Seborrheic Dermatitis

Slide 1 · Seborrheic Dermatitis

A clinicopathologic lecture

Morphology • Pathogenesis • Differential diagnosis

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · What this lecture will establish

Recognize characteristic distribution and lesion morphology

Explain multifactorial pathogenesis without assuming a single cause

Interpret acute and chronic histologic patterns

Differentiate close mimics and justify management principles

Slide 3 · An epidermal disease, not sebaceous-gland inflammation

Sebum-rich skin

Inflamed epidermis

Association ≠ identity

Slide 4 · A frequent chronic inflammatory dermatosis

Involvement of up to 5% of the general population

Often recurrent, especially in adulthood

Usually recognized from clinical pattern rather than laboratory assays

Slide 5 · Three diagnostic anchors

Typical sites: Scalp, central face, ears, presternal chest

Clinical appearance: Erythematous-yellow base with greasy scale

Histology: Spongiosis, acanthosis, and follicular parakeratosis

Slide 6 · The regional distribution is not random

Scalp

Dandruff / scale

Face

Glabella · nasolabial folds

Ear

Canal · postauricular

Trunk

Presternal chest

Folds

Axillae / intertriginous

Slide 7 · Why location provides diagnostic leverage

Multiple involved sebaceous-rich sites strengthen the clinical impression

Examination should extend beyond the most symptomatic area

Atypical distribution increases the importance of mimics

Slide 8 · Scalp disease includes dandruff

Dandruff is a common clinical expression on the scalp

Loose scale may dominate when erythema is subtle

Scalp inspection should include hairline and postauricular skin

Slide 9 · Facial localization follows a characteristic map

Central forehead

Glabella and eyebrows

Central face

Nasolabial folds

Lower face

Beard / moustache

Periorbital margin

Possible eyelid margin involvement

Slide 10 · The ears require active inspection

External auditory canal can be affected

Retroauricular erythema and scale may be easily overlooked

Fissures are particularly relevant behind the ears

Slide 11 · The chest may show conspicuous scaling

Presternal skin is a textbook-predilection site

Adult disease may involve anterior chest and upper trunk

Distribution and scale quality are often more useful than color alone

Slide 12 · Intertriginous disease extends the phenotype

Axillary, inframammary, and groin folds may be involved

Fold erythema can have less conspicuous scale

Consider Candida and other intertriginous dermatoses when morphology differs

Slide 13 · Infantile seborrheic dermatitis: Cradle cap

Greasy adherent scalp scale is a classic infant presentation

Can extend to axillary and diaper folds

Infants are often less troubled by pruritus than children with atopic dermatitis

Slide 14 · Infant and adult disease differ in course

Infantile

Cradle cap; Folds may be involved

Often self-limited

Gentle scale management

Adult

Scalp, face, ears, chest

Chronic relapsing tendency

Maintenance may be needed

Slide 15 · Clinical color varies with skin pigmentation

Erythema may appear pink, red, or less obvious on darker skin

Scale, distribution, and symptoms remain diagnostically useful

Avoid restricting recognition to one photographed skin tone

Slide 16 · Pruritus is variable rather than obligatory

Scalp discomfort and itching may occur

Minimal itch does not exclude active facial disease

Marked itch or exudation should prompt a wider differential

Slide 17 · The etiology is multifactorial and unresolved

No single necessary-and-sufficient mechanism has been established

Sebum, skin-resident yeast, epidermal barrier, and host response interact

Associations should not be presented as proven causal sequences

