For example Global Keratin has four different compositions which are

Keratin Hair Treatment with 2% Formaldehyde works great on colored, bleached, relaxed and highlighted hair. It will make your hair soft, shiny, healthy and straight (straight 100% if your hair is not extremely curly or virgin). It is recommended for all hair types.

Keratin Hair Treatment with 4% Formaldehyde is recommended for virgin, very curly and afro hair. The additional Formaldehyde content will make your hair totally straight, sleek and conditioned. However this product is not suggested unless your hair is extremely curly or virgin and curly.

For those preferring to stay away from formaldehyde there is a Formaldehyde Free product. This treatment absolutely does not contain Formaldehyde. It is suitable for clients who are looking to soften their curls or waves and make their hair healthy and shiny. Depending on the hair type it will also provide some straightening. However it works best on previously chemically treated hair. This treatment is formulated with keratin complex and Silica which act with high effectiveness to leave the hair lustrous, manageable and hydrated.

Lastly there is also a Keep the Curl treatment. This product does not contain formaldehyde and does not straighten the hair. It is recommended for people who want to keep their curl but close the cuticles. In general it keeps the hair healthy.

so based on your needs you can choose the product. Remember to use keratin based shampoos and conditioners after the treatment. they should be essentially sodium chloride free to increase the longevity of the treatment.

Checkout Global Keratin’s line of effective aftercare products like deep conditioner and clarifying shampoo.

Keratin in general is the primary protein of hair and it will not cause hair breakage. It will only make it healthy and strong.