Seborrheic dermatitis
Synonyms and keywords: Seborrheic eczema; Seborrhea; Cradle cap

# Overview
Seborrheic eczema (also known as Seborrheic dermatitis, seborrhea) is a skin disorder affecting the scalp, face, and trunk. Seborrheic dermatitis causes flaky, itchy, red skin and temporary hair loss. It particularly affects the sebum-gland rich areas of skin. Causes of seborrheic dermatitis include Malassezia furfur (formerly known as Pityrosporum ovale) as well as genetic, environmental, hormonal, and immune-related factors. Medical therapy for seborrheic dermatitis includes antifungal agents, corticosteroids, and lithium salts.

# Historical Perspective
- In 1887, seborrheic dermatitis was first described by Unna.
- In 1894, a hypothesis was made by Unna and Sabouraud that causative agents responsible for seborrheic dermatitis include yeast Malassezia, bacteria, or both as they were obtained in high quantities in cultures obtained from the affected patients.
- In 1984, Shuster discovered that seborrheic dermatitis can be treated with oral ketoconazole..

# Classification
There is no established classification system for seborrheic dermatitis. However, it may be classified according to the anatomical location, age group, symptoms, etiology and severity.

## Classification by Anatomy
Seborrheic dermatitis may be classified on the basis of anatomical location into following types:
- Localized
Scalp: Most common presentation in  infants known as cradle cap
Face: Most commonly involves eyelids, eyebrows, and nasolabial folds
Retroauricular
Body folds: Commonly affects axilla, breast folds, and inguinal area
Trunk: May be seen in severe cases and most common site of involvement is lower abdomen
Upper Chest: Most commonly seen in adults
Pityriasiform: Oval macules and patches.
Petaloid type: Small papules with oily scales may enlarge to become patches resembling petals of flower.
- Scalp: Most common presentation in  infants known as cradle cap
- Face: Most commonly involves eyelids, eyebrows, and nasolabial folds
- Retroauricular
- Body folds: Commonly affects axilla, breast folds, and inguinal area
- Trunk: May be seen in severe cases and most common site of involvement is lower abdomen
- Upper Chest: Most commonly seen in adults
Pityriasiform: Oval macules and patches.
Petaloid type: Small papules with oily scales may enlarge to become patches resembling petals of flower.
- Pityriasiform: Oval macules and patches.
- Petaloid type: Small papules with oily scales may enlarge to become patches resembling petals of flower.
- Generalized: Mostly seen in infants; it is associated with Leiner's disease and children with severe immunodeficiency.

## Classification by Age
- Infantile: Occurs in first three months of life.
- Adults: Occurs most commonly between 30-60 years of age.

## Classification by Symptomatic Presentation
- Non pruritic: Most commonly occurs in infants
- Pruritic: Most commonly occurs in older children and adults

## Classification by Etiology
- Idiopathic
- Infectious
- Autoimmune / Inflammatory

## Classification by Severity
- Mild to moderate disease: Occurs in immunocompetent individuals
- Severe disease: Occurs in immunocompromised individuals

# Pathophysiology
The exact pathophysiology of seborrheic dermatitis remains unclear. However, several mechanisms are hypothesized to play a role in pathogenesis of seborrheic dermatitis. 

## Pathogenesis
Hypotheses regarding the pathogenesis of seborrheic dermatitis include:
Hypotheses related to Malassezia :
- A strong correlation between presence of the fungal yeast Malassezia and response to antifungals in patients with seborrheic dermatitis.
- Malassezia is a lipophilic yeast found  on the skin of both healthy individuals and seborrheic dermatitis patients. It is thought that host reaction to Malassezia or its metabolites causes an inflammatory reaction that may have a significant role in the process..
- Another proposed mechanism for seborrheic dermatitis suggests that a disrupted lipid layer of Malassezia leads to an increased production of pro inflammatory cytokines such as IL-6 and IL-7, and decreased production of IL-10. 
- Malassezia is seen to have lipase activity, which acts on cutaneous triglycerides causing a release of unsaturated fatty acids such as arachidonic acid. These metabolites may cause abnormal proliferation and differentiation of the stratum corneum leading to signs and symptoms of seborrheic dermatitis.
Other Hypotheses
- Sebaceous gland activity
- Immune response
- Epidermal barrier dysfunction
- Corneocyte shape
- Corneodesmosomes
- Disrupted lipid lamellar structure 
- Neurogenic and other factors

