...thermal reconditioning (also called Japanese straightening) is best for bulky, loose to medium—but not kinky—curls. The hair is saturated with a solution containing a chemical that breaks the bonds that give each strand its shape; it is then rinsed, blow-dried, and meticulously flatironed. Once a neutralizer is applied, the hair is locked into this new, straight configuration. The process can take up to eight hours the first time (depending on length and thickness); touch-ups require three to four hours. For three days after the treatment, you can't get your hair wet or do anything kink inducing (like wear a ponytail), and while your hair will now be sleek and shiny (even after air-drying), you're left with one styling option: bone-straight. Even curling irons or hot rollers won't restore volume or wave. Cost: $500 to $1,500.
...a relaxer can soften coarse, tight curls; it uses strong chemical compounds that break various bonds in the hair. The solution is left on for up to 20 minutes, rinsed, then neutralized. Cost: $50 to $250.
Keep in mind that...since both of these treatments permanently change the structure of the hair, you have to continue them or endure a grow-out period. They contain damaging chemicals, so don't consider either one if your hair is already overprocessed. Tell the stylist everything you've done to your hair in the past two years—bleach and some hennas don't react well with the chemical in thermal reconditioning solutions, and colored hair may be too fragile to handle a relaxer, which is particularly harsh.
If you want something that wears off over two to four months...
...some treatments, like Brazilian straightening (brand names include Brazilian Keratin Treatment and Brazilian Blowout) and Keratin Complex Hair Therapy, smooth the surface of the hair but don't permanently break bonds, so your natural texture gradually returns. The Brazilian treatments, however, have been shown to contain varying amounts of formaldehyde (a carcinogen that poses health risks when inhaled), in addition to keratin protein. The makers of Keratin Complex Hair Therapy say their product uses a "captured form of formaldehyde," and that any formaldehyde gas released during the treatment is below the exposure limit set by the Occupational Safety & Health Administration. (Stylists attest that it does not have the noxious odor of the Brazilian treatments, but independent testing has not demonstrated how much formaldehyde is released during use.) After the product is applied, the hair is blow-dried, then flatironed; the solution stays in the hair until you shampoo three to four days later. These treatments can be done on color-treated hair and are effective on everything from waves to tight curls; they control frizz but maintain some texture and volume. Though you'll still need to blow-dry hair straight, the process will require less effort. Cost: $300 to $600.
Keep in mind that...a treatment containing formaldehyde could compromise your health.
If you want something that will smooth your hair until your next shampoo...
...a deep conditioner controls frizz by restoring moisture to the hair. Work the product from roots to ends, and slip on a plastic shower cap for 10 minutes (it traps heat from your scalp and helps conditioners penetrate the hair's cuticle), then rinse. No marathon salon visits or grow-out period necessary. Cost: $5 to $50 (for a tub of conditioner).