If you are trying to work out whether your acne is bacterial or hormonal, here is the honest starting point: these are not two separate diseases. Acne vulgaris is one condition driven by several mechanisms at once, and the bacteria involved live on almost everyone’s skin, including people who never break out. What differs between individuals is which mechanism dominates, and that is genuinely worth identifying, because it changes what treatment will work.
- Cutibacterium acnes is a normal skin commensal. It is present in similar quantities on people with and without acne.
- What differs is the strain population, not the bacterial load, so acne is not an infection you catch or cure with antibiotics.
- Androgens drive sebum production in all acne, teenage and adult. Hormones are part of the picture for everyone.
- Pattern still helps. In 1,867 adult women, chin involvement was 91.4% and nose involvement only 21.8%.
- But most people are not neatly one or the other: the commonest pattern was acne in two facial areas at once.
- NICE is explicit that antibiotics should never be used alone to treat acne.
- Resistance in C. acnes to erythromycin rose from 10% in 2008 to 44% in 2024.
- For persistent acne in adult women, spironolactone gave 81.9% self reported improvement at 24 weeks against 63.3% on placebo.
abundance of C. acnes on the skin of people with and without acne
Fitz-Gibbon et al., JID 2013
of adult women in a population study had acne on the face or back
Acta Derm Venereol, 2025
erythromycin resistance in C. acnes by 2024, up from 10% in 2008
Front Microbiol, 2025
reported improvement on spironolactone at 24 weeks, against 63.3% on placebo
SAFA trial, BMJ 2023
All figures are drawn from the peer reviewed studies and national guidance listed at the end of this article. They describe published study populations and are not a prediction of any individual outcome.
The short answer
Bacterial and hormonal acne are not two diagnoses. They are two ways of describing which part of the same process is doing most of the damage in your particular case. Acne vulgaris develops through four mechanisms that all operate together:
- Androgens increase sebum production. This is the hormonal part, and it is present in essentially all acne, not just the kind people label hormonal.
- The follicle lining thickens and blocks the pore. Dead cells that should shed instead stick together and plug the opening.
- Cutibacterium acnes proliferates inside the blocked follicle. This is the bacterial part. The organism was already there before the acne started.
- The immune system reacts. Inflammation is what turns a blocked pore into a red, sore spot, and it is what causes scarring.
What the evidence says about the bacteria
The single most useful thing to understand is that Cutibacterium acnes is not an invader. It is a normal resident of human skin, and people without acne carry roughly as much of it as people with acne.
Fitz-Gibbon and colleagues at UCLA sampled the pilosebaceous units on the noses of 49 acne patients and 52 healthy individuals and sequenced what they found. The result reframed how dermatology thinks about the bacterial component.
Metagenomic analysis demonstrated that although the relative abundances of P. acnes were similar, the strain population structures were significantly different in the two cohorts. Certain strains were highly associated with acne, and other strains were enriched in healthy skin.
Fitz-Gibbon S, Tomida S, Chiu BH, et al. “Propionibacterium acnes strain populations in the human skin microbiome associated with acne.” Journal of Investigative Dermatology, 2013. 49 acne patients and 52 healthy individuals. The organism has since been renamed Cutibacterium acnes.
Two practical conclusions follow from this. First, acne is not an infection, so it is not something you can wash off or sterilise away, and the instinct to scrub harder makes it worse rather than better. Second, killing bacteria indiscriminately is a blunt approach to a problem that turns on which strains are present, which is one reason antibiotic monotherapy performs so poorly over time.
What the evidence says about hormones
Androgens such as testosterone stimulate the sebaceous glands. That mechanism operates in every case of acne, which is why calling only some acne hormonal is misleading. What people usually mean by hormonal acne is acne whose timing or distribution follows hormonal fluctuation, most often in adult women.
That group is large. A cross sectional population study of 1,867 women with a mean age of 35.3 years found that 31.3% had acne on the face or back, leading the authors to describe female adult acne as a common disease affecting about one third of women.
- Menstrual cycle
- Predictable premenstrual flares are the classic pattern. Tracking breakouts against your cycle for two or three months is the simplest diagnostic test available, and it costs nothing.
