4 effective ingredients in the fight against acne.

Your teenage years may be long behind you, but the threat of acne still lingers. If you struggle with persistent acne or have oily skin, these ingredients are for you. They help to mattify the skin, unclog pores and remove dead cells and bacteria for a cleaner, brighter complexion, free of whiteheads, blackheads and other imperfections. Start slowly with these powerful ingredients and avoid using them in tandem from the start. What it does: Made from a yeast that occurs naturally on the skin, this exfoliating ingredient reduces hyperpigmentation, fades dark spots and kills the bacteria that cause acne and rosacea. Who it's for: All skin types, but especially acne-prone skin.

How to use it: Twice a day (morning and evening) or once every other day for sensitive skin. Additional information: Start slow – azelaic acid may cause dryness or peeling in application areas. What they do: BHAs are oil-soluble acids that penetrate deep into pores to target sebaceous glands and reduce oil secretion. Who it's for: People with acne-prone and oily skin, as it reduces oil secretion and removes dead cells to prevent breakouts. How to use them: Start with twice-weekly use at a low concentration and increase the strength and frequency as you see they are tolerated by the skin.

Additional information: Although effective on oily skin, they can cause flaking at first, especially on dry or sensitive skin. What it does: A gentle chemical exfoliant, polyhydroxy acid (PHA) removes dead skin cells from the skin's surface for a smoother, more even texture. Who it's for: Gentler, less irritating and more hydrating than its AHA and BHA exfoliating siblings, PHA doesn't penetrate deep into the skin but still exfoliates, making it suitable for sensitive, rosacea or eczema skin. How to use it: PHA pairs well with other active ingredients like vitamin C or retinol – start slowly at first to prevent irritation. Most people can use PHA three or four times a week without problems.

One exception: use once a week if you also use other acids such as AHA or BHA. Additional information: The most common PHAs are gluconolactone, galactose, and lactobionic acid. What it does: A BHA known especially for its exfoliating, pore-cleansing and bacteria-fighting properties. Who it's for: People with oily, acne-prone skin, especially those who want to treat and prevent whiteheads and blackheads. How to use it: Apply as a topical treatment or use a salicylic acid facial cleanser once or twice a week, increasing frequency as tolerated.

Additional Information: This acne powerhouse can irritate sensitive skin or dry out dry skin even more. .