Acne
Acne explained — what it is, types of spots, causes and triggers. A clinical UK guide to acne vulgaris from Access Doctor.
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Acne UK: Types, Causes & Symptoms Explained
Key fact: Acne is the most common skin condition in the UK, affecting around 95% of people aged 11–30 to some degree. It is a disease of the hair follicle and sebaceous gland — not a result of poor hygiene — and it is highly treatable. This guide explains what acne is, the different types, and what causes it. For treatment options, see our acne treatment page.
Acne is a chronic inflammatory condition of the pilosebaceous unit — the structure made up of a hair follicle and its associated sebaceous (oil) gland. Although most strongly associated with adolescence, acne affects people of all ages, and adult acne is increasingly common. It is one of the most treatable skin conditions, but understanding what it is and what drives it is the first step to managing it effectively.
This page is a clinical overview of what acne is, the types of lesions it produces, and the factors that cause and trigger it. If you are looking for treatment, our acne treatment page covers the prescription and topical options available.
What Is Acne?
Acne (acne vulgaris) is a condition in which hair follicles become blocked with sebum (skin oil) and dead skin cells, creating an environment where the skin bacterium Cutibacterium acnes (formerly Propionibacterium acnes) can multiply and trigger inflammation. The result is the range of lesions associated with acne: blackheads, whiteheads, papules, pustules, and in more severe cases, nodules and cysts.
It most commonly affects the face, but also appears on the back, chest, and shoulders — areas with the highest density of sebaceous glands. Acne on those sites behaves differently and is slower to clear, which our guide to back, chest and body acne covers in detail. Acne is not caused by dirt or poor hygiene; in fact, over-washing and scrubbing can worsen it by irritating the skin and stripping its natural barrier.
How Acne Forms: The Four Key Factors
Four interacting processes drive the formation of acne. Most effective treatments target one or more of these.
| Process | What happens |
|---|---|
| Excess sebum | Androgens enlarge the sebaceous glands and increase oil production beyond what the pore can clear |
| Abnormal cell shedding | Skin cells lining the follicle shed too slowly and stickily, forming a plug (hyperkeratinisation) |
| Bacterial overgrowth | C. acnes multiplies in the oil-rich environment of the blocked follicle |
| Inflammation | The immune response to that overgrowth produces the redness, swelling and pain |
A blocked follicle (a comedone) is the starting point. When the blockage is open to the air, the trapped material oxidises and darkens, forming a blackhead. When closed over by skin, it forms a whitehead. If bacteria multiply and inflammation develops, the lesion becomes a red papule or a pus-filled pustule. Deeper, more severe inflammation produces nodules and cysts.
Types of Acne Lesions
| Lesion type | Description | Inflammatory? |
|---|---|---|
| Blackheads (open comedones) | Blocked follicles open to the surface; dark due to oxidation, not dirt | No |
| Whiteheads (closed comedones) | Blocked follicles closed over by skin; small flesh-coloured bumps | No |
| Papules | Small, red, raised, tender bumps caused by inflammation | Yes |
| Pustules | Inflamed lesions containing visible pus at the tip | Yes |
| Nodules | Large, hard, painful lumps deep under the skin | Yes (severe) |
| Cysts | Large, pus-filled lesions deep in the skin; highest scarring risk | Yes (severe) |
Most people have a mix of lesion types. The balance — whether acne is predominantly comedonal (blackheads and whiteheads) or inflammatory (papules, pustules, nodules) — influences which treatments are most appropriate.
Not everything that looks like acne is acne. Itchy, uniform bumps, spots clustered around the mouth, or painful lumps in the armpits and groin all point elsewhere — see what else looks like acne.
Grades of Acne: Mild, Moderate and Severe
- Mild acne — mostly blackheads and whiteheads, with a few papules and pustules. Usually managed with topical treatments.
- Moderate acne — more widespread papules and pustules, often with some early nodules. Frequently needs a combination of topical and oral treatment.
