Is seborrheic dermatitis bacterial or fungal?

Quick Answer

Seborrheic dermatitis is primarily caused by an overgrowth of yeast, specifically Malassezia yeast. While bacteria are not the primary cause, an overabundance of bacteria can exacerbate seborrheic dermatitis symptoms. So seborrheic dermatitis has both fungal and secondary bacterial components.

What Causes Seborrheic Dermatitis?

Seborrheic dermatitis is a common skin condition that mainly affects the scalp, causing scaly, flaky skin and stubborn dandruff. It can also affect other oil-rich areas like the face, upper chest, etc. The exact cause is unknown but it appears to be related to overgrowth of a yeast called Malassezia that is naturally found on the skin’s surface.

Specifically, the Malassezia yeasts feed on oils secreted by the sebaceous glands in the skin. When oil secretion increases, the yeasts multiply rapidly, causing inflammation and the flaky, itchy rash characteristic of seborrheic dermatitis.

So seborrheic dermatitis is primarily caused by fungal overgrowth, not bacteria. However, many people with seborrheic dermatitis also have an overabundance of bacteria on their skin (especially Propionibacteria and Staphylococci species). This bacterial overgrowth can worsen seborrheic dermatitis symptoms.

Key Facts on Seborrheic Dermatitis Causes:

  • Main trigger is overgrowth of Malassezia yeast on the skin’s surface
  • Malassezia yeasts feed on skin oils and proliferate rapidly when oil secretion increases
  • The inflammation caused by the excessive yeasts leads to the characteristic rash and symptoms
  • Bacterial overgrowth (of Propionibacteria and Staphylococci species) is secondary but can worsen symptoms

Evidence That Malassezia Yeast Causes Seborrheic Dermatitis

There are several key pieces of evidence that implicate Malassezia yeast overgrowth as the primary cause of seborrheic dermatitis:

High Density of Malassezia Yeasts in Affected Skin

Studies consistently show much higher population densities of Malassezia yeasts in skin lesions affected by seborrheic dermatitis compared to normal skin. The density can be up to 10 times higher.

Antifungal Treatments Improve Symptoms

Standard treatments for seborrheic dermatitis include topical antifungal creams/shampoos containing ketoconazole, ciclopirox or zinc pyrithione. These treatments aim to reduce Malassezia overgrowth and are often effective at improving seborrheic dermatitis symptoms.

Malassezia Metabolites Irritate Skin

Byproducts from Malassezia yeast metabolism, such as oleic acid, appear to irritate skin and trigger inflammation. Oleic acid levels are higher in skin affected by seborrheic dermatitis.

Aggravating Factors Promote Malassezia Growth

Seborrheic dermatitis flares are associated with factors like stress, fatigue, weather changes and oily skin – all of which can increase sebum/oil production that feeds Malassezia overgrowth.

Malassezia Identified in Affected Skin Lesions

Using techniques like skin scrapings and tape strips, studies consistently isolate and culture Malassezia yeasts from seborrheic dermatitis lesions at much higher rates than normal skin. This demonstrates a link between Malassezia and seborrheic dermatitis.

Bacteria May Play a Secondary Role

Although Malassezia overgrowth appears the central cause, bacterial overgrowth can exacerbate seborrheic dermatitis in some individuals. Two main bacteria associated are:

Propionibacteria

Skin areas affected by seborrheic dermatitis often show overgrowth of Propionibacteria species like P. acnes. Propionibacteria feed on sebum, produce inflammatory compounds and can worsen seborrheic dermatitis inflammation.

Staphylococci

Some studies note higher rates of Staphylococcus epidermidis bacteria in seborrheic dermatitis lesions. Staphylococci may intensify inflammation. However, rates much lower compared to Malassezia yeasts.

So bacterial overgrowth is secondary, but potentially still relevant. Combination antifungal + antibiotic treatment is sometimes used to cover all bases. But antifungals remain the cornerstone.

Summarizing the Fungal vs Bacterial Role

In summary:

  • Overgrowth of Malassezia yeast is the central, underlying trigger of seborrheic dermatitis.
  • Yeast feed on sebum, multiply rapidly, and irritate/inflame skin.
  • Bacteria like Propionibacteria and Staphylococci may play a secondary role by worsening inflammation in some cases.
  • Therefore seborrheic dermatitis has a primary fungal cause with secondary bacterial involvement.

Typical Symptoms of Seborrheic Dermatitis

Seborrheic dermatitis most often affects the scalp, causing stubborn dandruff and scalp flaking. Other common symptoms include:

Scalp Symptoms

  • Flaky, white or yellowish scales or crust on the scalp
  • Dandruff and itchiness
  • Red, inflamed skin under scales
  • Greasy appearance along hairline
  • Mild to intense itching

Facial Symptoms

  • Red, greasy patches on skin folds around nose, eyebrows, ears, etc.
  • Flaking, yellowish scales on face, ears and scalp
  • Itching, burning or stinging

Other Body Areas

  • Flaky, scaly patches in chest area, groin, underarms, etc.
  • May affect skin behind ears, neck, shoulders, breast
  • Mild to intense itchiness

Symptoms range from mild dandruff to severe inflammation and flaking. They tend to come and go in flare-ups triggered by stress, fatigue, weather changes, and skin irritation.

Who Gets Seborrheic Dermatitis?

