PCOS and Acne: Why It Happens and What Helps

✓ This content has been medically reviewed by an obstetrician and gynaecologist
Written & medically reviewed by: Op. Dr. Ayşet Jane Özcan, Obstetrics & Gynaecology Specialist
Istanbul Faculty of Medicine · Medical Park Bahçelievler · TJOD and TSRM member
Last updated: 24 October 2026 · Last medical review: 24 October 2026

Acne that sits along the jawline and chin, flares in the week before a period and shrugs off every spot cream in the bathroom cupboard is one of the commonest reasons women with polycystic ovary syndrome come to see me. PCOS affects somewhere around one in ten women of reproductive age, and acne is one of its three classic skin signs, alongside unwanted hair growth and thinning of the scalp hair. It is not a cosmetic footnote to the condition. For many women it is the symptom that affects daily life most, and it is often the one that gets the least structured attention.

The good news is that PCOS acne is understandable and treatable, provided the plan addresses the skin itself and, where needed, the hormonal driver behind it, and provided it is given enough time. Below I explain why PCOS causes acne, where it typically appears, how it differs from ordinary acne, what the treatment options actually are and how they are chosen, how long each one realistically takes to show a change, what diet and lifestyle can and cannot do, and when it is worth involving a dermatologist alongside your gynaecologist. This is general information, not a personal treatment plan: drug choice and dosing must be decided face to face by a doctor who knows your history.

Why PCOS Causes Acne: Androgens and Insulin Resistance

PCOS acne happens because androgens act on the oil glands of the skin, and in many women that androgen effect is amplified by insulin resistance. Both parts matter, because treatment works best when it addresses both.

Every sebaceous (oil) gland in the skin carries androgen receptors. When androgen activity rises, three things happen in the pore at once. The gland produces more sebum and the composition of that sebum changes. The cells lining the pore become stickier and shed abnormally, so the opening plugs. And the plugged, lipid-rich pore becomes a comfortable home for Cutibacterium acnes, the skin bacterium that lives harmlessly in everyone. The immune response to all of this is what you actually see and feel: a red, deep, tender lump rather than a simple blackhead.

In PCOS the androgen signal usually comes from the ovaries. The theca cells of the ovary, under a relatively high luteinising hormone drive, produce more testosterone and androstenedione than usual. In a proportion of women the adrenal glands contribute as well, which shows up as a raised DHEAS on blood tests. These are not male hormones that have appeared from nowhere; every woman makes androgens, and in PCOS the balance is simply shifted.

Where insulin comes in

Insulin resistance is common in PCOS, at every body size. When the tissues respond poorly to insulin, the pancreas compensates by producing more of it, and persistently high insulin does two unhelpful things. It stimulates the ovarian theca cells to make still more androgen, and it suppresses the liver's production of sex hormone binding globulin (SHBG), the protein that keeps testosterone bound and inactive in the bloodstream. Less SHBG means a higher free, active testosterone fraction even when the total level looks unremarkable. High insulin also raises insulin-like growth factor 1, which stimulates oil gland and skin cells directly. This is the mechanism behind one of the questions I am asked most often: why acne, irregular periods and difficulty with weight so frequently travel together.

One more point that saves a lot of frustration. Blood androgen levels and skin severity correlate loosely at best, because how strongly the skin responds depends on local enzyme activity (5-alpha-reductase, which converts testosterone into the more potent dihydrotestosterone inside the follicle) and on receptor sensitivity. A normal testosterone result does not mean your acne is not hormonally driven. If the pattern fits, the pattern counts. The same logic applies to the other early features of the condition, which I cover in more detail in what the first signs of PCOS look like.

Where PCOS Acne Typically Appears: Jawline, Chin, Neck, Chest and Back

Androgen-driven acne favours the lower third of the face, meaning the jawline, chin, the skin around the mouth and the upper neck, and often the chest, upper back and shoulders. Dermatologists sometimes call this the U-zone distribution, in contrast to the T-zone pattern over the forehead and central face that is typical of adolescent acne.

