What is acne?

Posted on : 09.08.2019

Acne is not a new ailment. It was described in ancient writings by the Egyptians who called it “Aku-t”, but it’s likely that humans have been battling spots and blemishes since prehistoric times.[1] The exact causes remain unclear, but one thing we know is that acne does not discriminate. It’s estimated that up to 80% of people are affected by acne at some point in their lives.[2]


Define acne

Acne comes in many forms, with different levels of severity, so let’s begin by defining what we mean by ‘acne’. The most common form is acne vulgaris, which is a horrible name that seems to imply something offensive, but the word vulgaris really just means ‘common’ in Latin. Other forms of acne can potentially be much more serious, so it’s always best to see your doctor for a diagnosis so you know what you’re dealing with. In this article when I say acne I’m referring to acne vulgaris.


A pore excuse

There’s more to acne than just pimples and blackheads, but to understand the types and causes we need to get acquainted with the landscape of acne-prone skin. Beauty bloggers love to talk about pores, but let’s get something straight, what we think of as ‘pores’ are actually hair follicles. You have about 5 million of them across your body, and each one is home to (usually) a single hair, most of which are so short and fine you barely notice them. If you drove down any one of these hair follicles, you would notice a turnoff a little way down leading to a cul-de-sac, otherwise known as a sebaceous gland. This gland’s job is to produce sebum, an oily substance that travels up the hair and out the follicle opening where it provides moisturisation and waterproofing to the skin and hair. It also carries dead skin cells out of the hair follicle and up to the surface, and this is where things can sometimes go awry.


The acne cycle

Acne involves the interplay of four distinct factors, on top of the genetic predisposition, which appears to be the main underlying cause.[2] It’s a combination of these factors that leads to blocked follicles, which present as those characteristic spots that we all know and hate.

  1. Hyperkeratinisation – When too many skin cells try to exit the hair follicle at once, it’s like when every vehicle tries to leave the carpark at once — gridlock.
  2. Excess sebum production
  3. Presence of particular strains of bacteria (Cutibacterium acnes)
  4. Inflammation

Sebum production is influenced by various hormones, which we all know are rampant during puberty — one reason puberty and acne often go hand in hand — but can also be triggered by stress and other factors.[2] C. acnes bacteria eat the fatty acids in sebum and release inflammatory mediators, which leads to hyperkeratinisation, more blocked follicles, further stress, and round and round it goes.


Spot the spot

Acne is usually classified as mild, moderate or severe, but there’s no consensus on what those really mean. Some sources base the definition on the number of spots while others go by the types (comedones, papules, nodules etc.). 

Comedones – A plugged hair follicle without inflammation. Includes blackheads and whiteheads. Blackheads occur when the follicle is open at the top. The dark colour comes from a build-up of melanin, the skin’s natural pigment, and not dirt as is commonly believed.[3]

Papules and Pustules – Papules are small, inflammatory lesions that do not contain pus, while pustules (unsurprisingly) do.[3]

Nodules – More commonly known as cystic acne, nodules are painful, inflammatory lesions that extend deeper into the skin[3]


As a rough guide, fewer than 30 lesions, mainly comedones, qualifies as mild acne. Once papules and pustules enter the scene, or the spot count is 30 – 125, you’re looking at moderate acne. Severe acne is defined as a large number of lesions (more than 125), with large nodules present.[2,4] Again, it’s best to see a doctor for a diagnosis because treatment and management options will differ.



  1. Tabasum H, Ahmad T, Rehman H, Anjum F. The historical panorama of acne vulgaris. J Pak Assoc Dermatol 2013;23(3).
  2. Acne Vulgaris: Practice Essentials, Background, Pathophysiology [Internet]. Medscape2019 [cited 2019 Jul 25];Available from:
  3. Layton AM. Disorders of the Sebaceous Glands. In: Burns T, Breathnach S, Cox N, Griffiths C, editors. Rook’s Textbook of Dermatology. Oxford, UK: Wiley-Blackwell; 2010. page 1–89.
  4. Oakley A. Acne | DermNet NZ [Internet]. [cited 2019 Jul 31];Available from:


Contributor Josh Townley

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