Slide 18 · Sebum: A permissive environment, not a diagnosis

Increased sebum production is a possible contributor

Androgen-dependent changes may influence sebaceous activity

Oily skin alone does not explain who develops dermatitis

Slide 19 · The acne comparison tests the sebum hypothesis

Increased sebum

Different inflammatory outcomes

Natural counterexample to sufficiency

Slide 20 · Parkinson disease provides clinical insight

Seborrheic dermatitis is more frequent in Parkinson disease

The Robbins account links dopamine deficiency with increased sebum

This observation supports—but does not prove—a sebum contribution

Slide 21 · Levodopa response is an association, not a therapy rule

In Parkinson disease, levodopa may reduce oiliness

Improvement of dermatitis has been observed in parallel

Do not extrapolate levodopa as seborrheic dermatitis therapy

Slide 22 · Malassezia is a plausible inflammatory cofactor

Malassezia yeasts may colonize sebaceous-rich skin

The organism is often part of the normal cutaneous microbiota

Presence alone does not demonstrate pathogenic causation

Slide 23 · The proposed Malassezia–lipase mechanism

Skin sebum lipids

Malassezia lipases

Free fatty acids

Inflammatory response

Proposed associations; Not a demonstrated linear pathway

Slide 24 · Barrier integrity helps explain individual susceptibility

Differences in epidermal barrier function may modify exposure

Altered barrier lipids could facilitate irritant responses

Barrier impairment complements rather than replaces the sebum–yeast model

Slide 25 · Host immune response shapes clinical severity

Inflammation is not explained by yeast quantity alone

Host cutaneous immune responses vary

The same ecological exposure may yield different phenotypes

Slide 26 · A defensible integrated pathogenesis model

Sebum-rich region

Yeast/lipid interactions

Barrier + host response

Erythema and scale

Proposed associations; Not a demonstrated linear pathway

Slide 27 · Severe HIV-associated disease is a clinical clue

Severe, treatment-refractory disease occurred with low CD4 counts

The frequency of this severe phenotype declined with effective ART

Severe atypical disease warrants assessment of clinical context

Slide 28 · Clinical phenotype: Color, texture, and contour

Erythematous-yellow base

Macules or papules

Greasy scale

Crusting

Slide 29 · What “greasy scale” adds to the examination

Scale character is one clue, not an isolated diagnostic test

Interpret scale together with site and erythematous base

Psoriasis and eczema may overlap clinically

Slide 30 · Retroauricular fissuring can be diagnostically useful

Fissures may develop behind the ears

Check both sides of the postauricular crease

Fissures also require assessment for irritation or infection

Slide 31 · Histology evolves as lesions persist

Earlier

Intercellular epidermal edema

More spongiotic pattern

Inflammatory scale may be focal

Later

Reactive epidermal thickening

More acanthotic pattern

Overlap with psoriasis can increase

Slide 32 · Spongiosis means intercellular epidermal edema

Intercellular edema

Spongiotic reaction pattern

Characteristic of earlier lesions

Schematic illustration — not a histologic specimen

Slide 33 · Acanthosis reflects reactive epidermal thickening

Expanded viable epidermis

Reactive thickening

More prominent in chronic lesions

Schematic illustration — not a histologic specimen

Slide 34 · Parakeratosis records altered cornification

Retained nuclei in surface scale

Altered keratinization

May localize to follicular openings

Schematic illustration — not a histologic specimen

Slide 35 · Follicular lipping is a characteristic clue

Parakeratotic mound

Follicular opening (ostium)