The lesions themselves also behave differently from teenage spots. They tend to be:

• Fewer in number but deeper, firmer and genuinely tender to touch
• Slow, so that a single lesion may take two to three weeks to come up and settle
• Short on visible whiteheads and blackheads, with more inflammatory papules, nodules and occasional cysts
• Prone to leaving flat brown or purple marks (post-inflammatory hyperpigmentation), which are more persistent and more noticeable on medium and deeper skin tones
• Repetitive, returning to the same few spots on the jaw or chin again and again

Timing is the other giveaway. Many women notice a reliable flare in the second half of the cycle, in the days before a period is due, when the hormonal environment of the skin shifts; the exact mechanism behind that premenstrual worsening is not fully established, but the observation itself is consistent enough to be clinically useful. If periods are infrequent, the pattern is less obvious but often worse overall, because long stretches without ovulation mean continuous, uninterrupted androgen exposure rather than the rise and fall of a normal cycle. Cycle length and skin behaviour are linked, which is why I always ask about both; the common reasons behind unpredictable cycles are set out in irregular periods: causes and when to worry.

Truncal involvement deserves a specific mention, because it is under-reported. Patients frequently describe facial acne and only mention chest and back lesions when asked directly. It matters, because acne on the trunk is harder to treat with creams alone, is more likely to scar, and often shifts the decision towards systemic treatment.

How PCOS Acne Differs From Ordinary Acne

Biologically it is the same disease process, but the pattern, the timing and the company it keeps are different, and those differences change the treatment plan. The features that point towards a hormonal driver rather than straightforward acne vulgaris are:

• Age and course. It starts in the twenties or thirties, or it never stopped after adolescence, rather than fading in the late teens.
• Distribution. Lower face and jawline dominance, often with the neck and trunk involved.
• Lesion type. Deep, tender, nodular lesions outnumber blackheads and whiteheads.
• Cyclicity. A predictable premenstrual flare, or a worsening during long gaps between periods.
• Treatment behaviour. It improves partially on topical treatment or a course of oral antibiotics and then relapses quickly once the course ends.
• Associated signs. Coarse hair on the chin, upper lip, chest or lower abdomen; thinning at the crown or a widening parting; persistently oily skin and scalp; irregular or absent periods; difficulty conceiving; velvety dark thickening of the skin in the armpits or neck folds (acanthosis nigricans), which suggests insulin resistance.

It is equally important to say what PCOS acne is not. Several conditions are routinely mistaken for it. Papulopustular rosacea affects the central face with flushing and visible vessels and produces no blackheads. Perioral dermatitis forms small bumps around the mouth and nostrils, classically after a topical steroid has been used on the face, and worsens if steroids are continued. Folliculitis produces uniform, often itchy pustules centred on hair follicles, typically after shaving, waxing or occlusion from sports clothing. Keratosis pilaris on the upper arms and cheeks is not acne at all.

Medicines and supplements can also produce acne or acne-like eruptions that have nothing to do with PCOS: oral corticosteroids, anabolic steroids and testosterone preparations, lithium, some anti-epileptics, certain targeted cancer drugs, and high-dose vitamin B supplements, particularly B12 and biotin. If your skin changed abruptly after starting something new, bring the box to the appointment.

What Happens at the Assessment and Which Tests Matter

PCOS is a clinical diagnosis supported by tests, not a diagnosis made by a blood result alone. The assessment has three jobs: confirm whether androgen excess is present, exclude the conditions that imitate PCOS, and check the metabolic picture that influences both the skin and long-term health.

The history covers when the acne began, how it has responded to previous treatments including any past isotretinoin course, cycle length and regularity, hair growth and hair loss, weight changes, current medicines and contraception, pregnancy plans, and the effect all of it is having on mood and daily life. The examination records the type and severity of lesions, scarring, truncal involvement, the pattern and extent of excess hair growth, scalp hair density, and signs of insulin resistance.

Blood tests commonly include total testosterone with SHBG, so that the free androgen fraction can be estimated, plus DHEAS, 17-hydroxyprogesterone to exclude non-classic congenital adrenal hyperplasia, prolactin and thyroid function. Ideally these are taken in the early part of the cycle, and they are not interpretable while you are taking a combined contraceptive pill, because the pill suppresses ovarian androgen production and raises SHBG. If androgen results genuinely need to be assessed, the pill usually has to be stopped for around three months first, which is a trade-off worth discussing before anyone stops anything.

