There are plenty of things that play enemy to your skin, cause it to break out in acne, discoloration, redness, big pores, etc.  Even when you are past the stages of normally getting acne, these things can still continue to sabotage your skin and cause serious issues among other things.  First of all, of course stress is one of your biggest enemies.  It causes the glands to produce more sebum, react to more things, and it breaks down the skin’s basic defenses.  It actually messes with the hormones.  Next in line is the sun.  It creates more skin cell breakdown, reduces the skin’s basic defenses, and otherwise makes it harder for your skin to function in a normal way to say the least.  This actually causes skin cancer, premature aging, and other various problems.  It does provide vitamin D.  But realistically you should be getting your vitamin D out of your food as it obviously does not come with all the problems, side effects, and risks.  Plus the sun really doesn’t provide that much vitamin D to be quite honest.  And finally there is aging. The skin acts as a barrier to the outside world and all its harmful elements.  As you age, your skin thins, it breaks down, and it is less able to actually protect your body along with obviously looking worse.  So among others, these are the 3 big vices.