What Causes Bumps Filled With Blood?

My boyfriend keeps getting these pimple looking bumps that when he pops them, blood comes out. He recently got one on his neck and after he popped it, a pink ring seems surround the affected area, what can this possibly be? He has gotten one on his thigh, arm, and now neck. Please help, I am really concerned and afraid that it might be a more serious manner than what he thinks it is.