Seborrhoeic dermatitis

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Cradle cap, which is seborrhoeic dermatitis of the infant scalp

Seborrhoeic dermatitis (also spelled seborrheic dermatitis in American English) is a long-term skin disorder.<ref name="Ij2017" /> Symptoms include flaky, scaly, greasy, and occasionally itchy and inflamed skin.<ref name="Mer2019" /><ref name="Bor2019" /> Areas of the skin rich in oil-producing glands are often affected including the scalp, face, and chest.<ref name="Ij2017" /> It can result in social or self-esteem problems.<ref name="Ij2017" /> In babies, when the scalp is primarily involved, it is called cradle cap.<ref name="Mer2019" /> Mild seborrhoeic dermatitis of the scalp may be described in lay terms as dandruff due to the dry, flaky character of the skin.<ref name="BMJ2015" /> However, as dandruff may refer to any dryness or scaling of the scalp, not all dandruff is seborrhoeic dermatitis.<ref name="BMJ2015" /> Seborrhoeic dermatitis is sometimes inaccurately referred to as seborrhoea.<ref name="Ij2017" />

The cause is unclear but believed to involve a number of genetic and environmental factors.<ref name=Mer2019>Template:Cite web</ref><ref name=Ij2017/> Risk factors for seborrhoeic dermatitis include poor immune function, Parkinson's disease, and alcoholic pancreatitis.<ref name=Ij2017/><ref name=BMJ2015/> The condition may worsen with stress or during the winter.<ref name=Ij2017/> Malassezia yeast is believed to play a role.<ref name=BMJ2015>Template:Cite journal</ref> It is not a result of poor hygiene.<ref>Template:Cite web</ref> Diagnosis is typically clinical and based on the symptoms present.<ref name=Ij2017/><ref name=":2" /> The condition is not contagious.<ref>Template:Cite web</ref>

The typical treatment is topical antifungal cream and anti-inflammatory agents.<ref name=Bor2019>Template:Cite journal</ref> Specifically, ketoconazole or ciclopirox are effective.<ref name=Ok2015>Template:Cite journal</ref> Seborrhoeic dermatitis of the scalp is often treated with shampoo preparations of ketoconazole, zinc pyrithione, and selenium.<ref name=":1" />

The condition is common in infants within the first three months of age or adults aged 30 to 70 years.<ref name=Mer2019/><ref name=Ij2017>Template:Cite journal</ref><ref name=Stat2019>Template:Cite book</ref> It tends to affect more males.<ref name=":3">Template:Cite journal</ref> Seborrhoeic dermatitis is more common in African Americans, among immune-compromised individuals, such as those with HIV, and individuals with Parkinson's disease.<ref name=":1" /><ref name=":3" /> Template:TOC limit

Signs and symptoms

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Seborrhoeic dermatitis on upper face/head

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Seborrhoeic dermatitis on the shoulder

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Seborrhoeic dermatitis on eyelids

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Seborrhoeic dermatitis on the eyebrows and scalp

Seborrhoeic dermatitis typically appears as oily, yellowish, flaky skin. Although commonly associated with oily skin, it can also appear on dry scalps or skin, where the flaking may look similar to dandruff. The flakes can be fine, loose, and diffuse or thick and adherent.<ref name=":1">Template:Cite book</ref><ref name=":2">Template:Cite book</ref> In addition to flaky skin, seborrhoeic dermatitis can have areas of red, rashy, inflamed, and itchy skin that coincide with the area of skin flaking, but not all individuals have this symptom.<ref name=":2" />

Seborrhoeic dermatitis of the scalp can appear similarly to dandruff.<ref name=":1" /> When the scalp is affected, there can be associated temporary hair loss.<ref name=":1" /> Such hair loss varies in appearance from diffuse thinning to patchy areas of hair loss.<ref name=":1" /> On close inspection, the locations where hair has thinned may have broken stubs of hair and pustules around the hair follicles.<ref name=":1" /> Individuals with more pigmented skin tones may experience increased or decreased skin pigmentation in affected areas.<ref name=":3" />

Various locations can be affected by seborrhoeic dermatitis. Commonly affected areas include the face, ears, scalp, and across the body. It is less common in intertriginous areas, which are areas where the skin folds and comes into contact with itself, such as the groin or the underarms.<ref name=":1" />

Seborrhoeic dermatitis' symptoms are typically mild and appear gradually but are often persistent, lasting weeks to years.<ref name=":2" /><ref name=":1" /><ref name="merckmanuals">Template:Cite web</ref> Individuals with seborrhoeic dermatitis are subject to recurrent bouts and it may be a lifelong condition.<ref name=":2" /> Seborrhoeic dermatitis can also occur quickly and severely in patients with Human Immunodeficiency Virus (HIV). This is sometimes the first indication of HIV.<ref name=":3" />

