Here is something I picked up for a site:
"Chances are if you have acne troubles then you have experienced acne just about everywhere, including your chest, neck, back, and face. Many people are wondering what causes sudden chest pimples to form. There are many different causes for acne and there is no one answer as to why it occurs. Everyone has different types of skin as well as acne, and for each kind of acne there tends to be a different explanation as to why it occurs.
Acne does seem to come on very suddenly, which is one of the most terrible things about it. One day your skin is clear and beautiful and the next day you are covered in pimples. One of the best explanations I can offer is that acne occurs most of the time as a result of too much oil entering the thousands of tiny pores found in the skin at one time. When that oil becomes too much for the skin to handle, acne forms on the surface of the skin.
So what causes all that oil to form in the body? Most of the time it is caused by a hormonal imbalance. This hormonal imbalance is common among teenagers and most pregnant women. When a woman becomes pregnant her body's hormone levels fluctuate very frequently, causing the oils in the skin to secrete and go into the pores, clogging up all up. This is why you see many acne treatment products advertising pore exfoliating agents which unclog the pores in the skin and treat your acne. There are other possible causes for acne such as poor hygiene or diet, but these are just theories. A hormonal imbalance in the body is the one and only sound explanation as of right now even though there are many different people who speculate that there are more than just one cause for it to occur."
