She felt much better as soon as we drained the cyst…
I put “infected” in quotes, because technically this is not an infection: When an epidermoid cyst ruptures, it creates a vigorous foreign body inflammatory response – this skin becomes warm, tender, painful, and swells, simulating an abscess. Incision and Drainage (I & D), will confirm the diagnosis of inflamed cyst, when the cheesy material is evacuated, and this often leads to rapid resolution of symptoms. Here you can see that the internal contents of the cyst have broken down and liquefied, and it’s impossible to define the wall of the cyst. These episodes are often misdiagnosed as “infection” of the cyst, but cultures are usually negative and antibiotic treatments is not required. I did a bacterial culture of this cyst and it proved to be “sterile”, that is, there was no bacterial growth in the culture.
All this being said, we often prescribe antibiotics- it’s hard not to when you see something so red and inflamed and painful.. it seems almost cruel not to! Also, we as dermatologists, will just call the cyst infected, or call it an abscess. It’s more difficult to explain to patients why we would not call an area that looks angry and red and is painful non-infected. However, I felt I needed to clarify all of this in detail here, for medical education purposes!