A pelvic ultrasound may be used to look at ovarian morphology, and in some settings anti-Mullerian hormone is used as an alternative marker. Diagnosis rests on having two of three features, namely infrequent or absent ovulation, clinical or biochemical androgen excess, and polycystic ovarian morphology, once the mimics have been excluded. In adolescents, ultrasound is not used for diagnosis, because multifollicular ovaries are normal in the years after menarche. Metabolic screening with a fasting glucose or HbA1c, along with a lipid profile, is part of routine PCOS care rather than an optional extra.

Features that need prompt assessment

• Acne and excess hair growth that appear suddenly and worsen over weeks to months
• Deepening of the voice, hair loss at the temples, increased muscle bulk or clitoral enlargement
• A markedly raised testosterone level on testing
• Milky nipple discharge, severe headaches or visual change
• Easy bruising, purple abdominal stretch marks, muscle weakness and rapid central weight gain
• Painful interconnected nodules in the armpits, groin or under the breasts, which suggest hidradenitis suppurativa rather than acne

These point towards an androgen-secreting tumour, a prolactin-producing pituitary adenoma, Cushing's syndrome or another diagnosis, and they should not be managed as ordinary acne.

Topical Treatments: What Each Class Actually Does

Topical treatment is the foundation of care for almost everyone, and it works best as a deliberate combination of two mechanisms rather than one product used alone. I describe these by class rather than by brand, because the active ingredient is what matters and the same molecules are sold under many names.

• Topical retinoids (for example adapalene, tretinoin, trifarotene). These normalise the way the pore lining sheds, unplug existing comedones, prevent new ones and reduce inflammation. They are the backbone of long-term control and of maintenance after clearance. They cause dryness, flaking and sometimes an initial worsening in the first few weeks, and they are not used in pregnancy.
• Benzoyl peroxide. Reduces the skin bacterium involved in acne without encouraging bacterial resistance, which is why it is paired with antibiotics. It comes in several strengths, and lower strengths are often as useful and less irritating. It bleaches towels, pillowcases and clothing.
• Azelaic acid. Mildly unplugs pores, calms inflammation and helps post-inflammatory pigmentation. Useful for sensitive skin, and one of the options that can be considered in pregnancy and breastfeeding, which matters a great deal in this group of patients.
• Topical antibiotics (for example clindamycin, erythromycin). Anti-inflammatory and antibacterial, but never to be used alone or for months on end, because resistance develops. They are prescribed in fixed combination with benzoyl peroxide or a retinoid.
• Salicylic acid and other beta-hydroxy acids. Mild keratolytics, helpful as an adjunct for oily, congested skin, but not a substitute for a retinoid.
• Topical androgen receptor blockers. A newer class that blocks androgen signalling in the skin itself rather than throughout the body. Availability varies by country, and it is worth asking about where systemic hormonal treatment is unsuitable.

Current guidance, including the NICE recommendations on acne vulgaris, is built around a twelve-week trial of a fixed combination, typically a retinoid with benzoyl peroxide, or benzoyl peroxide with a topical antibiotic, applied to the whole affected area rather than dabbed on individual spots. That last point is the single most common application error. Acne forms in pores that look perfectly normal today, so treatment goes everywhere acne appears, including the jawline and neck, and including the chest and back if they are involved. Used properly and for long enough, a topical combination achieves a great deal on its own, and for many women it is the whole of the plan.

Irritation is managed rather than endured: start every other night, apply a bland moisturiser before or after the active product, use a gentle non-foaming cleanser, and use sunscreen daily, because retinoids and some oral antibiotics increase sun sensitivity and because sun exposure darkens post-inflammatory marks.

Hormonal Treatment: The Options and How They Are Chosen

Combined hormonal contraception is the usual first systemic choice for PCOS acne when topical treatment alone has not been enough and contraception is also wanted or acceptable, because it addresses the hormonal driver directly. The combined pill suppresses ovarian androgen production and raises SHBG, which lowers free testosterone; it also brings predictable bleeding, which protects the lining of the womb in women who ovulate infrequently.

The choice between preparations is made on the progestogen component and on your individual risk profile. Progestogens differ in how androgenic they are, and those with anti-androgenic or neutral activity are generally preferred when skin and hair are the main complaint, while the oestrogen dose is kept as low as is effective. Against that, some anti-androgenic progestogens carry a slightly higher venous thrombosis risk than older ones, so this is a genuine balance rather than an obvious winner, and it is a conversation to have with your own doctor rather than a decision to make from an article.