Causes

The cause of seborrhoeic dermatitis has not been fully clarified as of 2019.<ref name=Des2013>Template:Cite journal</ref><ref name="pmid31310695">Template:Cite journal</ref>

In addition to the presence of Malassezia, genetic, environmental, hormonal, and immune-system factors are necessary for and/or modulate the expression of seborrhoeic dermatitis.<ref name=pmid10821151>Template:Cite journal</ref><ref>Template:Cite journal</ref> The condition may be aggravated by illness, psychological stress, fatigue, sleep deprivation, change of season, and reduced general health.<ref name="aafp" />

Fungi

The condition is thought to be due to a local inflammatory response to overgrowth by Malassezia fungi species in sebum-producing skin areas including the scalp, face, chest, back, underarms, and groin.<ref name="Bor2019" /><ref name="pmid31310695" /> This is based on observations of high counts of Malassezia species in skin affected by seborrhoeic dermatitis and on the effectiveness of antifungals in treating the condition.<ref name="pmid31310695" /> Species of Malassezia implicated in Seborrhoeic dermatitis include M. furfur (formerly Pityrosporum ovale), M. globosa, M. restricta, M. sympodialis, and M. slooffiae.<ref name="Bor2019" />

Malassezia appears to be a significant factor in seborrhoeic dermatitis, but it is thought that other factors are necessary for the presence of Malassezia to result in seborrhoeic dermatitis.<ref name="pmid31310695" /> For example, summer growth of Malassezia in the skin alone does not result in seborrhoeic dermatitis.<ref name="pmid31310695" /> Besides antifungals, the effectiveness of anti-inflammatory drugs, which reduce inflammation, and antiandrogens, which reduce sebum production, provide further insights into the pathophysiology of seborrhoeic dermatitis.<ref name="Bor2019" /><ref name="TrivediShinkai2017">Template:Cite journal</ref><ref name="ParadisiFabbri2010">Template:Cite journal</ref>

Bacteria

Several bacteria, including Propionibacterium species and Staphylococcus aureus, have been shown to have some level of interaction with seborrhoeic dermatitis, though their exact impact is not known.<ref name=":4">Template:Cite journal</ref><ref name=":3" />

Nutrition

Seborrhoeic dermatitis-like eruptions are also associated with pyridoxine (vitamin B₆) and riboflavin (vitamin B₂) deficiency.<ref>Template:Cite book</ref><ref name=":2" /> In children and babies, issues with Δ⁶-desaturase enzymes<ref name="aafp">Template:Cite journal</ref> have been correlated with increased risk.

Immune dysfunction

Those with immunodeficiency (especially infection with HIV) and with neurological disorders that may impact immune system function such as Parkinson's disease (for which the condition is an autonomic sign) and stroke are particularly prone to it.<ref>Template:Cite web</ref>Template:Unreliable medical source

Climate

Climate can affect seborrheic dermatitis, but there is a lack of consensus about which climates tend to exacerbate seborrheic dermatitis the most. Some studies show low humidity and low temperature are responsible for the high frequency of seborrheic dermatitis.<ref>Template:Cite journal</ref> Others suggest hot environments may also worsen seborrhoeic dermatitis.<ref name=":3" /> Yet another described that high humidity and low UV exposure are culpable.<ref name=":5">Template:Cite journal</ref> Dry skin and an impaired skin barrier contribute to the condition.<ref name=":3" /><ref name=":4" /> It is likely that climate and weather variations affect the water and lipid content of skin.<ref name=":4" />

Mechanism

Seborrhoeic dermatitis is a complex condition with many interacting factors that are not yet fully explained.<ref name="pmid31310695" /> In general, the major factors that influence the development and severity include Malassezia yeast present on and in the skin, skin production of oily sebum, and a subsequent inflammatory response against Malassezia and their byproducts.<ref name=":3" /> Additional factors involved in the condition are a compromised skin barrier, the makeup and amount of sebum produced, the character of the immune response and inflammation, and the presence of other microbe species inhabiting the skin.<ref name="pmid31310695" /><ref name=":3" />

A suggested series of events leading to seborrhoeic dermatitis is an initially damaged skin barrier and abnormal sebum production, which leads to a change in the microbiome of the skin that in turn elicits an immune response.<ref name="pmid31310695" /> An alternative explanation is an increase in sebum production feeding an increase in the Malassezia population that instigates inflammation; the inflammation then causes cellular changes that damage the skin barrier. This barrier disruption then encourages additional Malassezia growth and inflammation and again worsens skin barrier function.<ref name=":3" />

