Follicular plugging

In a normal follicle, the keratinocytes are shed as single cells into the follicular channel and then excreted. It is not fully understood what stimulates the hyperkeratinisation in which the dead keratinocytes remain adherent in the follicular channel leading to blockage, which can be either partial or complete. However, initially these blockages lead to small virtually invisible changes which are the microcomedones. They may take up to 2–3 years before they proceed into more significant acne lesions. As the microcomedone gets bigger and the swelling increases behind the blockage, comedones develop. These are always the precursor lesions to acne.

Comedones can either be open or closed. Open comedones (otherwise known as blackheads) are where the blockage of the follicle is high up and contents of the follicle are pushed through the follicle opening, thus being exposed to the air. The black colour of blackheads is not caused by dirt, although there appears to be disagreement about its origins. Texts vary, with some saying it is due to the presence of melanin (Ashton and Leppard, 2005), others to the way that light is reflected of the tightly compacted horny cells (Leyden and McGinley, 1993) and yet others stating it is caused by the oxidising effect of the air on the contents of the comedone (O’Toole, 1997) (Figure 10.2). Closed comedones (otherwise known as whiteheads) do not have their contents exposed to the air as the blockage is further down the hair follicle. Blackheads and whiteheads are the non-inflammatory stage of acne (Figure 10.3). Acne can resolve spontaneously at this stage never progressing to the inflammatory form of the disease. The blockage within the follicle allows for a build up of sebum which becomes the ideal environment for P. acnes to proliferate.

Figure 10.2 Open comedones. (Source: Reprinted from Weller et al., 2008.)

Figure 10.3 Acne with comedones. (Source: Reprinted from Buxton and Morris-Jones, 2009.)