Acne strikes 80% of teenagers due to hormonal changes. In boys it is the androgen and in girls the estrogen that leads to an oversupply of sebum, a substance that keeps the skin oily but in an oversupply tends to clog up the pores.
The pores may also become infected with Propionibacterium acnes which feed on the oil in the pores and may lead to skin infection.

All of the herbs mentioned above are effective. Licorice root, Sassafras and Saw Palmetto are a good combination.
Herbal remedies must go hand in hand with a change in diet. Saturated fats should be replaced with fats from Flax, Olive, Sesame and similar Oils. Make sure enough fiber is added, such as Psylium husks or Flax seeds.
Vitamin B6 (Pyridoxine) can help in regulating a hormonal factor, especially in women with premenstrual aggravation of Acne*.

Avoid: Chocolates, nuts, greasy fast food, milk (unless skimmed), refined carbohydrates, trans fats, hydrogenated oils, large amounts of salt (because of its iodine) and seaweed.

The following may cause or aggravate Acne:
1. Drugs*: Bromides**, Corticosteroids, Diphenylhyantoin, Halogens, Isonicotinic acid and Lithium carbonate.
2. Chemicals*: Cosmetics, Coal tar and derivatives, Chlorinated hydrocarbons, Machine oils, Pomades, Over-washing, Over-rubbing.
3. Food items*: Milk products, Saturated fats, Trans fats, High iodine content, Sugar.

Washing the face and other affected areas with soap and warm water will drain some oil and help in milder cases.
An Over-The-Counter treatment recommends Benzoyl peroxide which will help to clear the pores but may also create red skin with a stinging or burning sensation.
Salicylic acid has been used to remove the top layer of the skin.

When bacteria is involved (infection and inflammatory response) Tea Tree oil has shown results which were comparable to Benzoyl peroxide (with less side-effects)*. However, Tea Tree oil may also cause Contact Dermatitis to those who are allergic to it.
Azelaic acid is available in creams and has shown to be an effective antibiotic in the treatment of Acne.

Regular timed exposure to sunlight may also help.
Prescription treatment may include antibiotics.
There are reports that in some cases Insulin treatment has been successful.

For Acne conglobata (Cystic acne) the cysts may occur so deep in the skin that they may have to be opened by incision or puncturing. Whatever the procedure, the area has to be wiped down first with an alcohol swab or hydrogen peroxide (3%), the equipment must be sterile and no open wound should be touched with fingers.

Sources:
* Textbook of Natural Medicine, 2006.
** The Condensed Encyclopedia of Healing Foods, 2006.