Seborrhoeic dermatitis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Scale can be greasy yellow, white or powdery. Underlying inflammation may look pink-red, purple, grey, darker or lighter than surrounding skin, and residual dyspigmentation may persist. Ask about itch and flare rather than equating pigment contrast with current severity.

Select vehicle by site: shampoo for scalp and hair-bearing trunk, cream for face or chest, and mild anti-inflammatory only for a brief active flare. Explain maintenance because recurrence is expected. Reconsider HIV testing or neurological assessment only when severity, risk and other symptoms justify it, with consent rather than routine assumptions.

Seborrhoeic dermatitis care should combine visible inflammation with itch, pain, sleep, occupation and treatment burden. Agree where each product goes, how much is used and when response will be reviewed; explain urgent features separately so normal fluctuation is not confused with infection or treatment failure.

Key points

Adult seborrhoeic dermatitis affects scalp, eyebrows, nasolabial folds, ears and central chest with scale and erythema, lighter or darker change.
Cradle cap is usually self-limited and gently managed; an unwell infant, widespread eruption or growth failure needs paediatric assessment.
Ketoconazole shampoo reduces scalp Malassezia: use twice weekly for two to four weeks, leave three to five minutes, then once every one to two weeks for prevention.
Ketoconazole 2% cream can be applied once or twice daily for two to four weeks to adult facial or body disease, then intermittently for maintenance.
Use only a short course of mild topical corticosteroid for troublesome inflammation on face or folds; repeated potent facial use causes avoidable harm.
Patchy hair loss, broken hairs or a boggy plaque is not simple dandruff and requires assessment for tinea capitis.
For Seborrhoeic dermatitis, document body sites, severity, sleep and function, recent treatment, infection features and what the patient can realistically apply each day.
In Seborrhoeic dermatitis, reassess the diagnosis when a well-used, correctly potent regimen fails rather than repeatedly intensifying treatment without examining adherence, exposure and mimics.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Malassezia interaction

Normal lipid-dependent Malassezia yeasts and their metabolites interact with sebaceous skin, barrier susceptibility and host immunity; the condition is inflammatory rather than a contagious fungal infection.

Age and sebum context

Cradle cap occurs in early infancy, while adult disease clusters after puberty and in sebaceous zones where lipid environment supports yeast activity.

Host associations

HIV, Parkinson disease and some neurological or immunosuppressive states increase prevalence or severity, although most patients have no underlying systemic disorder.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Lipid metabolite irritation
Malassezia lipases release free fatty acids from sebum, and susceptible epidermis develops irritation, altered differentiation and scale.
2
Barrier and immune response
Impaired barrier and exaggerated local inflammation create erythema or pigment change, itch and recurrent greasy or powdery scale.
3
Sebaceous distribution
High-density sebaceous areas including scalp, eyebrows, glabella, nasolabial folds, ears and central chest shape the characteristic map.
4
Relapsing ecology
Antifungal treatment reduces yeast burden and inflammation temporarily, but normal recolonisation and host susceptibility explain recurrence after treatment stops.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Scalp spectrum

Fine dandruff through adherent greasy scale occurs diffusely without the broken hairs or focal alopecia expected in tinea capitis.

Facial sebaceous map

Eyebrows, glabella, nasolabial folds, beard area and ears develop symmetrical scale with erythema or relative pigment change.

Chest and fold disease

Petaloid or arcuate scaly plaques can affect presternal skin, axillae and groins and may resemble psoriasis or candidiasis.

Infant cradle cap

Thick greasy scalp scale in a thriving comfortable infant usually resolves, but generalised disease or poor growth changes the assessment.

Kerion warningRed flag

Tender boggy scalp swelling, pustules, lymphadenopathy or hair loss suggests inflammatory tinea and risks permanent scarring.

Red flags requiring action

Erythroderma, fever, failure to thrive, severe eye involvement, extensive disease with immunosuppression, neurological decline or treatment-resistant atypical plaques warrants broader assessment.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Clinical distribution and scalp examinationFirst step
Why
Confirm a sebaceous-zone pattern and look for hair-shaft or nail clues to alternatives.
Interpretation and limitations
Examine the whole scalp, eyebrows, ears and chest; treatment can suppress scale and make a partly treated pattern less specific.
02
Hair and scale mycology
Why
Assess tinea capitis or dermatophyte infection when alopecia, broken hairs or annular borders occur.
Interpretation and limitations
Collect abnormal hairs and active scale before antifungal therapy when possible; negative testing is limited by specimen quality.
03
HIV testing with consent when indicated
Why
Investigate new severe or unusually extensive disease with compatible risk, infection or systemic features.
Interpretation and limitations
Seborrhoeic dermatitis alone is common and nonspecific; testing should follow ordinary consent and risk assessment.
04
Skin biopsy for persistent atypical plaque
Why
Exclude psoriasis, lupus, lymphoma or another infiltrative disorder when morphology is discordant.
Interpretation and limitations
Histology is not routine and should target an untreated representative edge with a precise differential.
05
Eye assessment
Why
Identify blepharitis, conjunctival inflammation or another cause of painful eye symptoms.
Interpretation and limitations
Lid-margin scale supports blepharitis; photophobia, reduced vision or corneal pain requires urgent ophthalmic review.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Scalp psoriasis

Thicker sharply demarcated scale extending beyond the hairline, extensor plaques or nail changes support psoriasis, while overlap can produce sebopsoriasis.

Tinea capitis

Patchy alopecia, broken hairs, black dots, lymph nodes or inflammatory kerion requires mycology and prompt systemic antifungal treatment.

