Acne: causes, types and how it's treated

Acne develops when the sebaceous glands produce too much sebum and the follicles become blocked by dead skin cells, creating the environment where bacteria thrive. It is the most common skin disease of all: around 85% of people aged 12 to 24 are affected, according to the American Academy of Dermatology. Treatment ranges from topical products to oral antibiotics, isotretinoin or dermatological procedures, depending on severity and lesion type. The earlier it is treated, the lower the risk of permanent scarring.

Are acne, spots and blackheads the same thing?

No, and the confusion is common.

Acne is the name of the disease. Blackheads and spots are two kinds of lesion that the disease produces.

Blackheads are comedones. When the follicle is open at the surface, the sebum oxidises and darkens: that is the blackhead. When it stays closed, a whitehead forms under the skin.

Spots are the inflamed lesions — papules and pustules — red, raised and sometimes painful. They appear when a blocked follicle becomes inflamed.

Having the odd blackhead is not the same as having acne. Acne is the persistent picture, with multiple lesions and a tendency to recur.

What is acne?

Acne vulgaris is a chronic inflammatory disease of the pilosebaceous unit. Four mechanisms combine to produce the lesions: increased sebum production, altered follicular keratinisation, colonisation by Cutibacterium acnes, and inflammation.

It is a disease, not a cosmetic problem. Quality-of-life studies place the psychological burden of moderate to severe acne at levels comparable to asthma or epilepsy.

About the bacterium: Cutibacterium acnes lives normally on everyone's skin. It is not an infection caught from outside. What happens in acne is that the environment inside a blocked follicle encourages it to multiply and triggers inflammation. This is why acne is not contagious and does not pass from person to person.

What causes acne?

Hormones. Androgens stimulate the sebaceous glands. This explains why acne appears at puberty, why it worsens in the week before menstruation, and why it can emerge or worsen during pregnancy, with the hormonal shift.

Genetics. Having a parent with a history of severe acne raises the likelihood of developing the same form.

Medication. Corticosteroids, lithium, some antiepileptics and certain contraceptives can trigger acneiform eruptions. The timing relative to starting the drug is the clue.

Associated conditions. Polycystic ovary syndrome often presents with acne that resists standard treatment, particularly alongside irregular periods or hirsutism.

External factors. Pollution, high humidity and mechanical occlusion of the skin.

What is hormonal acne, and how is it treated?

Hormonal acne is the picture in which androgen influence dominates. It is recognised by a typical pattern: inflammatory lesions on the lower third of the face, along the jawline, chin and neck, flaring cyclically before menstruation.

It appears mostly in adult women, often after the age of 25 and with no history of teenage acne. It tends to respond poorly to the treatments used for adolescent acne.

Treatment relies on medication with antiandrogenic action — a suitable combined contraceptive or spironolactone — alongside topicals. Where there is menstrual irregularity, excess hair growth or difficulty conceiving, investigating polycystic ovary syndrome is warranted.

Which types of acne are there?

Acne vulgaris. The usual form, with comedones, papules and pustules.

Acne conglobata. A severe form with confluent nodules and sinus tracts. Predominant in young men, and scarring.

Acne fulminans. Sudden onset with fever, malaise and ulcerated lesions. Rare, and requires urgent assessment.

Neonatal acne. Appears in the first weeks of life in many newborns and resolves on its own, without treatment. It leaves no marks.

Infantile acne. Emerges between three months and four years, or persists beyond the neonatal period. Warrants assessment, as it may signal an endocrine disorder.

Mechanical acne. Caused by friction and occlusion: backpack straps, helmets, tight uniforms, masks.

Cosmetic acne. Triggered by comedogenic products.

Occupational acne. From exposure to mineral oils and chlorinated hydrocarbons at work.

What is acne excoriée?

In acne excoriée, the lesions you see are no longer those of the disease: they are the result of picking at them. Squeezing or scratching turns a papule that would have cleared in days into a wound that takes weeks and leaves a mark.

The behaviour is usually automatic, done at the mirror and without full awareness, and is associated with anxiety or compulsive behaviour. It is more common in women.

Treating the acne alone does not solve it, because the main lesion is self-inflicted. Effective treatment combines controlling the acne with addressing the behaviour, and in some cases benefits from psychological support. It is not a lack of willpower, and recognising that is usually the first step.

