What's the difference between acne and sebaceous cysts?

Not always different: Sebaceous glands are the organ that is involved in acne disease either when they become inflamed or infected. Sebaceous cysts are sebaceous glands that have become obstructed and develop into large cysts filled with keratinous material. They do not necessarily become inflammed or infected and may remain quiescent. One form of disease is called cystic acne and is characterized by inflammed cysts.

A great deal: Acne is generally an infection within an oil gland, hair follicle, or a blocked pore. The oil within that gland is blocked, becomes rancid, and then infected usually by a specific bacteria. It can be treated very effectively with good medical topical treatment. A sebaceous cyst is also blocked but not necessarily infected and cannot be treated with creams. See an experienced skin expert.