What do antibiotics do for acne?

To understand why tetracycline antibiotics (note: not just any antibiotic) work in acne, we need to review acne's pathogenesis.

The problem all begins when our skin's pores get blocked. Contrary to popular belief, this has nothing to do with 'being dirty' - washing your face with soap and water won't help prevent acne. Rather, the pores get plugged with skin cells (keratinocytes), which fail to slough off properly in this condition. As you can see from the picture on the right, the skin 'pores' are where the hair follicles exit. Each one has its own sebaceous gland, which is the white ball sticking out to the side of each follicle. These glands produce sebum, an oily substance that lubricates the skin.

The plugged pores, together with sebum as a food source, provide a nice safe haven for the overgrowth of a normal skin commensal (the bacterium Priopionibacterium acnes) to take place within the structure. The body senses this proliferation of bacteria, and sends in its arsenal of neutrophils, which creates pus out of the whole mess. Furthermore, the follicle wall takes 'friendly fire' from the neutrophils' destructive enzymes, which can eventually lead to the structure bursting. The debris, now in the (deeper) dermis layer of the skin, only attracts more immune system attention, resulting in more inflammation. Thus, we progress from a blocked follicle to a pustule with inflammed surrounding skin.

Did that all make sense? One thing you can't fail to notice is that a certain bacterium - P. acnes - has a lot to answer for. And this is exactly why certain antibiotics can improve acne symptoms. With the troublesome bacterium out the way, the skin is not nearly so badly affected. (Of course, there are other treatments on offer as well.)