Dermatitis is the inflammation of the skin, and folliculitis is the inflammation of the hair follicles. It often results from an infectious disease when opportunistic bacteria that normally live in the skin start infecting the insides of the hair follicle. After colonizing the area, an inflammatory reaction takes place as the body tries to defend itself. Thus, you will see reddened spots in the skin, and may even find acne-like lesions filled with pus. If you look closely, you will realize these spots have hairs right in the middle.