What are papules? When the skin becomes very irritated the walls break down. They cause large abnormal skin tissue to form called papules.  They are hard often 1 centimeter in size and different shapes. They are called lesions. The other type of acne is pustules. Pustules are filled with pus and often yellowish in color. They resemble a blister or cyst. When you have these conditions you need to see a dermatologist.