What happens to teens with extreme, untreated, ignored stress?

If a teenager of fifteen is under extreme stress to the point he has large, dark circles under his eyes and is not taken to any sort of specialist, what would be expected he might do that normally he wouldn’t consider doing? That is, are there any kinds of probable illnesses or behaviors on his part as a result of long-term, unavoidable stress? The “mother” in question refuses to deal with it fearing that she might encounter problems with Child Protective Services.