How much damage does a keratin treatment cause hair?

Of course, an incorrect procedure can damage the hair, but directly straightening itself can not cause its indiscriminate loss. But there is a tech who assures this, and, in their opinion, everything goes in stages:

Hair absorbs protein, after which it becomes heavier;

In fact, keratin strengthens the hair itself, and this is a laboratory-confirmed fact. In addition, the hair can not be weighed down with a cosmetic product so that it falls out on its own. By the way, wet hair is three times heavier than dry hair, and how many times a week do you wash your hair?

Keratin straightening also has no effect on the hair follicles. After all, keratin itself is applied to the hair, not to the skin. Hair can fall out due to climate change, a recent severe illness, malnutrition or even severe stress that happened three months ago.