## Genetics
There is no specific genetic cause for seborrheic dermatitis..

## Associated conditions
- Parkinsonism
- Epilepsy
- Depressive mood disorder
- Traumatic brain injury
- Spinal cord injury
- HIV
- Lymphoma
- Downs syndrome

## Gross Pathology
Superficial flaking and redness are characteristic findings of seborrheic dermatitis.
- Seborrheic dermatitis showing erythema on face. - By Roymishali - Own work, CC BY-SA 3.0, 
- Upper chest showing redness and crusting. - Adapted from Dermatology Atlas.

## Microscopic Histopathology
Histopathological findings of seborrheic dermatitis may be categorized into the following stages: 
- Acute
- Focal mild spongiosis with superficial crust containing neutrophils.
- Edema of papillary dermis.
- Dilatation of blood vessels in superficial vascular plexus with  infiltration of lymphocytes, histiocytes.
- Subacute
- Psoriasiform hyperplasia.
- Keratin showing presence of yeasts.
- Chronic
- Extensive psoriasiform hyperplasia
- Minimal spongiosis
- Follicular crusting

# Causes
The cause of seborrheic dermatitis remains unknown; however, the following factors may have been implicated:
- Malassezia furfur (formerly known as Pityrosporum ovale).
- Excessive vitamin A
- Lack of biotin,
- pyridoxine (vitamin B6)
- riboflavin (vitamin B2)

# Differentiating Seborrheic dermatitis from Other Diseases
Symptoms of seborrheic dermatitis may overlap with other skin conditions such as psoriasis, candidiasis, contact dermatitis, and atopic dermatitis. Differential diagnosis of seborrheic dermatitis may be classified into two types by age group:

## Differential diagnosis in Infants
- Atopic dermatitis
- Candidiasis
- Dermatophytosis
- Diaper dermatitis
- Langerhans cell histiocytosis
- Psoriasis
- Pityriasis amiantacea
- Rosacea
- Tinea capitis
- Zinc deficiency
- Vitamin B deficiency

## Differential diagnosis in Adults
- Systemic lupus erythematosus
- Candidiasis
- Erythrasma
- Contact dermatitis
- Psoriasis
- Tinea versicolor
- Tinea corporis
- Secondary syphilis
- Pemphigus foliaceus
- Rosacea

# Epidemiology and Demographics

## Epidemiology
Worldwide, the prevalence of seborrheic dermatitis is estimated to be 11000 cases per 100,000. Prevalence of seborrheic varies among individuals based on the following factors:
- Higher reporting of mild cases
- Higher in patients with HIV with 35000 per 100,000 in early diagnosis and 85000 per 100,000 with full blown AIDS
- Higher prevalence seen among those directly exposed to UV radiation
- The exact incidence of seborrheic dermatitis is unknown

## Demographics

### Age
Seborrheic dermatitis demonstrates a tri-modal age distribution as follows:
- The first incidence peak is seen in infants around three to four months of age, which usually resolves within 12 months
- The second incidence peak is seen around puberty.
- The third incidence peak is seen after age 50 with the highest prevalence seen among ages 33-44 years.
- Age groups showing lowest prevalence of clinical disease is seen in individuals younger than 12 years.

### Gender
Males are more commonly affected with seborrheic dermatitis than females.

### Race
- Seborrheic dermatitis is rarely seen in African Americans.
- If seborrheic dermatitis is seen in this population, it leads to high suspicion of HIV in affected individuals.

