Hair straightening can basically be classified as:

1. Restructuring of Hydrogen bonds - blowdrying & ironing - effect last few hours to days.

2. Introducing new amino acids into the hair structure and increasing it’s porosity - effects last a few months.

3. Breaking the disulfide bonds and restructuring them - permanent chemical straightening - effects lasts permanently till hair grow out/are cut.

Keratin hair treatment is a temporary hair straightening procedure. Benefits of it include lesser entangling of hair after the procedure. Makes the hair smoother and straighter, temporarily for upto 6 months. It is said that the structure of the hair proteins is maintained, but made porous due to the chemicals used in the keratin treatment. They are a mashup of various amino acids, and formaldehyde is often used to help in this process of fusing the external amino acids to keratin and increase the porosity of hair protein structure. They apply the chemical, let it seep into the hair, blow dry the hair, again apply the chemical, and them set it with a low-mid level heat of flat iron. 

The chemicals applied do not actually contain keratin. It is also commonly known as brazilian blowout procedure vis a vis Permanent Chemical Straightening where the chemicals used (lithium hydroxide, sodium hydroxide guanidine hydroxide, ammonium thioglycolate etc) break the hair structure permanently (by breaking the disulfide bonds) and restructure it to become straight. So the hair remains straight until it grows out or is cut.Cysteine hair treatment has more smoothening effect, less straightening effect, as compared to keratin treatment. The steps involved in doing it are very similar to the keratin treatment, but different chemicals are used. Apparently lesser strength of chemicals in cysteine treatment.Very temporary short treatments done at home to make hair straight include ironing the hair and blow drying. These are temporary because instead of breaking the disulfide bond, these just rearrange the hydrogen bonds in the fibre. The hydrogen bonds return back to their original structure within hours or days. Water immediately nullifies the effect of a blowdry or ironing. People are really happy about the results and love the way the hair feels after doing them. Hair become a lot easier to handle.