From: myron fehr on

There are several things that occur in the skin that can lead to acne
blemishes. Acne occurs when the pores become blocked. The precise
combination of things that can lead to acne are not fully known but
there are several factors that can contribute:
- Genetics- Hormones- Diet- Stress
The way your body deals with dead skin cells and outside things like
climate or other environmental triggers can also be factors.
The pores become clogged when dead skin cells combine with sebum - a
naturally occurring oil in your body. These two things combine to
block the pores, rather than allowing the oil to drain through the
surface of your skin.
Next, bacteria grows around the clogged pores. This leads to your
body's white blood cells attacking the bacteria, fighting to push it
out of your body.
This battle generally takes 2 to 3 weeks to play out, and the growths
that result are called microcomedones. They ultimately turn into
comedones - more commonly known as blemishes, pimples, zits or
acne....

http://groups.google.com/group/acencuredu