Good news for teenagers with bad breath: It's usually caused by bacteria in your mouth. Doesn’t sound like good news?  It is, because it means you can take some simple steps to improve your breath. Brush your teeth twice a day for at least two minutes each time.  Floss daily to rid your mouth of the bits of food that attract bacteria between teeth.  Also brush your tongue to remove the bacteria that gather there. You may also choose to use an antiseptic mouthwash.

If none of this works, your bad breath may be caused by something other than bacteria. See your doctor to rule out any medical problems.

The chewing process can help stimulate saliva, which keeps your mouth cleaner.  Chewing sugarless gum helps stimulate saliva, while chewing celery, carrots or other crunchy vegetables also can help clear away loose food particles as well as stimulating your salivary glands.

Shaving has no effect on the rate of a hair's growth, and it doesn't make hair grow back any thicker.  However, it can sometimes make hair appear to be thicker because shaving cuts the hair shaft at a blunt edge. This gives hair a more course appearance and makes regrowth more obvious.

Shave in the same direction that your hair grows to avoid irritation and get a closer, smoother shave.  Other tips for a smoother shave: Wet your face before you shave with hot or warm water or shave immediately after you shower; shave the smoother parts first, then come back to concentrate on the trickier areas, such as your upper lip, chin, and neck; and use shaving gel.

Your hair's oils are important for your hair, but they can be a problem for your skin.  Shampooing daily can reduce the likelihood that hair oils will be transferred to your face, where they can clog pores and contribute to acne.

Benzoyl peroxide, one of the most common over-the-counter medicines for acne, is often very effective.  Other helpful ingredients found in many over-the-counter products include salicylic acid, alpha-hydroxy acids, resorcinol, and sulfur.  If none of these works, see a dermatologist.

Beware the many myths about acne: Chocolate and greasy foods don’t cause it, and sunlight can't clear it up. 

Home surgery is not recommended for pimples.  Squeezing, popping, or lancing a blemish risks pushing the infected material deeper into your skin -- which could create an even bigger eyesore, create a more serious infection, and possibly cause permanent scarring or discoloration of the skin.  Stick to recommended medications or see a dermatologist.

The best way to prevent body odor is to bathe or shower every day to wash away the bacteria that are the source of most body odor.  Antiperspirants can help cut down on body odor by blocking or drying up your perspiration, and deodorants and colognes can help cover up your body odor with another fragrance.  But there's no substitute for daily showers or baths.

Hormones kick in at puberty that stimulate your sweat glands to produce more perspiration.  Because you sweat more, your skin attracts more of the bacteria that cause most body odor.

Jock itch is caused by a fungus, called tinea, that thrives in damp, dirty environments. Your best defense is to shower or bathe regularly, making sure to dry yourself off completely. Wearing loose-fitting clothing also can help, so that moisture doesn't build up between your clothing and your skin.

Tinea, sometimes known as ringworm (though it isn't a worm), is the same fungus that causes athlete's foot. Athlete’s foot is commonly accompanied by jock itch and fungal infection of the nails.  Any step you take to avoid athlete's foot, such as wearing sandals in public bathing areas, where the fungus may have been left behind by someone else, also can help prevent jock itch.

You can't "catch" dandruff from sharing a comb or a brush.  Dandruff  is really a catch-all term referring to flakes of skin that are shed from your scalp. It can have many causes, but none of them is contagious.  In teens, it often results from a skin condition called seborrheic dermatitis, or seborrhea. Most causes of dandruff usually respond to treatment with over-the-counter dandruff shampoos.  More severe cases may require a prescription.

The very end or tip of a hair shaft is prone to damage and splitting -- so-called "split ends."  Blow-drying or too-frequent brushing or combing can actually cause this damage.  But regular haircuts rid your hair of the damaged tip, leaving your hair looking healthier.

Ingrown toenails can be caused by ill-fitting shoes or toe injuries, but they are most commonly the consequence of a nail that has been trimmed too close to the skin.  This allows the skin to cover the nail, and when the nail grows back, it grows back under the skin.

To avoid ingrown toenails, avoid trimming your nails too close to the skin and keep them trimmed in a straight line across the toe rather than rounded at the edges.  This reduces the chance they will grow back ingrown.

Dermatologists caution acne patients against using products that can irritate the skin -- including ordinary astringents, toners, and exfoliators that contain scrubbing particles.  Instead, simply wash your face twice a day with soap and warm water or use a product containing an ingredient used to treat acne, such as benzoyl peroxide or salicylic acid.

Stress can be the enemy of your appearance in many ways.  It's been shown to cause flare-ups of both dandruff and eczema, a common skin problem marked itchy and inflamed skin. While stress doesn't "cause" acne, it can make it worse.  Overall, stress makes it more challenging to maintain good grooming.  If you're a teenager, you face plenty of stress and you have a lifetime of stress ahead of you. If you start learning stress reduction techniques now, you'll not only feel better, you'll look better.