Sometimes, acne can result in the formation of pus filled pimples. Pus is a thick yellow fluid produced as a result of the immune response of the body to certain infections. It consists of macrophages and bacterial cells. In case of acne, the pores get clogged with dirt, oil and debris. This creates an environment perfect for the growth of bacteria. The immune system of the body counters this infection by recruiting macrophages and monocytes to the affected region. They accumulate in the form of pus. Pus filled cysts can be deep and painful since the infection and inflammation can run deep within the skin, to surrounding tissues. Pus filled acne is the more severe form of acne. It can leave deep scars too. If you find that you have pus filled pimples on your face, the best thing to do it to leave it alone. Frequently touching the pimple can cause infection to spread to other parts of the skin. Popping or bursting the pimple can also cause infection to spread. It also causes the formation of deep scars. In most cases, your body will fight the infection on its own and the condition will disappear within a few days or weeks. You can help by applying a warm compress over the pimples and then applying a mild antiseptic. If the pimples do not clear up on their own after some time, visit a dermatologist.