- PCOS
- Raised androgens produce persistent acne alongside irregular periods and excess hair growth. NICE advises considering referral to a specialist where acne occurs with additional features of hyperandrogenism.
- Pregnancy and postpartum
- Acne can improve or worsen. Treatment options narrow considerably during pregnancy and breastfeeding, so this always needs medical input rather than self treatment.
- Perimenopause
- Falling oestrogen shifts the androgen to oestrogen balance, which can trigger acne in women who had clear skin for decades.
- Sudden adult onset
- Acne that appears abruptly in an adult, particularly with other hormonal symptoms, warrants assessment rather than a new cleanser. It is one of the few genuine red flags in this area.
The pattern that does help you tell them apart
Distribution and timing are the two features that carry real information. Use them as a pointer rather than a verdict.
| Feature | Points towards inflammatory or bacterial dominance | Points towards hormonal dominance |
|---|---|---|
| Where it appears | Forehead, nose and upper cheeks, where sebaceous glands are densest | Chin, jawline and neck, the lower third of the face |
| What the spots look like | A mix of blackheads, whiteheads, papules and pustules, often surface level | Deeper, tender nodules and cysts that may never come to a head |
| Timing | Fairly constant, without a clear rhythm | Cyclical, often flaring in the week before a period |
| Age | Most common in teens and early twenties, affecting all genders similarly | Frequently persists or begins in the twenties, thirties and forties, mainly in women |
| Response to topicals | Usually responds to a properly used topical regimen | Often stubborn to topicals alone, and improves when the hormonal driver is addressed |
| Other symptoms | None beyond the skin | May come with irregular periods, excess hair growth or hair thinning |
The caveat that most articles leave out
The same population study measured where acne actually sits on adult women’s faces, and the results support the lower face pattern without supporting a neat split.
| Facial area | Proportion of adult women with acne there |
|---|---|
| Chin | 91.4% |
| Cheeks | 69.2% |
| Forehead | 33.5% |
| Nose | 21.8% |
The chin dominates, exactly as the hormonal pattern predicts. But cheek involvement at 69.2% is high, and the most common presentation overall was acne affecting two facial areas at once, in 40.2% of cases. In other words, most people do not fit cleanly into one column of the table above, and a plan built on the assumption that they do will often disappoint.
Treatment: what works, and for which mechanism
Nearly every effective acne treatment works on more than one mechanism, which is another reason the bacterial versus hormonal split breaks down in practice. A retinoid unblocks the follicle and reduces inflammation. Benzoyl peroxide reduces bacteria and is mildly comedolytic. Combination therapy is the norm precisely because single mechanism treatment underperforms.
The foundation
- Topical retinoidsAdapalene, tretinoin. Normalise how the follicle lining sheds. The single most useful class in acne.
- Benzoyl peroxideReduces C. acnes without driving resistance, which is why it is paired with antibiotics rather than replaced by them.
- Azelaic acidAntibacterial and anti-inflammatory, well tolerated, and useful in pregnancy where options are limited.
- Salicylic acidExfoliates inside the pore. Helpful for comedonal patterns.
Addresses the cause
- SpironolactoneAnti-androgen. Now supported by a large UK randomised trial in adult women.
- Combined oral contraceptivesNICE lists co-cyprindiol or an alternative combined pill as an add-on where first-line treatment is not enough.
- Investigation for PCOSWhere there are additional signs of hyperandrogenism, the acne is a symptom rather than the problem.
- IsotretinoinFor severe or scarring acne that has not responded. Specialist supervised.
Adjuncts
- Chemical peelsSalicylic or glycolic peels clear surface blockage and improve texture.
- Intralesional steroidSettles a single painful cyst quickly. Useful before an event, not a treatment plan.
- Scar treatmentConsidered once active acne is controlled, not alongside it. See acne scar treatment.
- Prescription reviewWhere over the counter products have failed, prescription acne treatment opens the options above.
The antibiotic problem
If your acne has been labelled bacterial and you have been given antibiotics on their own, that is contrary to current UK guidance. The National Institute for Health and Care Excellence is unambiguous about it.
Do not use the following to treat acne: monotherapy with a topical antibiotic, monotherapy with an oral antibiotic, a combination of a topical antibiotic and an oral antibiotic.
