What Can Cause White Bumps On Torso And Under Arms?

My 5 yr old son has a number of white bumps coming up on his torso and under his arms that are quite solid to the touch and luck like they might be filled with white pus. They don't seem to bother him too much, but ever now and again, one becomes very sore and bursts then goes away leaving a bit of a scar. The skin around them can become quite red and dry, too.