Final answer:
A boil, or furuncle, develops when the duct of a sebaceous gland becomes blocked, often leading to infection and inflammation.
Step-by-step explanation:
A "boil" or furuncle develops when B. The duct of a sebaceous gland becomes blocked. Furuncles are deeper infections characterized by the presence of pus and often caused by Staphylococcus bacteria. These boils are common in teenagers and young adults, particularly those engaging in contact sports, living in close quarters, or with weakened immune systems. Blocked oil glands cause inflammation, which can lead to a pimple or, when further infected, a boil. Proper hygiene and skin care are essential for preventing and managing furuncles.