Tanning does, utimitaly thicken the skin giving it the leather look over time.. however many other factors are involved with it's intensity, such as genetics and whatnot.
I have been tanning for years. I do not burn hardly ever (and certainly not intentionally). I wear lotions inside and ALWAYS sunscreen when at the beach.
SunBURNS are the real culprit when it comes to cancers. Burns have deep penetrating rays that reach past the dermal layer of the skin, warp the cell's DNA which, over time can create the tumors you see as cancers. A tan is the bodie's natural depfense to prevent the rays from penetrating far enough to burn, which will happen when your skin does not have enough melanin to release to block the intensity of the rays.
I tan (lightly). My parents both tanned nicely.. my mother actually used to fry in the sun back in the day using margerine (when butter got too expensive lol).. but I don't recommend than
They both sill look pretty good, I know I have genetics to not look too much like a hag.
Also consider the other things that go into looking like a hag besides tanning.. smoking, heavy drinking, obesity and, of course bad eating (if you've ever seen an eposide of "honey we're killing the kids" you'll know what i mean).
OK, I don't want to sound like im endorsing tanning here
I don't see anything too bad about a light tan as long as you don't have cancer in your bloodline and you take measures to prevent burning.
SunBLOCK will be better at blocking BOTH rays of the sun, SunSCREEN is good for those like me that do not want to burn, but do not want to sit at the beach all day and not get a light tan.
The SPF you use can be determined by the level of your skin, the burning ability you have and how long you plan to be in the sun.
If you are fair and burn easily, you would want a very high SPF. Believe it or not a lot of sunscreens aren't designed to renew themselves just by being reapplied, they have to be washed off or they lose their potency and the SPF drops. This is why a lot of times you can still burn even when reapplying regularily.
On the flip side if you tan easily and burn rarely you can tolerate a little tan and less sunscreen. I go to he beach and use SPF 4. I tan just a little and don't burn. My cousins on the other hand, we went to the shore last summer and I was dousing them with SPORT SPF 50 every hour when they fell asleep on the beach and they STILL got FRIED! They have no melanin and their skin is translucent. I barely got a tan at all that day and I didn't put the SS on for a good hour.
So your predisposure to sun tans, burns and damage and the level to which you will experience them is genetics (both their parents were pale).
I wouldn't stress if you get a little tan, as long as you like it and it doesn't burn. If you do not want any tan at all then use SUNBLOCK. Just remember that without any tan a all your skin will have no defense against the sun ands if you are out for the picnic, poolparty or at the beach you will be VERY vulnerable to the burning process.. and remembe rthat you burn much easier in the water
Oh.. and "water proof" only means that it will protect you for a while in the water.. it still need to be reapplied regularily when in the water or reapply after intense sweating.
Got a little off topic sorry.. hope it helps!