It's the morning of your big event. You wake up excited, nervous and ready for anything--except the large red bump on your face. Why do pimples always pick the worst time to appear? Knowing what causes them and what to expect from them will give you the ammunition you need to keep them in line...and off of your face.

There are several kinds of blemishes--all precursors to acne.

A whitehead occurs when a pore gets clogged, then closes and bulges out. If the pore is clogged but doesn't close up and the opening turns dark, that is a blackhead.

A damaged pore that becomes infected will result in a little red bump, or pimple.

All of these, if left untreated, can lead to acne.

Skin blemishes are caused by a hormonal changes that result in oily skin, clogged pores and infection. Stress is a large factor in causing skin problems, but--contrary to popular belief--blemishes are not caused by eating chocolate or greasy foods.

Some people have reported that certain foods seemed to make their skin worse. Though there have been no clinical studies to support this, common sense dictates that if you seem to see a connection between foods and pimples, you should avoid those foods.

When humans reach puberty, their skin thickens. In addition, teenagers (and women who are menstruating) increase production of hormones, which releases DHT, a hormone by-product. DHT makes the oil-producing gland go a little crazy. This over-production of skin oil--called sebum--can clog the pores.

It can take two to three weeks between the time your pores get clogged and the time acne shows up, so prevention is key.

If the walls of a pore are damaged or weakened, dead skin and a bacteria called Propionibacterium acnes (P. acnes) can get stuck inside the pore, beneath the skin. This will cause an infection that results in the little red bumps we know as pimples.

Pimples usually announce their presence with itching before the actual eruption occurs. Treat the infection at this stage with cleansers and moisturizers specifically designed to treat outbreaks and you can often prevent the pimple from erupting altogether.

Inflammation--the redness and swelling--is caused by your body's white blood cells attempting to fight off the infection caused by the P. acnes bacteria trapped inside the clogged pores.

It can take as long as eight weeks from the time the infection first occurs until the pimple clears up, so daily skin care is very important. Hard scrubbing and exfoliating will only irritate problem skin, so be gentle.