Before starting, your doctor will check for the situations in which combined hormonal contraception is not appropriate: migraine with aura, a personal history of venous thromboembolism or a significant clotting tendency, smoking at age 35 or over, uncontrolled high blood pressure, certain liver and gallbladder disease, current or past breast cancer, and the early postpartum period in some circumstances. Blood pressure, weight, and personal and family history are all part of that check.

Two practical expectations are worth setting. First, skin may be slightly worse in the first few weeks before it improves. Second, the pill controls the hormonal environment but does not unplug existing pores, so it is normally combined with topical treatment rather than used instead of it.

Progestogen-only methods are a different matter. They are valuable contraceptives, and the hormonal intrauterine system is a good way to protect the endometrium when periods are infrequent, a situation explained further in why you may not be ovulating and what helps. They do not, however, reliably improve acne, and in some women they make it worse. If your skin deteriorated after switching to a progestogen-only method, that is a recognised pattern and worth raising.

Anti-Androgen Options and Why Contraception Matters Alongside Them

Anti-androgens block androgen action at the receptor or reduce androgen production, and they are considered when topical treatment and combined hormonal contraception have not been enough, or when the pill is not suitable or not wanted. Because they interfere with androgen signalling, every one of them requires reliable contraception during treatment.

The most widely used is spironolactone, originally a diuretic, which blocks the androgen receptor and is prescribed off-label for acne and excess hair growth in many countries. It is taken daily, typically started low and increased, and it takes months rather than weeks to show its effect. Side effects are dose-related and include breast tenderness, irregular or breakthrough bleeding, light-headedness, increased urination and, less commonly, a rise in blood potassium. Potassium and kidney function are checked in women with kidney disease, those taking other drugs that raise potassium, and older patients; repeated routine testing is not necessary for every healthy young woman, but your doctor decides this individually. It is often combined with a combined pill, which both steadies the bleeding pattern and provides the contraception the drug requires.

Cyproterone acetate is a progestogen with strong anti-androgen activity, available in some countries combined with ethinylestradiol. It acts on androgenic skin and hair symptoms, but regulatory advice now restricts dose and duration because of a cumulative dose-related risk of meningioma, and liver toxicity is a recognised concern at higher doses. Finasteride, a 5-alpha-reductase inhibitor, and flutamide are used occasionally in specialist settings; flutamide in particular carries a risk of serious liver injury and is rarely chosen now.

Why contraception is not optional with these medicines

Androgens are essential for the normal development of the external genitalia in a male fetus. Blocking androgen action during pregnancy therefore carries a theoretical risk of incomplete masculinisation, so these medicines are avoided in pregnancy and reliable contraception is required throughout treatment and, for some of them, for a period afterwards. Practically, that means an anti-androgen is the wrong plan for anyone actively trying to conceive. If pregnancy is the goal now, the plan shifts towards topical treatment plus ovulation and cycle management instead, which I discuss in whether you can get pregnant with PCOS. If pregnancy is a goal for later, that is a reason to review the plan at intervals, not a reason to leave your skin untreated today.

Other Medicines That May Form Part of the Plan

Oral antibiotics, metformin and isotretinoin all have defined places in acne care, and none of them is a general-purpose solution for PCOS acne.

Oral tetracyclines such as doxycycline or lymecycline reduce inflammation and bacterial load in moderate to severe inflammatory acne, particularly when the chest and back are involved. They are prescribed for a limited period, around twelve weeks with a review, always together with a topical agent such as benzoyl peroxide or a retinoid, and never as a long-running solo treatment. They are also a useful non-hormonal route for women who cannot take or do not want hormonal treatment. Antibiotic stewardship is a real clinical consideration here, not bureaucracy. Tetracyclines are avoided in pregnancy, in breastfeeding and in young children, and they increase sun sensitivity.

Metformin improves insulin sensitivity and has an established role in the metabolic side of PCOS and in cycle regularity. Its effect on acne specifically is modest and inconsistent in the evidence, so it is best thought of as treatment for the underlying insulin problem that may help the skin indirectly, rather than as an acne drug. The same honest framing applies to supplements: inositol has been studied mainly for metabolic and ovulatory outcomes with limited and variable evidence quality, zinc has some supportive data in acne, and high-dose biotin or B12 can actually provoke acne-like eruptions. Unregulated hormone-balancing blends sold online are not a substitute for assessment.

