Keratin treatments can transform hard-to-style hair into sleek and manageable tresses. After treatment, hair is visibly less frizzy and can be blown and flat ironed in half the time. While this treatment may seem miraculous, it only applies to the hair you already have.
Keratin treatments aren't permanent. They last anywhere from one to four months. Since your new hair won't have been chemically straightened, it will grow as your natural hair texture. However, you shouldn't see an unsightly line of demarcation. As keratin treatments only last a few months, by the time a significant amount of new hair has come in, your keratin treatment will have worn off anyway.
Speeding Along the Process
If you'd rather not have a combination of natural hair and keratin-treated hair, the type of shampoo you use can help. Shampoos with sulfates strip keratin from hair. Typically, it's recommended to only lather up with sulfate-free shampoos to make your treatment last longer. However, if you're ready to go back to your natural texture, a change of shampoo will do the trick.
On average, human hair grows at a rate of 1/3 to 1/2 inch per month. By the time your keratin treatment has started to wear off, your hair would have grown anywhere from 1/3 to 2 inches and, since keratin treatments can be reapplied once per month, it's simple to keep your texture consistent from root to tip.
If you're still concerned, pick a different smoothing method. Deep conditioning your hair can actually make it more manageable, as hydrated hair is less prone to frizz. Some shampoos and conditioners come with keratin built in. These products aren't as effective as an in-salon keratin treatment, but they do help to strengthen strands. Another option is going to a salon for a blowout, which will keep your hair sleek and straight until your next wash.