Which of the following is affected during the development of a furuncle?

Furuncles (boils) usually sta in infected hair follicles, though some are caused by retained foreign bodies and other injuries. If the pilosebaceous apparatus becomes obstructed at the skin level, the development of a furuncle can be anticipated. Because the base of the hair follicle may lie in subcutaneous tissue, the infection can spread as cellulitis or it can form a subcutaneous abscess. Ref: Mundy L.M., Dohey G.M. (2010). Chapter 8. Inflammation, Infection, & Antimicrobial Therapy. In G.M. Dohey (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.