It doesn't sound like these kids are sick, rather they just think their skin looks a bit different. My guess is things have gotten cold, they've cranked the furnace up at school, the humidity is dropping and everyone's skin is getting dried out. Stir in school phobia and routine teen hysteria and you've got an epidemic. I had a girl this age in yesterday, a safe distance from the Washington Post here in Iowa, with similar complaints. Objectively she was very unimpressive, just dry skin and a bit of keratosis pilaris (small uniform scaly bumps at hair follicles which are sometimes a bit red), which can be aggravated by dry skin. KP is very common but non-dermatologists possess great ignorance of it. It is generally ignored by everyone except hyper-observant (i.e. normal) kids.
I was having fun vomiting up 4 slices of pizza while I was trying to think; not a good idea.