# Risk Factors
The most common risk factors for seborrheic dermatitis include:
Immunosuppression
- Organ transplant recipients
- HIV/AIDS
- Malignancies such as lymphoma
Neurologic and psychiatric cases
- Parkinsonism
- Depression
- Tardive dyskinesia
- Traumatic brain injury
- Epilepsy
- Facial nerve palsy
- Spinal cord injury
Genetic disorders
- Downs syndrome
- Hailey-Hailey Disease
- Cardiofaciocutaneous syndrome
- Mutation in (ZNF750) coding a zinc finger protein (C2H2)
Other risk factors
- Stress
- Treatment with psoralene and UV-A
- Male gender 
- Obesity
- Diabetes mellitus
- Seasonal changes such as low temperature and decreased humditiy
- Drugs such as haloperidol deconate, lithium and chlorpromazine

# Screening
There are no screening guidelines for seborrheic dermatitis.

# Natural History, Complications, and Prognosis

## Natural History
- The symptoms of seborrheic dermatitis usually develop in the first three months in infants. It may resolve without treatment in most cases in few months and rarely presents after 12 months.
- In adults, symptoms of seborrheic dermatitis usually develop in the second and third decade of life, and start with symptoms such as redness, scaling and crusting on affected areas. However, occurrence of seborrheic dermatitis is highly variable and it may present after 50 years of age.
- The course of disease is highly variable among individuals despite treatment. Some cases present with more frequent relapses than others.

## Complications
Common complications of seborrheic dermatitis include:
- Temporary or permanent hair loss
- Secondary bacterial infection
- Blepharitis
- Abscess of meibomian glands
- Otitis externa
- Extensive involvement of body

## Prognosis
- The prognosis of seborrheic dermatitis is excellent in infants; it is a self limited disease and usually resolves within few months after birth.
- In adults, it is a recurrent condition with no permanent cure.

# Diagnosis
There is no definitive diagnostic criteria for seborrheic dermatitis. Diagnosis of seborrheic dermatitis is primarily clinical; it is based on history and physical examination findings.

# History
Obtaining complete  history is important in making diagnosis of seborrheic dermatitis as it will give an insight into cause and associated risk factors for the disease. In addition to symptoms of seborrheic dermatitis, patients may present with symptoms of one of the following associated conditions: 
- Parkinsonism
- Epilepsy
- Depressive mood disorder
- Traumatic brain injury
- Spinal cord injury
- HIV
- Lymphoma
- Downs syndrome
- Hailey-Hailey Disease
- Diabetes mellitus

# Symptoms
Symptoms of seborrheic dermatitis may be categorized according to age as follows:

## Infants
Infants usually present in the first few months of life. Symptoms can be divided into following types depending on extent of involvement.
- Localized
Redness and flaking
Pruritis
Most common sites involved are scalp and face
Other sites involved include retroauricular area, nasolabial folds, cheeks, eyebrows and eyelids
Napkin or diaper area involvement
- Redness and flaking
- Pruritis
- Most common sites involved are scalp and face
- Other sites involved include retroauricular area, nasolabial folds, cheeks, eyebrows and eyelids
- Napkin or diaper area involvement
- Generalized
Few cases may present with generalized involvement such as lower abdomen, groin and pubic area.
- Few cases may present with generalized involvement such as lower abdomen, groin and pubic area.

