🧴 Seborrheic Conditions Made Simple — A PLAB 2-Ready Guide for IMGs

Ann Augustin
Oct 7
3 min read

When you see a patient with itchy, scaly, or stuck-on lesions, the term seborrheic often appears in the notes. But what does it actually mean? And why do we use the same word for both a greasy dermatitis and a waxy skin growth?

Let’s simplify it once and for all 👇

🌿 The Word “Seborrheic” — What It Really Means

Origin:

Seb- / Sebo- → from sebum (Latin: “tallow,” “fat,” or “oil”)
-rrhea / -rrheic → from Greek rhein, “to flow”
So Seborrheic = related to the flow of sebum (skin oil)

In medicine, it describes conditions occurring in oily areas of skin — like the scalp, face, chest, and back.

🩺 The Four Common “Seborrheic” Conditions

Condition	Type	Typical Age	Main Sites	Key Feature
Seborrheic Dermatitis	Inflammatory	Adults	Scalp, face, chest	Red, greasy scales; itching
Infantile Seborrheic Dermatitis (Cradle Cap)	Inflammatory (mild)	Infants	Scalp	Yellow greasy crusts; non-itchy
Seborrheic Blepharitis	Inflammatory	Adults	Eyelid margins	Greasy flakes around lashes
Seborrheic Keratosis	Benign tumour	Middle-aged +	Trunk, face	“Stuck-on,” waxy plaques

🔬 Pathophysiology — What’s Happening Beneath the Skin

1️⃣ Seborrheic Dermatitis

Trigger: Overgrowth of Malassezia yeast on oily skin
Mechanism: The yeast breaks down sebum → releases irritating fatty acids → body mounts an inflammatory response
Result: Redness, scaling, and itch in sebaceous areas
Common associations: Parkinson’s disease, HIV, stress, winter flares

🧠 Exam Tip: When describing a patient, mention both site (e.g. scalp and nasolabial folds) and character (greasy, yellow scales).

2️⃣ Infantile Seborrheic Dermatitis

Cause: Temporary over-activity of infant sebaceous glands from maternal hormones
Plus: Malassezia colonisation adds mild inflammation
Outcome: Self-limiting by 6–12 months

👶 Reassure parents: “It looks greasy but it’s harmless and will clear on its own.”

3️⃣ Seborrheic Blepharitis

Mechanism: Extension of seborrheic dermatitis to eyelids → inflammation of Meibomian glands → flaky debris at lash bases
Complication: Chronic irritation or dry eyes

💡 PLAB communication point: Advise on lid hygiene — “Clean the eyelid edges daily with warm water and diluted baby shampoo.”

4️⃣ Seborrheic Keratosis

Completely different!A benign clonal proliferation of epidermal keratinocytes, not related to sebum.
Genetic mutations: FGFR3 / PIK3CA / TERT promoter
Appearance: Waxy, “stuck-on” plaque, tan-to-black, sometimes scaly
Why the name? Early dermatologists thought it came from oily skin regions → called it seborrheic — but that’s a historical misnomer.
Why it looks greasy: Built-up keratin reflects light, giving a wax-like shine.

⚠️ Leser–Trélat Sign: Sudden eruption of multiple lesions may indicate an internal malignancy (e.g. gastric adenocarcinoma).

🧠 Quick Comparison Table

Feature	Seborrheic Dermatitis	Infantile Seborrheic	Seborrheic Blepharitis	Seborrheic Keratosis
Pathology	Inflammatory reaction to Malassezia	Hormonal + yeast	Eyelid gland inflammation	Benign keratinocyte growth
Inflammatory?	✅	✅ (mild)	✅	❌
Itchy?	Often	Rarely	Mild	Rarely
Infectious?	❌	❌	❌ (may have bacteria)	❌
Treatment	Ketoconazole + low-potency steroid	Emollients, mild shampoo	Lid hygiene, topical antibiotic if needed	Cryotherapy, curettage if cosmetic
Prognosis	Chronic & recurrent	Resolves spontaneously	Chronic but manageable	Benign & stable

💬 PLAB 2 Clinical Reasoning & Communication Pearls

Scenario	Key Phrases
Adult with flaky scalp and red patches	“This is likely seborrheic dermatitis, which is an inflammation of the skin in oily areas. It’s not contagious and responds well to medicated shampoo.”
Worried parent of a baby	“Cradle cap is very common and not painful. You can soften the scales with baby oil and gently wash them away.”
Elderly patient with new dark spot	“This looks like a seborrheic keratosis, which is a harmless age-related skin growth. I’ll check the borders and colour to be sure it’s benign.”
Exam tip for communication	Always reassure about non-infectious, non-contagious nature, and discuss cosmetic options sensitively.

🧠 Key Take-Home Points

“Seborrheic” = relating to oily areas, not necessarily sebum itself.
Seborrheic dermatitis → inflammation; seborrheic keratosis → proliferation.
Malassezia yeast = main culprit in dermatitis; keratinocyte mutation = cause of keratosis.
The “greasy” or “waxy” look is from keratin and light reflection, not oil.
Always consider the Leser–Trélat sign if multiple keratoses erupt suddenly.

📚 References