- Severe acne — widespread inflammatory lesions, nodules and cysts, often with scarring. Requires prompt medical treatment and sometimes specialist referral.
Why grade matters: Severe nodulocystic acne carries the highest risk of permanent scarring. It should be treated early and assertively rather than waited out. If you have deep, painful lumps or cysts, seek treatment promptly rather than relying on over-the-counter products.
Severe acne that has not responded to standard treatment, or that is scarring, is the point at which dermatology referral for isotretinoin becomes the appropriate route. It is a hospital-only medicine in the UK and cannot be prescribed online.
What Causes Acne?
Acne is driven primarily by hormonal and genetic factors, not by lifestyle alone. The main underlying causes are:
Hormones
Androgens enlarge sebaceous glands and increase oil production — which is why acne peaks in puberty and fluctuates across the menstrual cycle.
Genetics
A strong family history makes acne both more likely and potentially more severe, and is a reason to treat earlier rather than wait.
Bacteria
C. acnes overgrowth within blocked follicles is what converts a comedone into an inflamed, painful lesion.
Immune response
How strongly the immune system reacts to that overgrowth varies between people, and largely determines how inflamed acne becomes.
In women, acne is often linked to hormonal fluctuations across the menstrual cycle, and can be a feature of polycystic ovary syndrome (PCOS), particularly when accompanied by irregular periods and excess hair growth. Acne that begins or persists in adulthood behaves differently from teenage acne — deeper, lower on the face, and often cyclical — and is covered in adult and hormonal acne.
Common Acne Triggers
Triggers do not cause acne on their own, but they can worsen existing acne in susceptible people:
- Hormonal changes — puberty, menstrual cycle, pregnancy, PCOS, and stopping the combined pill
- Certain medications — some steroids, lithium, and certain hormonal contraceptives
- Comedogenic skincare and cosmetics — heavy, pore-blocking products
- Friction and pressure — tight helmet straps, face masks, and phone screens against the skin
- Picking and squeezing — worsens inflammation and significantly increases scarring risk
- Diet — evidence is limited, but high-glycaemic diets and, in some studies, skimmed milk may contribute modestly in some people
On hygiene: Acne is not caused by dirt. Washing more than twice a day, or scrubbing hard, irritates the skin and can make acne worse. A gentle cleanser twice daily is all that is needed.
Acne Myths and Misconceptions
- Myth: Acne is caused by poor hygiene. Acne is driven by hormones, genetics, and follicle biology — not dirt. Over-washing makes it worse.
- Myth: Chocolate and greasy food cause acne. The dietary link is weak and inconsistent; no single food causes acne for most people.
- Myth: Sunbathing clears acne. Sun may temporarily mask redness but damages skin and can worsen acne and pigmentation long-term.
- Myth: You should let acne run its course. Untreated inflammatory acne risks permanent scarring; early treatment protects the skin.
- Myth: Popping spots helps them heal. Squeezing pushes inflammation deeper, delays healing, and increases scarring.
- Myth: Once it clears, you can stop everything. Acne usually returns within months if treatment stops entirely — see acne maintenance and relapse.
Acne Scarring and Why Early Treatment Matters
One of the most important reasons to treat acne — rather than wait for it to clear on its own — is to prevent scarring. Inflammatory acne, particularly nodules and cysts, can damage the deeper layers of skin and leave permanent textural scars (such as ice-pick or rolling scars) or persistent dark marks (post-inflammatory hyperpigmentation).
Scarring is far easier to prevent than to treat. This is why dermatology guidance emphasises treating moderate-to-severe acne early and effectively, and avoiding picking or squeezing lesions. If your acne is leaving marks or scars, it is a clear signal to seek treatment rather than continue waiting.
Most of what people call scarring is in fact flat pigmentation, which fades on its own. Telling the two apart takes a second and changes what you should do about it — see acne scars and marks.
