system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do drugs like meth and crack change someone's appearance?

Thank you all for your contribution! I will get to upvoting all of you... tomorrow.
gpt
Constriction of blood vessels decreases the amount of blood that reaches parts of the body, and parts that rely on the smallest vessels may not receive enough blood to remain healthy. Skin and the face are two examples, and the mouth is a special case because other regulating systems are also compromised, like saliva. Smoking complicates mouth problems, and injection further compromises the already-suffering skin with wounds, which the body struggles to heal. Not sure about hair, eyes, and nails and stuff.