Recently, I had a large, painful, red and white pimple on my left breast, and I popped it. I would like to know what it was. Can you help me?

It is difficult to diagnose a skin issue without seeing it in person. However, based on the description provided, it sounds like the presence of a boil is likely. If this is the first time you have experienced this, there may not be cause for major concern. Keep an eye on your skin to see if any similar issues occur in the future. It is normal for the area around a boil to appear red and swollen, as the body sends blood and white blood cells to the site to help fight off any infection.