Acne: what it is, and how a dermatologist looks at it

Acne is an inflammatory condition of the pilosebaceous unit, the small structure that pairs a hair follicle with an oil gland. When that unit becomes blocked and inflamed, the visible result ranges from small blocked pores to deeper, tender lesions. It is common, it is treatable, and it is not caused by poor washing.

What is actually happening in the skin?

Every hair on the body sits in a follicle, and most follicles have an oil gland attached to them. Together they make up what dermatologists call the pilosebaceous unit, and acne is a condition of that unit rather than of the skin surface above it. The distinction sounds academic until you notice how much advice ignores it.

Several things happen together. The gland produces more sebum than usual, often under hormonal influence. The lining of the follicle sheds cells that stick rather than clearing, so the channel narrows. Bacteria that live harmlessly on everybody’s skin find the altered conditions inside a blocked follicle much more hospitable, and the immune system responds to what is going on there. That immune response is the redness and the tenderness.

None of it is visible while it is happening.

The order matters less than the fact that all of it takes place below the surface. Washing acts on the outside of the epidermis; the blockage is further down the follicle, out of reach. This is why scrubbing produces irritated skin rather than clearer skin, and why dermatologists tend to be unenthusiastic about vigorous cleansing routines.

Where the pilosebaceous units are densest is where acne appears, which is why the face, chest and upper back are the usual sites and the shins are not. Acne follows the anatomy rather than the habits of the person carrying it.

How would a dermatologist describe it?

Listen in a dermatology clinic and you will hear acne described by lesion type rather than by severity alone, and the vocabulary of acne is worth having, because it is the difference between saying it is bad at the moment and describing something a clinician can act on.

A comedone is a blocked follicle without much inflammation. Open comedones reach the surface and darken through oxidation, which is where the term blackhead comes from; the colour is not dirt. Closed comedones stay under a thin layer of skin and look like small pale bumps. Papules are small, raised, inflamed lesions, and pustules are the same thing with visible pus. Nodules sit deeper. They feel firm, they are usually tender, and they are the type most associated with lasting change to the skin.

Those five words cover most of what gets described.

Two further words come up constantly in acne. Post-inflammatory hyperpigmentation is the flat discolouration left behind after inflammation settles, and it is a pigment change rather than damage to the structure of the skin. Scarring means something different and more specific: an actual alteration in the skin’s architecture, which behaves differently over time. Hearing which of the two a clinician is describing tells you a great deal.

Distribution and pattern get described too, because acne on the jawline in an adult raises different questions from acne across the forehead in a teenager.

What usually happens at a consultation?

Expect the conversation to be longer than the examination. A dermatologist will want to know how long this has been going on, whether it fluctuates, what makes it better or worse, what has already been tried and for how long, and what else is going on medically. Questions about menstrual cycles, other medicines and family history are routine rather than intrusive.

The examination itself is usually straightforward: good light, sometimes magnification, looking at which lesion types are present and where. A clinician may look at your back and chest even if you came about your face, since the distribution is part of the picture.

Photographs are sometimes taken, with your agreement, because acne changes slowly and comparing two points in time is more informative than either alone. The question of what to do next is answered in that room, in the context of your history, and it is the part of the appointment this page has nothing useful to add to.

What is worth asking?

Ask which lesion types the clinician is seeing, and where. That answer shapes everything that follows, and it gives you a vocabulary for describing changes later without having to hold your phone up to a camera.

Ask how long the approach being discussed usually takes before anyone can judge whether it is working. Acne responds slowly, expectations tend to be optimistic, and the most common reason people conclude that something has not worked is that they assessed it too early.

Ask what the clinician would want to know about between now and any follow-up. Framed that way, you get a description of what to watch rather than general reassurance, which is far more useful when something changes on a Sunday evening.

If marks left behind are part of why you came, ask whether what is being seen is pigment change or textural change. They are different problems with different timescales, and conflating them is the single most common source of disappointment in this area.

What this page does not do

It does not tell you whether what is on your skin is acne; only someone examining you can say that. It does not recommend, compare or rank any treatment, and it gives no doses, schedules or product names, because those belong to a clinician who knows your history.

Last updated 2026-08-03. How this page was written.