Hello and welcome to HCM.
After going through brief history we can not make out the best possible diagnosis as you have not mentioned your age, from how long they are there, what is the exact size that these bumps (as actually what extent these grow up to ) and are these sometimes present on other areas such as face. Even then we can make out best possible diagnosis:
vulagaris: A simple youth related problem due to blockage in a sebaceous gland(produce oil in the skin). These comes and goes in youth period and some times form cystic structures as you have mentioned. Can take simple treatment for acne to resolve the condition.
2.Trunk folliculitis: Small papular and pustular folliculitic eruption on the trunk of young and middle-aged adults. Can be sometimes be of fungal origin.
3. Multiple sebaceous cysts: Collection of cheesy material in oil glands without any other sign and symptoms. May get enlarged or inflamed sometimes.
Whatever be the condition it you can get that these are not bothersome condition. The only thing which you have to remember is not to squeeze or pinch or express any of the lesion over chest otherwise can lead to keloid formation which is definitely a problematic situation.
For the best of thing can meet a dermatologist
for diagnosis and treatment.
Hope to have given you the best of the information.
With best health wishes,
Dr Sanjay K Kanodia
MD ( Dermatology and STD/ Venereology)