Diagnosis

Typically, seborrhoeic dermatitis is a clinical diagnosis based on a physician's expertise in identifying and differentiating skin conditions based on the history of the individual and the appearance of the skin.<ref name=":2" /> However, seborrhoeic dermatitis may also be diagnosed with additional testing. The least invasive test is a visual inspection in the clinic using a Wood's Lamp.<ref name=":1" /> A KOH test can also be used, where skin scraping of the affected skin may also be taken and prepared with potassium hydroxide (KOH) and visualized under a microscope to look for Malassezia or other microbiological cells. Additionally, a fungal culture of the affected skin may be taken to attempt to grow and identify the causative organism.<ref name=":1" />

Differential diagnosis

Seborrhoeic dermatitis can look similar to other skin conditions that share its characteristic dry, flaky, scaly, and inflamed appearance, but have different causes and treatments. Physicians use the history of the individual with the skin condition as well as other tests to identify which disorder is present. Other conditions that may be confused with seborrhoeic dermatitis based on appearance are listed below.<ref name=":2" /><ref name=":1" />

• Atopic dermatitis (eczema)<ref name=":1" />
• Contact dermatitis<ref name=":2" />
• Psoriasis<ref name=":1" />
• Tinea capitis and tinea corporis<ref name=":2" />
• Candidiasis<ref name=":3" />
• Tinea versicolor<ref name=":2" />
• Pityriasis rosea<ref name=":2" />
• Impetigo<ref name=":3" />
• Drug reaction<ref name=":3" />
• Cutaneous T-Cell Lymphoma<ref name=":1" />

Management

Medications

A variety of different types of medications can reduce symptoms of seborrhoeic dermatitis.<ref name=Bor2019/> These include certain antifungals, anti-inflammatory agents like corticosteroids and nonsteroidal anti-inflammatory drugs, antiandrogens, and antihistamines, among others.<ref name=Bor2019/><ref name=Des2013 /> Treatments must take into consideration potential side effects, especially with long-term use given the chronic nature of seborrhoeic dermatitis.Template:POV statement Initial therapy is usually a topical preparation with an agreeable side effect profile.<ref name=":3" />

Antifungals

Regular use of an over-the-counter or prescription antifungal shampoo or cream is a common treatment. The topical antifungal medications ketoconazole and ciclopirox have the best evidence.<ref name="Ok2015" /> Ketoconazole should be used twice per week.<ref name=":2" /> Shampoo or soap containing zinc pyrithione or selenium disulfide is also used.<ref name=":2" /> These options should be used daily but may also be used in conjunction with a ketoconazole shampoo regimen on alternate days.<ref name=":2" /> It is unclear if other antifungals are equally effective, as this has not been sufficiently studied.<ref name="Ok2015" /> Antifungals that have been studied and found to be effective in the treatment of seborrhoeic dermatitis include ketoconazole, fluconazole, miconazole, bifonazole, sertaconazole, clotrimazole, flutrimazole, ciclopirox, terbinafine, butenafine, selenium disulfide, and lithium salts such as lithium gluconate and lithium succinate.<ref name="Ok2015" /><ref name=Bor2019/>

Topical climbazole appears to have little effectiveness in the treatment of seborrhoeic dermatitis.<ref name="Ok2015" /> Systemic therapy with oral antifungals including itraconazole, fluconazole, ketoconazole is effective, but adverse side effects have been documented for fluconazole and ketoconazole, with the latter not recommended for use, while itraconazole, with its good safety profile, is the most commonly prescribed.<ref name="Bor2019" /> Terbinafine is said to be effective, but with adverse side effects, while other sources state it is not effective and should not be used.<ref name="Bor2019" /><ref name=":1" />

Anti-inflammatory treatments

Topical corticosteroids are effective in short-term treatment of seborrhoeic dermatitis and are as effective or more effective than antifungal treatment with azoles. These are sometimes used for only a few weeks at a time.<ref name=":1" />Template:Additional citation needed There is also evidence for the effectiveness of topical calcineurin inhibitors like tacrolimus and pimecrolimus as well as lithium salt therapy.<ref>Template:Cite journal</ref> Calcineurin inhibitors were also effective in reducing the growth of Malassezia, offering two routes by which they may treat seborrhoeic dermatitis.<ref name=":5" /> Medications such as calcineurin inhibitors should not be used in individuals with seborrhoeic dermatitis who are immune-compromised because they cause further immune suppression.<ref name=":1" />

