially dark greens, and incorporate some sort of algae like spirulina or blue-green algae into your diet for enhanced anti-oxidant and detoxifying protection from the inside. Another thing you can do for your skin is to make a simple Vitamin C serum out of ascorbic acid crystals and water. You have to mix this up daily though, as it oxidizes within 24 hours. Vitamin C serum will boost any sun protection you have, plus it is good for the skin anyway.
There ARE natural sunblocks out there, like Aubrey Organics, but you have to apply them every half-hour, a real pain! Plus they don't work as well as the high-tech ones. Again, I'd err on the safe side with alternatives, myself.
Another thing, do not wear fats, oils, or creams of any type on the skin while outside in the sun - they will oxidize and contribute to sun damage on your skin. Save the lubrication for AFTER sun exposure.