Final answer:
A pustule is commonly caused by a bacterial infection and is associated with conditions such as acne, impetigo, and folliculitis.
Step-by-step explanation:
The cause of a pustule is often a bacterial infection. Pustules are small bumps on the skin that are filled with pus, and they commonly occur in conditions such as acne, impetigo, and folliculitis. For example, in acne, clogged pores that are filled with sebum create an environment where bacteria can thrive, leading to infection and inflammation that manifest as pustules. Similarly, the skin condition impetigo, which often presents itself with pustules around the nose and mouth, is caused by bacteria such as Staphylococcus aureus or Streptococcus pyogenes. Folliculitis is another bacterial infection that affects the hair follicles, resulting in itchy, red, and sometimes pus-filled bumps.