Oral immunosuppressive treatment, such as with prednisone, has been used in short courses for seborrhoeic dermatitis, as a last resort due to its potential side effects.<ref name="oral treatments"/>

Antihistamines

Antihistamines are used primarily to reduce itching, if present. However, research studies suggest that some antihistamines have anti-inflammatory properties.<ref>Template:Cite journal</ref>

Keratolytics

Keratolytics help the skin via exfoliation of built-up skin flakes and thereby remove scale. They are applied topically to the affected area. Keratolytics include urea, salicylic acid, coal tar, lactic acid, pyrithione zinc and propylene glycol.<ref name=":5" /> Coal tar shampoo formulations can be effective.<ref name=":2" /><ref name=":5" /> Although no significant increased risk of cancer in human treatment with coal tar shampoos have been found, caution is advised since coal tar is carcinogenic in animals, and heavy human occupational exposures do increase cancer risks.<ref>Template:Cite journal</ref>

Other treatments

• Isotretinoin, a sebosuppressive agent, may be used to reduce sebaceous gland activity as a last resort in refractory disease.<ref name=":0">Template:Cite journal</ref> However, isotretinoin has potentially serious side effects, and few patients with seborrhoeic dermatitis are appropriate candidates for therapy.<ref name="oral treatments">Template:Cite journal</ref>
• Topical 0.75% and 1% Metronidazole<ref name="Ok2015" /><ref name=":1" />
• Topical 4% nicotinamide<ref name=Bor2019/>
• Topical sulfacetamide<ref name=":1" />
• Tea tree oil<ref name=":3" />
• Cannabidiol shampoo<ref name=":5" />
• Frequent washing to avoid the build-up of scale, especially on the scalp, but while avoiding overly drying the skin<ref name=":3" /><ref name=":1" /><ref name=":4" />
• Avoiding damaging skin with harsh grooming or chemical irritants<ref name=":4" />
• Bicalutamide, an antiandrogen, has been observed in one patient to have potentially been the cause of seborrheic dermatitis relief. However, even if it were demonstrated that bicalutamide or any other antiandrogen is a treatment, it is not recommended due to side effects and price.<ref name="AR2020">Template:Cite web</ref>

Phototherapy

Template:See also Another option is natural and artificial UV radiation since it can inhibit the growth of Malassezia yeast.<ref name="the effect of UV-light-ADV">Template:Cite journal</ref> Some recommend photodynamic therapy using UV-A and UV-B laser or red and blue LED light to inhibit the growth of Malassezia fungus and reduce seborrhoeic inflammation.<ref name="the effect of UV-light-ADV" /><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Outcome

Seborrhoeic dermatitis is generally a chronic and recurring condition. Individuals may have the condition for several weeks to months, but it may also last years or their lifetime. There may be periods of relapse and worsening.<ref name=":1" /><ref name=":2" />

Epidemiology

Seborrhoeic dermatitis affects 1 to 5% of the general population.<ref name=Des2013 /><ref name="GoldsteinGoldstein2009">Template:Cite book</ref><ref name="FarageMiller2009">Template:Cite book</ref> It is slightly more common in men, but affected women tend to have more severe symptoms.<ref name="FarageMiller2009" /> The condition usually recurs throughout a person's lifetime.<ref name="Jacknin2001" /> Seborrhoeic dermatitis can occur in any age group<ref name="Jacknin2001">Template:Cite book</ref> but often occurs during the first three months of life then again at puberty and peaks in incidence at around 40 years of age.<ref name="pmid24689165">Template:Cite journal</ref><ref name=":4" /> It can reportedly affect as many as 31% of older people.<ref name="FarageMiller2009" /> Infants may also have this condition, though it is typically milder, and is referred to as cradle cap.<ref name=":3" /> Seborrhoeic dermatitis is more common in African-Americans.<ref name=":3" />

Severity is worse in dry climates<ref name="Jacknin2001" /> as well as hot weather, as dry skin can exacerbate the condition.<ref name=":3" /> COVID-19 related mask usage may also cause or exacerbate facial seborrhoeic dermatitis.<ref name=":3" />

Individuals who are immunocompromised have an increased risk of seborrhoeic dermatitis.<ref name=":3" /> Conditions that are associated with increased rates of seborrhoeic dermatitis include individuals with HIV, Hepatitis C, alcoholic pancreatitis, Parkinson's disease, and alcohol abuse.<ref name=":3" /> Seborrhoeic dermatitis is common in people with alcoholism, between 7 and 11 percent, which is twice the normal expected occurrence.<ref>Template:Cite journal</ref>