Isotretinoin, an oral retinoid, is reserved for severe nodular or scarring acne, for acne causing significant psychological distress, and for disease that has not responded to adequate courses of other treatment. It is prescribed and monitored by a dermatologist under a pregnancy prevention programme, with pregnancy testing and strictly enforced contraception, because it is a powerful teratogen. Monitoring also covers liver function and lipids, and patients are counselled about dryness, muscle aches, sun sensitivity and the need to report any change in mood. One point is specific to PCOS: where androgen excess continues after a course finishes, relapse is more likely, so topical maintenance, and sometimes hormonal treatment, is often continued or started afterwards.

Procedures for the aftermath, such as chemical peels, microneedling and laser or light-based treatments for scarring and pigmentation, are considered only once active acne is controlled. Treating scars while inflammation is still running is both uncomfortable and illogical.

How Long Treatment Takes to Work

Acne treatment is measured in months, not days, and anyone who tells you otherwise is selling something. Realistic expectations are the difference between a plan that works and a drawer full of half-used tubes.

• Topical treatment. Weeks one to four are often the hardest: dryness, flaking, sometimes more spots as deeper lesions surface. A genuine change is usually visible around six to eight weeks, and twelve weeks is the point at which the trial is judged.
• Combined hormonal contraception. Expect at least three months before a fair assessment, and often around six for the fuller effect, with a possible early flare.
• Spironolactone and other anti-androgens. Two to three months for early change, and up to six months for the full effect at a stable dose.
• Oral antibiotics. Some improvement within six to eight weeks, with a formal review at around twelve weeks and no open-ended continuation.
• Post-inflammatory marks. Brown and red marks fade over months after the active lesion has gone, and faster with sun protection. True indented or raised scars do not fade with acne treatment and need separate management.

Two further points that patients are rarely told. First, improvement is not linear. Skin fluctuates with the cycle, so compare this month with the same week of a previous month rather than with yesterday. A photograph taken in the same light every four weeks is far more reliable than memory, which is heavily influenced by how you feel on the day.

Second, almost all of these treatments are controlling rather than curative. When treatment stops, the hormonal driver is still there, and acne commonly returns within a few months. Maintenance, usually a topical retinoid with or without continued hormonal treatment, is the part of the plan people abandon and then wonder why the problem came back. No treatment can be promised to clear the skin completely, and the honest aim is good, sustainable control with the fewest lesions and the least scarring.

Diet and Lifestyle: What the Evidence Supports

No diet cures PCOS acne, but the dietary change with the most consistent support is reducing the glycaemic load of what you eat, mainly because it acts on the insulin side of the problem. In practice that means less reliance on refined carbohydrate and sugary drinks, and more fibre, pulses, vegetables, protein and unsaturated fats, in a pattern close to a Mediterranean style of eating. It does not mean eliminating carbohydrate.

On dairy, the evidence is weaker and comes mostly from observational studies linking milk intake, particularly skimmed milk, with acne. That is an association rather than proof of cause, and the effect appears small. A reasonable approach is a personal trial: reduce milk intake for eight to twelve weeks while keeping everything else stable, and judge for yourself. Whey protein supplements are a more plausible aggravator and are easy to stop. Blanket elimination of entire food groups on the strength of a social media claim is not something I recommend, and in women with PCOS, who have a higher background rate of disordered eating, it carries real risk.

Weight deserves careful words. Where someone is carrying extra weight, a modest reduction improves insulin sensitivity, lowers free androgen levels and often restores more regular ovulation, and the skin may follow. But PCOS acne also occurs in slim women with entirely normal weight, and it is neither accurate nor kind to present weight as the explanation for everyone. If weight is part of your picture, the realistic and non-punitive approach is set out in how to lose weight with PCOS, and the dietary detail in the PCOS diet: what to eat and what to avoid.

• Build meals around protein, fibre and vegetables, and treat sugary drinks as the first thing to go
• Include both aerobic activity and resistance training, since muscle improves insulin sensitivity independently of any weight change
• Protect sleep, because short and disrupted sleep worsens insulin resistance and raises cortisol
• Address stress deliberately rather than aspirationally, as it is a genuine trigger for flares
• Stop smoking, which worsens skin healing as well as the cardiovascular risk profile that already needs attention in PCOS
• Be sceptical of supplements marketed for hormone balance, and tell your doctor about everything you take

It is worth being clear about what lifestyle change can and cannot do here. It acts on the insulin side of the problem, which for many women is the amplifier rather than the root cause, so it supports the treatment plan rather than replacing it. I have never yet seen a diet clear moderate inflammatory acne on its own, and presenting it that way simply shifts the blame onto the patient.

