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No, it's not a new styling product -- sebum is the oil your skin produces to keep everything moisturized and protected. If you've ever experienced greasy skin -- bam, you've had sebum buildup. While getting rid of sebum buildup may seem obvious (wash it away, duh), you have to cleanse correctly to remove the buildup without stripping your skin too clean. Basically, you have to preserve that delicate balance between too much sebum, which can cause acne, and too little sebum, which can cause dry skin.
Turn on the warm water in the sink -- warm, not lukewarm. Splash your face several times, enough so that your entire face is dripping wet. Pump a few drops of facial cleanser in your clean palm and work it into a lather. (You can use any oil-free facial cleanser you prefer.)
Massage the cleanser over your entire face, using small, circular motions. Take your time applying the cleanser, and make sure you cover every inch of your face. Rinse your hands in the warm water. Splash your face with water until every drop of cleanser is rinsed away.
Gently pat your face dry with a towel. Relax and do a few neck rolls as you give your face a minute to breathe in the air. Pour a little astringent onto a cotton ball. Wipe your face clean, especially your nose, adding more astringent as needed. The astringent will remove any remaining residue and help tighten pores.
If you have problems with oily skin during the day, use a little astringent to clear up any problem areas. If your skin is too sensitive for astringent, or you don't want to mess up your makeup, use some of those amazing blotting papers. Assorted "anti-shine" cosmetic papers pull away oil without removing too much foundation; some of them pull away oil while adding a light coat of foundation powder.
Sebum buildup can be especially bad around your nose, which is what causes annoying blackheads. If you're looking for a quick fix, you can try a pore strip to pluck the blackheads from your skin. However, people with sensitive skin or skin easily prone to spider veins should never use pore strips; you'll end up looking like Rudolph. Gentle exfoliation and regular cleansing are the best bet to fighting blackheads over the long term, sensitive skin or not.
Avoid using moisturizing or oil-based cleansers if you have oily skin and sebum buildup; stick with water-based cleansers to really clear away the sebum.
Cleansers that contain salicylic acid or benzoyl peroxide can help dry out your skin to reduce sebum levels.