I found out that collagen is haram to consume especially because it is most likely to be from a pig. But what about collagen in shampoo?
Pig-derived collagen would be impure (najis). Consider consulting the manufacturer, as your shampoo may not be derived from pigs.
In the following fatwa, the hydrolyzation process was considered an insufficient transformation to change this status in the context of creams and lotions:
Hydrolyzed collagen is produced from collagen found in the bones, skin, and connective tissue of animals such as cattle, fish, horses, pigs, and rabbits. The process of hydrolysis involves breaking down the molecular bonds between individual collagen strands using heat and either acid or alkali solutions. (www.naturalpigments.com)
Hydrolyzed collagen will have the same ruling as gelatine, therefore, if the gelatine is derived from haraam sources namely pigs or any other animal upon which Allah’s name has not been mentioned, it is not permissible to use it.
Mohammed Tosir Miah, Darul Ifta Birmingham, 2012 fatwa
Assuming the shampoo is impure, the question now becomes: is it halal to use impure shampoo?
Islam Q&A says no:
The materials which are used to manufacture... shampoos... ...[if] it comes from animals whose meat and fat are forbidden to eat, such as pigs... it is haraam, with no doubt.
but with the caveat:
...the basic principle with regard to such things is that they are taahir (pure) and it is permissible to use them, until it is proven from a trustworthy source that they are mixed with pork fat or some similar impure substance which it is haraam to use. In that case it is haraam to use them. But if the news is no more than a rumour and is not proven, then it is not obligatory to avoid using it.
Likewise, a IslamWeb fatwa discussing shampoo containing alcohol:
...it is not permissible to benefit from an impurity