When to Seek Medical Help
Most acne can be managed effectively. Seek treatment or medical advice if:
- Over-the-counter products have not improved your acne after 2–3 months
- You have moderate-to-severe acne with papules, pustules, nodules or cysts
- Your acne is leaving scars or persistent dark marks
- Acne is affecting your confidence, mood, or quality of life
- You are a woman with acne alongside irregular periods or excess hair growth (possible PCOS)
- You develop sudden severe acne, especially with other symptoms, which warrants assessment
- Spots are itchy, all the same size, or got worse on antibiotics — which suggests it may not be acne
Acne and mental health: Acne can have a significant psychological impact. If acne is causing low mood, anxiety, or distress, this is a valid reason to seek help — both for the skin and for your wellbeing. Speak to your GP or pharmacist; effective treatment is available.
In children and teenagers the case for treating early is the same, and the practical obstacles are different — our guide to acne in teenagers is written for parents.
Looking for Acne Treatment?
This page explains what acne is and what causes it. For prescription and topical treatment options — assessed and prescribed by GPhC-registered pharmacist independent prescribers via a short online consultation — visit our acne treatment page. No GP appointment needed.
View Acne Treatment Options →All Acne Guides
Eleven guides cover acne in depth — from telling a mark from a scar, to what to do when treatment stops working.
Frequently Asked Questions about Acne
Is acne caused by poor hygiene?
No. Acne is caused by excess oil production driven by hormones, blocked follicles, bacterial overgrowth, and inflammation — not by dirt. Washing too often or scrubbing can irritate the skin and make acne worse. A gentle cleanser twice a day is sufficient.
Why do adults get acne?
Adult acne is increasingly common, particularly in women aged 20-40. It is often driven by hormonal fluctuations including the menstrual cycle and PCOS, stress, certain medications, and genetics. Adult acne tends to affect the lower face, jawline, and neck.
What is the difference between a blackhead and a whitehead?
Both are blocked follicles (comedones). A blackhead is open to the surface so trapped material oxidises and darkens — the dark colour is oxidation, not dirt. A whitehead is closed over by skin, appearing as a small flesh-coloured bump. Neither is inflammatory.
Does diet cause acne?
The evidence linking diet to acne is limited and inconsistent. Some studies suggest high-glycaemic-index diets and in some cases skimmed milk may modestly worsen acne in certain people, but no single food causes acne for most. Hormones and genetics are far more important.
Will acne go away on its own?
Acne often improves with age as hormones stabilise, but this can take years, and inflammatory acne can leave permanent scarring in the meantime. Because scarring is much easier to prevent than treat, it is usually better to treat moderate-to-severe acne early.
Can squeezing spots make acne worse?
Yes. Squeezing or picking pushes inflammation deeper, delays healing, spreads bacteria, and significantly increases the risk of permanent scarring and dark marks. It is one of the most common avoidable causes of acne scarring.
Is acne linked to PCOS?
It can be. Acne is one feature of polycystic ovary syndrome (PCOS), particularly alongside irregular periods, excess hair growth, and weight difficulties. Persistent adult acne in women that does not respond to standard treatment may warrant assessment for PCOS.
Why does my acne come back whenever I stop treatment?
Because acne treatment suppresses the process causing acne rather than curing it. The hormonal drivers behind excess oil and blocked follicles do not change because the skin has cleared, so stopping allows the process to resume. Skin often stays clear for a few weeks on momentum, which is long enough to conclude the acne has gone. A lighter ongoing maintenance treatment is what keeps most people clear.
References
- National Institute for Health and Care Excellence. Acne vulgaris: management (NG198). nice.org.uk/guidance/ng198
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Acne vulgaris. cks.nice.org.uk
- Layton AM, et al. British Association of Dermatologists’ guidelines for the management of acne vulgaris. Br J Dermatol. 2021;185(6):1012–1030.
- NHS. Acne. nhs.uk/conditions/acne
- DermNet. Acne and acneiform eruptions. dermnetnz.org
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Several acne treatments, including oral retinoids and the tetracycline antibiotics, must not be used in pregnancy or when there is any chance of becoming pregnant. Acne treatment takes weeks to months to work and a short-lived worsening at the start is common. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.
