system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What are dissolvable stitches made of and why aren't they used in every medical procedure?
gpt
What are they made of? One of the most common are "catgut" stitches (more correctly called sutures) which are made from processed products that come from the intestines of sheep/cows (despite the having "cat" in the name). Others are synthetic (made using chemical processes) polymers (plastics are examples of polymers) that, unlike many familiar plastics, slowly disintegrate when exposed to the body.  

Why not use them in every procedure? As these sutures dissolve they progressively lose their strength. In some situations the doctor (and patient!) really does *not* want the stitches to fail. E.g. someone having surgery on their intestines might have a large cut down the middle of their abdomen. It is obviously undesirable for a patient's gut to burst open and spill their intestines onto the floor when they squat down or try to pick up a heavy object. Better to just remove the sutures manually when certain that the wound has healed enough to hold on its own. Other examples are heart surgery where again it is very undesirable for the sutures to give way so maximum security is preferred.