Atopic or contact dermatitis

Greater dryness, flexural history or a product-linked facial and eyelid distribution suggests atopy, irritancy or delayed contact allergy.

Cutaneous lupus or malignancy

Persistent scar, dyspigmentation, follicular plugging, ulceration or a unilateral infiltrated plaque should trigger biopsy or specialist review.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Adult scalp diseaseReduce scale and prevent recurrenceFirst stepDandruff or seborrhoeic scalp inflammation occurs without alopecia, kerion or systemic illness.

1Use ketoconazole 2% shampoo twice weekly for two to four weeks, massaging into wet scalp and leaving for three to five minutes before rinsing.
2Add a short site-appropriate anti-inflammatory scalp preparation when itch and inflammation remain prominent after scale control.
3Once controlled, use ketoconazole shampoo every one to two weeks and review adherence or diagnosis if no improvement by four weeks.

02Face or body diseaseCombine antifungal and brief anti-inflammatory careTypical plaques affect nasolabial folds, eyebrows, ears or central chest without red flags.

1Apply ketoconazole 2% cream once or twice daily for two to four weeks and continue for a few days after symptom clearance.
2Use hydrocortisone 1% very briefly on selected inflamed facial sites, avoiding eyelids and infection and following the shorter product licence.
3Step down to intermittent antifungal maintenance, gentle cleansing and a light non-irritant emollient that the patient can use consistently.

03Atypical or severe diseaseTest the mimic and host contextDisease is focal with alopecia, unilateral, scarred, treatment-resistant, widespread or associated with systemic concern.

1Obtain appropriate mycology for hair loss or active borders and arrange urgent care for kerion rather than applying more corticosteroid.
2Consider biopsy, patch testing, HIV testing or neurological assessment only from the specific clinical context and with consent.
3Refer dermatology when diagnosis remains uncertain, ordinary regimens fail despite correct use or recurrent disease substantially impairs life.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Licensed treatment and prophylaxis for dandruff and seborrhoeic dermatitis through antifungal and local anti-inflammatory effects in hair-bearing sites.

Ketoconazole 2% shampoo

Adults and adolescents wet hair and scalp, lather, leave for three to five minutes and rinse; use twice weekly for two to four weeks, then once every one to two weeks.

Avoid eye contact and stop for significant irritation or hypersensitivity; review diagnosis if not clear by four weeks and taper prolonged topical steroid while introducing shampoo.

Licensed topical antifungal for adult facial and body seborrhoeic dermatitis where Malassezia reduction helps control recurrent inflammation.

Ketoconazole 2% cream

Adults apply to affected and immediately surrounding skin once or twice daily for two to four weeks; intermittent once-weekly maintenance may then be used.

Keep from eyes, check excipient irritation and reconsider diagnosis after four weeks without improvement; extensive or immunocompromised disease may require specialist review.

Brief mild anti-inflammatory treatment for troublesome facial or fold inflammation alongside antifungal care, not continuous relapse prevention.

Hydrocortisone 1% cream

Adults apply thinly once or twice daily for up to seven days under this product licence, using only a small amount on selected inflamed sites.

Avoid eyelids, untreated infection and prolonged facial or flexural exposure; review atrophy, perioral change and rebound, and do not use in infants without age-specific direction.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Secondary infection

Excoriated or fissured skin may become bacterially infected, while an inflammatory scalp kerion mislabelled seborrhoeic dermatitis risks scarring hair loss.

Ocular surface disease

Blepharitis can produce gritty eyes, crusted lid margins and recurrent inflammation requiring eye hygiene or specialist assessment when painful or vision-affecting.

Psychosocial visibility

Persistent scalp flaking and facial colour change affect confidence, work and social interaction despite limited body surface.

Missed systemic association

New severe or extensive adult disease can be a clue to immunosuppression or neurological disease when accompanying history supports investigation.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Review scalp response after four weeks, checking contact time, frequency, hair loss and whether scale extends beyond the expected distribution.
For facial disease, record steroid days separately from antifungal maintenance to prevent continuous unnoticed corticosteroid exposure.
Reassess host factors only when disease severity, recurrence and accompanying symptoms remain disproportionate.
At review of Seborrhoeic dermatitis, compare itch, sleep, fissuring or ooze, affected sites, function and treatment use with the agreed baseline.
For Seborrhoeic dermatitis, record adverse effects, new contact exposures and the safety-net for pain, fever, rapidly spreading disease, eye symptoms or systemic illness.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Malassezia is normal flora

The disease reflects host–yeast interaction, so antifungal use does not mean the patient has acquired a contagious infection.

Maintenance matches recurrence

Intermittent shampoo after clearance reduces relapse because stopping all treatment permits ordinary yeast ecology to re-establish.

Pigment may outlast scale

Darker or lighter facial patches can persist after itch and flaking settle and should not trigger indefinite corticosteroid use.

Cradle cap differs from adult disease

Infant scalp scale usually resolves spontaneously and does not justify copying an adult antifungal-steroid regimen.

Hair loss changes urgency

Broken hairs, black dots and boggy inflammation point to tinea capitis, which needs systemic rather than shampoo-only treatment.

11Common pitfallsFrequent interpretation and management errors.

01
Using potent topical corticosteroid continuously on nasolabial folds because the eruption returns.
02
Calling patchy alopecia and lymphadenopathy severe dandruff without obtaining mycology.
03
Interpreting post-inflammatory facial pigment change as active treatment failure.
04
Screening every patient for HIV solely because common mild dandruff is present.
05
Stopping ketoconazole immediately after improvement without discussing safe intermittent maintenance.