NICE guideline NG198, Acne vulgaris: management, recommendation 1.5.11. See the full NICE recommendations on acne management.
The same guideline advises continuing any antibiotic containing regimen beyond six months only in exceptional circumstances, reviewing every three months, and stopping the antibiotic as soon as possible. The reason is visible in the resistance data.
| Antibiotic | Pooled resistance in C. acnes | What it means |
|---|---|---|
| Erythromycin | 29.2% | Rose from 10% in 2008 to 44% in 2024. Increasingly unreliable. |
| Clindamycin | 22.4% | Also rising over time. Should always be paired with benzoyl peroxide. |
| Doxycycline | 2.4% | Resistance remains low, which is why tetracyclines stay first choice among oral antibiotics. |
| Tetracycline | 1.3% | Lowest reported resistance in the pooled analysis. |
These figures come from a 2025 systematic review and meta-analysis of 23 studies covering 2,046 C. acnes isolates. Pairing an antibiotic with benzoyl peroxide is the standard way to reduce resistance development, and it is why you will rarely be prescribed one without the other.
Hormonal treatment: what the trial evidence shows
For persistent acne in adult women, spironolactone now has proper randomised evidence behind it from a UK trial. The SAFA study was a pragmatic, multicentre, phase 3, double blind randomised controlled trial run in England and Wales and published in the BMJ in 2023.
| Outcome | Spironolactone | Placebo |
|---|---|---|
| Self reported improvement at 12 weeks | 72.2% | 67.9% |
| Self reported improvement at 24 weeks | 81.9% | 63.3% |
| Treatment success at 12 weeks (investigator assessed) | 31 of 201 | 9 of 209 |
Two things stand out. The difference at 12 weeks was small and not statistically significant, while by 24 weeks it clearly was, with an odds ratio of 2.72. Hormonal treatment is slow, and judging it at three months underestimates it. The trial also found the drug well tolerated at 50 mg and 100 mg, with headache and lightheadedness the main differences from placebo.
When to see a dermatologist
- Over the counter treatment has not worked after a proper 12-week trial
- You have deep, painful nodules or cysts
- Spots are leaving scars or dark marks behind
- Acne has appeared suddenly in adulthood
- Breakouts come with irregular periods, excess hair growth or hair thinning
- You have been on an antibiotic for acne for more than six months
- Your skin is affecting your mood, confidence or social life
That last point is not a soft criterion. Acne severity on examination correlates poorly with how much it affects someone’s life, and distress is a legitimate reason to seek treatment regardless of how mild the acne looks to anyone else.
Do and avoid
Do
- Track breakouts against your cycle for two or three months
- Photograph your skin weekly in the same light
- Give any treatment a full 12 weeks before judging it
- Use benzoyl peroxide alongside any antibiotic
- Keep using a non-comedogenic moisturiser and daily SPF
- Ask about hormonal options if topicals have failed
Avoid
- Treating acne as a hygiene problem and over cleansing
- Taking an antibiotic on its own for acne
- Staying on an antibiotic for more than six months
- Switching products every few weeks
- Picking or squeezing, which drives scarring
- Assuming jawline spots must be hormonal without checking the pattern
Frequently asked questions
How can I tell if my acne is hormonal or bacterial?
Look at distribution and timing rather than appearance alone. Acne concentrated on the chin, jawline and neck that flares in the week before a period points towards a hormonal driver. Acne spread across the forehead, nose and upper cheeks with a mix of blackheads, whiteheads and pustules, and no clear rhythm, points towards inflammatory or bacterial dominance. Bear in mind that in a study of 1,867 adult women, the commonest presentation was acne in two facial areas at once, so most people are a mixture.
Is acne actually an infection?
No. Cutibacterium acnes is a normal skin commensal, and a metagenomic study of 49 acne patients and 52 healthy people found similar relative abundances of the organism in both groups. What differed was which strains were present. Acne is an inflammatory condition of the hair follicle, not something you catch, and it cannot be washed away.
Why did antibiotics stop working for my acne?