Skincare Mistakes That Make PCOS Acne Worse

Most of the self-inflicted damage I see comes from treating inflamed skin as though it were dirty skin. PCOS acne is not caused by poor hygiene, and aggressive cleaning makes it angrier.

• Over-washing and scrubbing. Twice daily with a gentle cleanser is enough. Grainy scrubs and brushes damage an already inflamed barrier.
• Alcohol-heavy astringents and several active products at once. Stacking an acid, a retinoid and a benzoyl peroxide wash produces irritation that looks like worsening acne, after which everything tends to get stopped at the same time.
• Skipping moisturiser and sunscreen. Both make effective treatment tolerable. Sunscreen also prevents the dark marks that often bother patients more than the spots did.
• Squeezing deep lesions. Nodules are too deep to extract, and pressure pushes inflammation sideways. It is a direct route to a lasting mark or a scar.
• Stopping at three weeks. This is the commonest reason a perfectly good regimen is said not to have worked.
• Using a topical antibiotic alone for months. It breeds resistance and loses effect. It belongs with benzoyl peroxide or a retinoid.
• Heavy occlusive make-up, and hair oils or pomades along the hairline and jaw. Choose non-comedogenic formulations and remove make-up properly.
• Home remedies. Lemon juice, toothpaste, baking soda and undiluted essential oils cause irritant and allergic reactions and leave pigmentation behind.
• Friction and occlusion. Chin straps, tight sportswear, unwashed pillowcases and a phone held against the jaw all contribute to mechanical acne in exactly the PCOS distribution.
• Topical steroid creams borrowed for red spots. They settle redness briefly and then produce a steroid-induced eruption that is harder to treat than the original problem.

One more habit worth naming: changing the whole routine every three weeks on the strength of a new recommendation. Acne treatment needs a stable regimen and an honest twelve-week assessment. Change one variable at a time.

When to See a Dermatologist as Well as a Gynaecologist

The two specialties manage different halves of the same problem, and for moderate or stubborn PCOS acne, shared care is usually better than either alone. A gynaecologist assesses and manages the hormonal and metabolic driver, cycle regularity, endometrial protection, contraception choice and fertility planning. A dermatologist assesses and manages the skin itself, grades severity, and holds the treatments that require specialist supervision.

It is worth asking for dermatology input if:

• There are nodules, cysts or any sign of scarring, now or in the past
• Twelve weeks of an appropriate topical combination has not produced a clear change
• The chest, back or shoulders are significantly involved
• Post-inflammatory pigmentation or early scarring is the main remaining concern
• Isotretinoin is being considered, or a previous course was followed by relapse
• The diagnosis is uncertain, or rosacea, perioral dermatitis, folliculitis or hidradenitis suppurativa is a possibility
• The acne is affecting your mood, sleep, work or social life, which is a clinical reason to escalate treatment rather than a question of vanity

Equally, see a gynaecologist or endocrinologist if periods are absent or come less often than roughly every six weeks, if hair growth or hair loss is progressing, if you are planning pregnancy, or if PCOS has been mentioned to you but never properly assessed. Acne is often the symptom that brings a woman through the door, and the assessment behind it protects cycles, fertility and long-term metabolic health as well as skin.

Seek medical advice promptly if

• Acne becomes suddenly severe with ulcerating or crusted lesions, fever or joint pain
• Virilising features develop over weeks to months, as listed earlier in this article
• You are taking a combined pill and develop calf pain or swelling, breathlessness, chest pain, a severe or unusual headache, visual disturbance, or weakness or numbness on one side
• You become pregnant, or suspect you might be, while taking an anti-androgen or isotretinoin. Stop the medicine and contact your doctor the same day
• Your mood deteriorates, or you have thoughts of harming yourself, at any point during treatment

Acne that has been dismissed for years as a purely cosmetic matter is, in PCOS, a visible sign of an endocrine condition with wider consequences. Treating the skin properly and assessing the condition behind it are the same piece of work, and both are worth doing.