Neutrophils / serum may be admixed

Schematic illustration — not a histologic specimen

Slide 36 · The follicular ostium is the diagnostic landmark

Follicular infundibulum

Surface scale at the ostium

Assess adjacent epidermis

Schematic illustration — not a histologic specimen

Slide 37 · Neutrophils and serum may enter surface crust

Follicular parakeratotic mounds can contain neutrophils

Serous exudate contributes to crust formation

Neutrophils alone are not specific: Distribution matters

Slide 38 · Dermal inflammation is predominantly superficial

Superficial dermis

Perivascular inflammatory cells

Epidermal changes remain essential

Schematic illustration — not a histologic specimen

Slide 39 · Integrated biopsy interpretation

Reaction pattern

Follicular relationship

Inflammatory distribution

Slide 40 · Why scalp psoriasis is the closest mimic

Both can create scaling and erythematous scalp plaques

Both may show acanthosis and parakeratosis

Location alone is insufficient in isolated scalp disease

Slide 41 · Morphologic comparison with psoriasis

Seborrheic dermatitis

Follicular lipping / plugging

Spongiosis, especially early

Greasy or bran-like scale

Psoriasis

Regular elongated rete ridges

Suprapapillary thinning

Characteristic neutrophilic microabscesses

Slide 42 · Scalp biopsy evidence must be interpreted cautiously

A comparative study included 20 seborrheic dermatitis and 15 psoriasis cases

Follicular plugging and shoulder parakeratosis favored dermatitis

Its small, selected cohort does not yield a universal diagnostic rule

Slide 43 · Immunohistochemistry is not a routine separator

A published comparative scalp study tested several IHC markers

These stains did not improve differentiation in that cohort

Use clinicopathologic correlation rather than an invented immunophenotype

Slide 44 · Sebopsoriasis describes overlap—not a unique stain

Clinical features may overlap between the two entities

Consider typical lesions at other body sites

Do not force a categorical diagnosis when evidence is mixed

Slide 45 · Contact and atopic eczema are important mimics

All can show spongiotic inflammatory changes

Exposure distribution and clinical history are central

A biopsy pattern of spongiosis alone cannot specify etiology

Slide 46 · Tinea demands a different diagnostic pathway

Scaly disease may reflect a dermatophyte infection

Suspected fungal infection may warrant direct mycologic testing

Do not use Malassezia colonization as a surrogate for dermatophyte diagnosis

Slide 47 · Other facial and fold mimics require attention

Rosacea may produce central facial erythema

Candida can affect moist skin folds

Contact dermatitis can follow topical products or devices

Slide 48 · A focused differential diagnosis workflow

Distribution + scale

Examine associated clues

Targeted testing

Integrated diagnosis

Slide 49 · Diagnosis is usually clinical

Characteristic location and lesion appearance are central

The chronic or relapsing pattern provides context

Histology is an adjunct for uncertain or atypical cases

Slide 50 · When a biopsy adds value

Unexpected distribution or morphology

Poor response that raises an alternative diagnosis

Need to separate overlapping inflammatory reaction patterns

Slide 51 · Why a yeast-positive scraping is not definitive

Malassezia can exist on uninvolved normal skin

Microscopic detection does not automatically establish disease

Clinical inflammatory phenotype is the decisive context

Slide 52 · Therapy targets more than one disease component

Antifungal

Anti-inflammatory

Scale control / maintenance

Slide 53 · Antifungals have controlled-trial support

Cochrane 2015 reviewed 51 trials involving 9,052 participants

Topical ketoconazole and ciclopirox outperformed vehicle in relevant comparisons

Most studies had short follow-up; Sustained control remains less well studied

Slide 54 · Antifungal evidence is not absolute

Substantial between-study differences affect certainty

Claims of superiority among individual antifungals are limited

Short-term improvement should not be misrepresented as permanent cure

Slide 55 · Anti-inflammatory therapy reduces active inflammation

Topical corticosteroids can relieve erythema and scaling

Calcineurin inhibitors offer a nonsteroidal option for selected facial disease

Most randomized anti-inflammatory trials were short term

Slide 56 · The scalp often needs a vehicle-specific regimen

Medicated shampoos can deliver antifungal or keratolytic agents

Short anti-inflammatory courses may control exacerbations

Regimen selection depends on scalp tolerability and recurrence

Slide 57 · Face and ear treatment requires restraint

Topical antifungal creams are commonly used

Limit corticosteroid exposure on thin facial skin

Consider nonsteroidal anti-inflammatory alternatives when frequent therapy is required

Slide 58 · Gentle infant management is distinct

Regular gentle washing loosens scalp scale

Avoid traumatic scale removal

Escalate or reassess if presentation is extensive or atypical

Slide 59 · Relapsing disease requires follow-up planning

Explain the chronic or recurrent nature in adults

Adjust maintenance treatment according to distribution and flares

Reconsider diagnosis if the expected response is absent

Slide 60 · Clinical exercise: Greasy scale in typical sites

A patient has scaling of the scalp, glabella and nasolabial folds

Examination reveals yellowish scale over erythematous skin

Which distribution and morphologic findings support the diagnosis?

Discussion prompt; Explanation in presenter notes

Slide 61 · Clinical exercise: A refractory widespread eruption

A patient has extensive seborrheic-pattern dermatitis resistant to treatment

The clinical history includes possible immunosuppression

What associated conditions and diagnostic mimics require assessment?

Discussion prompt; Explanation in presenter notes

Slide 62 · Histology exercise: Ostial parakeratosis

Scalp biopsy has spongiosis, follicular parakeratotic mounds and a superficial infiltrate

Which constellation favors seborrheic dermatitis?

What histologic features would redirect toward psoriasis?

Discussion prompt; Explanation in presenter notes

Slide 63 · Seborrheic dermatitis: Integrated synthesis

A chronic inflammatory epidermal disorder with sebaceous-rich topography

Sebum, Malassezia, barrier and host response are interacting contributors

Follicular lipping and stage-dependent spongiosis/acanthosis support the biopsy

Clinical context remains essential for diagnosis and treatment

Slide 64 · Selected references

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026, Ch. 25.

DermNet. Seborrhoeic dermatitis. Updated 2024.

Park et al. Ann Dermatol. 2016;28:427–432.

Okokon et al. Cochrane CD008138 (2015).

Kastarinen et al. Cochrane CD009446 (2014).