Keratin is a type of fibrous structural protein.
That doesn’t sound exciting, but it’s often added to shampoos and hair products in order to repair damaged hair, and sometimes keep hair straight.
The sad thing is that most keratin comes from ground up animal hair, horns, hooves, and feathers.
The vast majority of keratin is not vegan.
It is possible to make vegan keratin.
It can be synthesized from amino acids extracted from plants.
Technically the outer layer of human skin also has keratin in it, but I haven’t heard of any products being made using that source (maybe that’s gross).
Regardless, keratin is not vegan under normal situations. If it comes from a plant-source, the product will make it very clear on the label and ingredients that it’s “vegan keratin.”