My friend one day stopped eating meat in fear of it not being cooked, now checks expiration dates on all foods & is obsessed with foods being out of date or undercooked. is there a disorder that causes this, what causes it & what treatments can help?

Checking food dates: This may just be someone who is very safety conscious. What you described doesn't sound like a disorder. Now, if the person is so involved with these thoughts and behaviors that it is negatively impacting multiple areas of life that might (did you see that I said "might") be obsessive compulsive behavior. I certainly would not want someone to be labeled with so little info.