How often can you do a keratin treatment?

[Polly]

I had a keratin treatment done in June. I have fine, frizzy hair. It's getting frizzy again. My hair is already in not great condition since I took out my extensions in June but getting slightly better now. Should I get another keratin treatment now or wait a while?

[Sur La Mer]

They last about 2-3 months.

I do not recommend them.
Hair straighteners are known as hair relaxers, keratin treatments and hair-smoothing products. They work by breaking and reforming the chemical bonds in keratin, which is the main protein that gives shape to each hair.

> > > > BRAZILIAN BLOWOUT HAD BEEN BANNED by the Food & Drug Adm. Sept. 12, 2011.

Google: keratin treatment warnings. About 2,620,000 results (0.36 seconds) 6-24-12.
 1-23-12. and Google: Lawsuits Brazilian Blowouts. About 1,010,000 results (0.24 seconds) 
In Sept. the federal government put out a hazard alert about the hair-smoothing treatment, Brazilian Blowout etc. warning that it contains liquid formaldehyde that can turn into formaldehyde gas when heated during a treatment. Now, the company's bottles of solution carry a warning label to alert stylists to the potential formaldehyde risk and the need to perform the treatment in a well-ventilated area. The manufacturer said Monday (3-6-12) that it had agreed to settle a class-action lawsuit for about $4.5 million.

Hair-straightening products are allowed to contain small concentrations of formaldehyde (0.2 percent). But several hair-straightening solutions have been found to contain well above the allowable limit. For example, one popular hair-straightening product that advertised itself as “formaldehyde-free” actually contained 6.8 percent to 11.8 percent formaldehyde.
Another example: Fourteen women, including two from North Texas and one from Houston, are suing Unilever, the maker of a product they claim caused permanent damage to their hair.
"It transforms frizzy, unmanageable hair into hair that's sleeker and easier to style," said the commercial for the Suave Professionals Keratin Infusion 30-Day Smoothing Kit, which is no longer being sold
When she began looking online for more information about the product, she said she found some people who said it worked, but more who said it damaged their hair.
She discovered a Facebook page devoted to angry consumers, and there are multiple postings on YouTube. I've been warning people about relaxers since 2009 and people are giving me thumbs down!
BTW: A variety of hair-straightening products used in professional salons can expose both hairdressers and their customers to formaldehyde. The results show that three professional hair-smoothing treatments labeled "formaldehyde free" can produce the cancer-causing chemical at concentrations above the occupational exposure limits set by the Occupational Safety and Health Administration. They tested four products: Coppola Keratin Complex Blonde Formula, Global Keratin Juvexin Optimized Functional Keratin, La Brasiliana Escluso Keratin Treatment with Collagen, and Brazilian Blowout Acai Professional Smoothing Solution. While ChemRisk tested four popular brands of hair straighteners, THERE ARE HUNDREDS on the market. Nov. 11-11

By contrast, beauty salon owners and stylists generally lack a scientific background and don't have a keen awareness of the danger of working with products that contain formaldehyde, experts say.

Watch: Good Hair a documentary by Chris Rock 2009 on BET or HBO. According to Tyra Banks, 80% of the black population are part of the billion dollar hair industry. Clips on youtube videos, also.

Chemicals can enter the body through the skin.

Sources:
Google FDA.gov & search for Hair Dye & Relaxers.
Google: Hair Dye FAQ's Are Hair Dyes Safe?