Resistance is a large part of the answer. In a 2025 meta-analysis of 23 studies and 2,046 isolates, erythromycin resistance in C. acnes had risen from 10% in 2008 to 44% in 2024, with clindamycin resistance also increasing. This is why NICE advises against using antibiotics on their own for acne, recommends pairing them with other agents, and advises continuing them beyond six months only in exceptional circumstances.
Can I have both bacterial and hormonal acne at the same time?
Effectively everyone does, because both mechanisms are part of how acne forms. Androgens increase sebum, the follicle blocks, bacteria proliferate inside it and the immune system reacts. The useful question is which of these is dominant in your case, because that determines whether topical treatment alone is likely to be enough.
Does hormonal acne always mean I have PCOS?
No. Most women with cyclical acne have normal hormone levels and simply have sebaceous glands that are more sensitive to normal androgen fluctuation. PCOS becomes a real consideration when acne appears alongside irregular periods, excess hair growth or difficulty conceiving, and NICE advises considering specialist referral where acne occurs with additional features of hyperandrogenism.
Does spironolactone work for adult acne?
Yes, with proper trial evidence behind it. In the SAFA randomised controlled trial run in England and Wales, 81.9% of women taking spironolactone reported improvement at 24 weeks against 63.3% on placebo, a statistically significant difference. The gap at 12 weeks was much smaller, which is a useful reminder that hormonal treatment takes time to show its full effect.
How long should I give a treatment before giving up on it?
Twelve weeks. NICE recommends offering a 12-week course of a first-line treatment and reviewing at that point. Abandoning a treatment at three or four weeks is one of the commonest reasons people conclude that nothing works, when in reality nothing has been given long enough to work.
Will changing my diet clear hormonal acne?
Diet is not a treatment, though it can be a modifier. Some people find that high glycaemic foods and dairy worsen their breakouts, and a food and skin diary is a reasonable way to test that for yourself. It is not a substitute for treatment where acne is moderate, painful or scarring.
Does acne get better on its own with age?
Often, but not reliably. Acne affects around 85% of people aged 12 to 24, and most see it settle. In adult women it is common enough that a population study found 31.3% affected, with a mean age of 35. Waiting it out is a poor strategy if the acne is inflammatory, since the scarring it causes is far harder to treat than the acne itself.
Sources & references
- Fitz-Gibbon S, Tomida S, Chiu BH, et al. “Propionibacterium acnes strain populations in the human skin microbiome associated with acne.” Journal of Investigative Dermatology, 2013. 49 acne patients and 52 healthy individuals; similar relative abundance of the organism but significantly different strain population structures.
- NICE guideline NG198, “Acne vulgaris: management”, nice.org.uk. Recommendation 1.5.1 on 12-week first-line courses, 1.5.11 on not using antibiotic monotherapy, 1.5.13 on the six month limit, and 1.5.32 on referral where acne occurs with features of hyperandrogenism.
- Zhu C, Wei B, Li Y, Wang C. “Antibiotic resistance rates in Cutibacterium acnes isolated from patients with acne vulgaris: a systematic review and meta-analysis.” Frontiers in Microbiology, 2025;16:1565111. 23 studies, 2,046 isolates. Erythromycin 29.20%, clindamycin 22.38%, doxycycline 2.44%, tetracycline 1.31%.
- Telkkälä S, Jokelainen J, Piltonen T, Huilaja L, Sinikumpu SP. “The Prevalence and Characteristics of Adult Female Acne: A Cross-sectional Population-based Study.” Acta Dermato-Venereologica, 2025. 1,867 women, mean age 35.3 years; 31.3% prevalence; chin 91.4%, cheeks 69.2%, forehead 33.5%, nose 21.8%.
- Santer M, Lawrence M, Renz S, et al. “Effectiveness of spironolactone for women with acne vulgaris (SAFA) in England and Wales: pragmatic, multicentre, phase 3, double blind, randomised controlled trial.” BMJ, 2023.
This article is general information and does not replace individual medical advice. Figures quoted are from published studies and national guidance and are not a prediction of your own outcome. If your acne is painful, scarring or not responding to treatment, arrange an assessment.
Not sure what is driving your breakouts?
Book a consultation with Dr Simon Zokaie at our Harley Street clinic for a proper assessment of which mechanism is dominant in your skin, and a treatment plan built around it rather than around a label.
