Final answer:
A bulla is a large fluid-filled blister that measures at least 5 mm in diameter, commonly associated with bullous impetigo, a skin infection that results in the formation of these blisters, particularly around the nose and mouth.
Step-by-step explanation:
A bulla is a large, fluid-filled blister that has a diameter of at least 5 mm. In the context of skin infections such as impetigo, bullae can form and rupture, leading to encrusted, draining lesions. Impetigo, specifically bullous impetigo, is one condition known for the formation of bullae, often around the nose and mouth. These are commonly caused by bacteria like Staphylococcus aureus or Streptococcus pyogenes, and the infection comes in two forms: nonbullous and bullous. In nonbullous impetigo, smaller vesicles and pustules rupture and form a crust, while bullous impetigo is characterized by the presence of larger bullae that also rupture and become crusted sores.