Cystic acne is a common problem recognized by whitehead and blackheads on any part of the body.  Acne has mild, moderate, and severe levels of course, and many have mild to moderate acne, most have that in fact.  But cystic acne is essentially speaking one that turns into large bumps without a head, unlike whiteheads in so many ways.  These large bumps contain pus and as always it is important to leave them alone. 

If you try to squeeze them, you will only cause more inflammation and irritation and scarring in the end, which is definitely not a pretty thing for many individuals.  For some, it will be worse than it will be for others of course, and they can be ongoing and cause quite painful distress in general.  A poor diet is generally recognized to contribute to these particular cysts as is the lack of acne treatment in general.  There are quite a few contributing factors that are currently considered, but there are no known actual causes as with any type of acne.  The best way to deal with some of it is to find a good generalized acne treatment and it will get to the root of that problem in many ways too if it is doing its job correctly of course.