## Adults
The most common symptoms of seborrheic dermatitis may be divided into two types based on extent of involvement:
- Localized
Macules, thin plaques, or red patches(scalp, face, nasolabial folds, anterior hairline, eyebrows, glabella region of the forehead, melolabial folds, ears, central chest, and genital region)
Pruritis
Fine scaling (mild cases)
Redness and yellow to white crusting or scaling (severe disease)
Redness, itching and yellow crusting of eye lashes (Blepharitis).
Repeated itching of ear causing secondary bacterial infection resulting in fever and ear pain.
- Macules, thin plaques, or red patches(scalp, face, nasolabial folds, anterior hairline, eyebrows, glabella region of the forehead, melolabial folds, ears, central chest, and genital region)
- Pruritis
- Fine scaling (mild cases)
- Redness and yellow to white crusting or scaling (severe disease)
- Redness, itching and yellow crusting of eye lashes (Blepharitis).
- Repeated itching of ear causing secondary bacterial infection resulting in fever and ear pain.
- Generalized
Patients with HIV or other immunosupressive conditions such as malignancies usually present with more severe disease involving unusual sites such as extremities.
- Patients with HIV or other immunosupressive conditions such as malignancies usually present with more severe disease involving unusual sites such as extremities.

# Physical Examination
Physical examination may be divided into two types according to age group:

## Imaging Findings
There are no imaging findings associated with  seborrheic dermatitis.

## Other Diagnostic Studies
There are no other diagnostic studies for seborrheic dermatitis.

# Treatment
The mainstay of treatment for seborrheic dermatitis is medical therapy. Depending on age and severity of symptoms the treatment may be categorized as follows:
The following are the preferred treatment regimens for seborrheic dermatitis:
- 1. Antifungal agents
- Preferred regimen (1): Ketoconazole 2% in shampoo, foam, gel, or cream
- Scalp: Twice/week for clearance THEN once/week or every other week for maintenance
- Other areas: From bid to twice/week for clearance THEN from twice/week to once every other week for maintenance
- Preferred regimen (2): Bifonazole 1% in shampoo or cream
- Scalp: 3 times/week for clearance
- Other areas: qd for clearance
- Preferred regimen (3): Ciclopirox olamine (also called ciclopirox) 1.0% or 1.5% in shampoo or cream
- Scalp: Twice to 3 times/week for clearance THEN once/week or every 2 week for maintenance
- Other areas: Twice daily for clearance THEN qd for maintenance
- 2. Corticosteroids
- Preferred regimen (1): Hydrocortisone 1% in cream areas other than scalp qd or bid
- Preferred regimen (2): Betamethasone dipropionate 0.05% in lotion scalp and other areas qd or bid
- Preferred regimen (3): Clobetasol 17- butyrate 0.05% in cream areas other than scalp qd or bid
- Preferred regimen (4): Clobetasol dipro- pionate 0.05% in shampoo
- Scalp: Twice weekly in a short- contact fashion (up to 10 min application, then washing)
- Preferred regimen (5): Desonide 0.05% lotion bid on scalp and other areas
- 3. Lithium salts
- Preferred regimen: Lithium succinate AND Zinc sulfate Oin

## Plant-based treatments
The World Health Organization mentions Aloe vera gel as a yet to be scientifically proven traditional medicine treatment for Seborrhoeic dermatitis.
- Arctium lappa (Burdock) oil
- Chelidonium majus (Celandine)
- Glycyrrhiza glabra (Licorice)
- Melaleuca (Tea tree) species
- Plantago (Plantain) species
- Symphytum officinale (Comfrey)
- Zingiber officinale (Ginger) root juicetreatment containing 8% Lithium succinate AND 0.05% Zinc sulfate
- Preferred regimen: Lithium gluconate 8% in gel bid on areas other than scalp

## Surgery
Surgical intervention is not recommended for the management of seborrrheic dermatitis.

## Prevention

### Primary Prevention
There is no established method for prevention of seborrheic dermatitis.

### Secondary Prevention
Secondary prevention strategies following seborrheic dermatitis include:
- Using of 1% ciclopirox shampoo once or twice weekly for 4 weeks. Shampooing once weekly or once every two weeks decreases the relapse rate of seborrheic dermatitis.
- Using 2% ketoconazole such as once a week or twice a week may decrease relapse of seborrheic dermatitis.
- Ketoconazole 2% shampoo may have greater prophylactic effect against relapse than selenium sulfide.