Which lesions appear, and where?

Non-inflammatory lesions are the comedones: open ones are blackheads, closed ones are whiteheads. Inflammatory lesions are papules and pustules, raised and tender. In severe forms, nodules and cysts appear, and these are the ones that scar.

Distribution follows the density of sebaceous follicles: face, neck, upper chest, back and shoulders.

Does diet affect acne?

For years the answer was a flat no. The current evidence is more nuanced.

American Academy of Dermatology guidelines recognise an association between high-glycaemic-index diets and worsening acne. There are also data pointing to skimmed milk as an aggravating factor in some patients, though the mechanism remains unclear.

What has not held up: chocolate, fats and fried food as direct causes.

The reasonable reading is this. Diet does not cause acne, but it can worsen it in predisposed people. Changing what you eat is not a substitute for treatment.

What about hygiene? And the sun?

Hygiene. Acne is not caused by poor cleansing. Washing too often, or with harsh products, damages the skin barrier and makes things worse. Twice a day with a gentle cleanser is enough.

Sun. Sun exposure dries the lesions and improves appearance for a few days. Then comes the rebound: the stratum corneum thickens and follicular obstruction worsens. Add the cumulative skin cancer risk and the darkening of post-inflammatory marks, which deepen with exposure.

What is the best treatment for acne?

There is no universally best treatment. There is the treatment suited to each lesion type, to the severity and to the impact on the person's life — and that is what a consultation is for.

Topical. Retinoids, benzoyl peroxide, azelaic acid, topical antibiotics. First line in mild to moderate acne. Over-the-counter creams can help in mild cases, but do not replace prescription treatment when inflammatory lesions persist.

Oral. Tetracycline-class antibiotics in limited courses. Contraceptives with antiandrogenic effect, or spironolactone, in selected women. Isotretinoin for severe, nodulocystic or resistant acne, always with effective contraception and laboratory monitoring.

Procedures. Chemical peels, comedone extraction, laser and light. These complement rather than replace.

Scarring. Microneedling, fractional laser, subcision and fillers, depending on scar type. Scar treatment only begins once the acne itself is controlled, and the number of sessions varies with the depth and extent of the scarring — which is why the plan and the cost are set after an in-person assessment.

Results take time. Almost every treatment needs six to twelve weeks before it can be judged, and an initial flare is common. Giving up after a fortnight is the most frequent mistake.

Can acne be cured?

Acne is controlled; it is not permanently eliminated by any single act.

It is a chronic disease, with periods of flare and remission. With the right treatment it is possible to reach skin free of active lesions and keep it that way, and most people improve substantially after adolescence.

Isotretinoin comes closest to prolonged remission: a significant proportion of patients never have meaningful acne again after a full course. Even so, some need to repeat it, and the decision is always clinical.

Be wary of any promise to eliminate acne for good. In medicine, outcomes depend on individual factors, and no serious practitioner guarantees a result.

What is the doctor who treats skin called?

A dermatologist. The medical specialist in diseases of the skin, hair and nails, with specific training after medical school.

In Portugal, the specialty recognised by the Ordem dos Médicos is Dermatovenereology — dermatology and venereology. When choosing, check that the practitioner holds a registered specialty.

When should I see a dermatologist?

• When nodules or cysts appear

• When there are already scars or marks

• When three months of appropriate care have changed nothing

• When acne is affecting social life or mood

• When you cannot stop picking at the lesions

• When it appears suddenly in an adult, particularly with irregular periods or excess hair growth

Dr Ellene Papazis is a dermatologist accredited in Portugal and Brazil, and treats patients with acne in Porto, Portugal, both in person and online.

Sources

• American Academy of Dermatology — Guidelines of care for the management of acne vulgaris, JAAD, 2024

• European Academy of Dermatology and Venereology — European acne treatment recommendations

• Portuguese Society of Dermatology and Venereology (SPDV)

• Global Burden of Disease Study — skin disease prevalence data

Written and reviewed by Dr Ellene Papazis, dermatologist accredited in Portugal and Brazil. Consultations in Porto, Portugal.

Updated 25 July 2026.