I have blood blisters or boils on my chest. they hurt especially when you touch it. i have dark spots from old ones. how do i get rid and prevent them?

Abscesses?: Abscesses, boils, small carbuncles, etc. or whatever they may be called are very tough to treat and are often caused by underlying bacterial skin infections that occur locally and can "come and go." As you desribed, they may leave scars or marks where they were. See a Dr. for an exam as sometimes daily antibiotic treatment for suppression may be helpful, etc. Best wishes.