A topical medication used to reduce oiliness and remove skin cells that cause pore blockages. Sulfur helps clear the skin of comedones. Besides treating acne, it is also used to improve other skin conditions.
Sulfur can be found in both over-the-counter and prescription medications, often along with other acne-fighting ingredients like resorcinol or sulfacetamide.
Side effects include drying of the skin, peeling, redness, burning or irritation. Sulfur itself has an odd, "rotten egg" like odor, but most of today's products don't smell too bad.
One of the oldest known acne medications, sulfur has been used to skin problems for thousands of years.