Seborrheic dermatitis can affect people of all ages. However, it most commonly occurs in:

  • Infants within first 3-6 months of life (infantile seborrheic dermatitis)
  • Adolescents and adults between ages 30-60 years

Up to 5% of the general population develops seborrheic dermatitis. People with certain medical conditions have an increased risk:

  • Parkinson’s disease – Very high risk of seborrheic dermatitis on scalp and face
  • HIV/AIDS – Increased risk of severe seborrheic dermatitis
  • Other conditions – Multiple sclerosis, depression, epilepsy, stroke, spinal injury

In infants, seborrheic dermatitis usually resolves on its own within the first year. But adolescents and adults often experience recurrent episodes without preventive treatment.

Body Areas Affected by Seborrheic Dermatitis

Seborrheic dermatitis can affect several areas of the body where oil glands are most active. The main body areas are:

Scalp

The scalp is the most common site of seborrheic dermatitis due to the high density of oil glands that line hair follicles. It often manifests as stubborn dandruff, scalp flaking and itchiness.

Face

Facial areas rich in oil glands are also prone to seborrheic dermatitis, especially the eyebrows, nasolabial folds around mouth and nose, eyelids, forehead and beard area.

Upper Chest and Back

The upper chest and back can develop seborrheic dermatitis. Symptoms appear as flaky, scaly patches and redness in the skin folds and creases.

Other Sites

Less common sites include behind the ears, the groin area, armpits and skin folds under breasts or stomach. Basically anywhere with oil gland activity may be affected.

Diagnosing Seborrheic Dermatitis

Doctors can often diagnose seborrheic dermatitis simply by examining the distinctive rash and scaly patches. Other techniques to confirm diagnosis include:

Skin Scraping

A skin scraping from affected areas can be examined under the microscope. This allows identification of Malassezia yeasts and bacteria.

Skin Culture Test

Culturing skin scrapings on special media can isolate and identify Malassezia yeasts from seborrheic dermatitis lesions.

Tape Stripping

Applying and removing adhesive tapes from affected skin picks up yeasts and bacteria for identification.

Skin Biopsy

A skin biopsy may help rule out conditions like psoriasis. Biopsies show inflammation and Malassezia overgrowth.

Doctors also assess if the person has any underlying medical conditions associated with increased risk of this fungal skin disorder.

Seborrheic Dermatitis vs Dandruff

Dandruff and seborrheic dermatitis can be confusing – but they differ in severity and cause:

Seborrheic Dermatitis

  • Scaly, crusty flakes on scalp, face, chest
  • Red, greasy skin with visible inflammation
  • Often accompanied by itchiness or soreness
  • Due to Malassezia yeast overgrowth
  • Lasts more than 2-4 weeks if untreated

Dandruff

  • Flaking but more dry, powdery scales
  • Mild or no redness/inflammation
  • Little to no itching
  • Caused by dry skin, irritation, skin fungi
  • Usually self-resolves within 2-4 weeks

So seborrheic dermatitis involves more intense, stubborn inflammation and scaling not seen with mild dandruff flares.

Seborrheic Dermatitis Treatment Guidelines

Doctors often recommend a multi-step approach for treating seborrheic dermatitis:

Antifungal Shampoos and Creams

Reducing Malassezia overgrowth is key, so topical antifungals like ketoconazole shampoo or ciclopirox cream applied daily to affected areas.

Medicated Shampoos

Coal tar, salicylic acid or selenium sulfide shampoos help reduce scaling, inflammation and itch. Rotate different shampoo types.

Topical Corticosteroids

For moderate to severe cases, doctors may prescribe short-term, topical steroid lotion/creams to control inflammation.

Oral Antifungals

For severe seborrheic dermatitis cases, oral antifungals like fluconazole or itraconazole may be used short-term.

Phototherapy

For severe, resistant cases UVB or PUVA phototherapy may be used to reduce yeast counts and inflammation.

With the above treatments, most cases of seborrheic dermatitis can be effectively managed. But lifelong treatment and flare prevention are often required.

Home Remedies for Seborrheic Dermatitis

Alongside medical treatment, people can try these natural remedies to help control seborrheic dermatitis:

Apple Cider Vinegar

The apple cider vinegars antifungal and anti-inflammatory properties may reduce yeast overgrowth and skin inflammation.

Tea Tree Oil

Tea tree oil contains terpinen-4-ol that acts as an antifungal against Malassezia. It may help reduce yeast overgrowth when applied to affected skin.

Aloe Vera Gel

Aloe vera gel has anti-inflammatory, antimicrobial and wound healing properties. It may aid healing of seborrheic dermatitis lesions.

Probiotics

Oral probiotics aim to restore balance between yeast and bacteria on the skin and scalp, preventing overgrowth.

Natural Oils

Some natural oils like MCT oil, evening primrose and borage oil help moisturize and reduce inflammation associated with seborrheic dermatitis when applied topically.

Seborrheic Dermatitis Prevention Tips

To prevent seborrheic dermatitis flares try:

  • Use antifungal shampoo (ketoconazole, zinc) 2-3x weekly to prevent yeast overgrowth on scalp
  • Avoid heavy oils and creamy products that may promote Malassezia growth
  • Manage oil production by washing face AM/PM with gentle cleanser
  • Avoid skin irritants like harsh soaps, fragrances, dyes
  • Reduce stress through relaxation techniques
  • Get regular exercise and sleep to boost immune defenses

Quickly treating flares also prevents spreading and worsening of seborrheic dermatitis lesions. See a dermatologist at first signs of symptoms.

Takeaway Points

  • Seborrheic dermatitis is primarily caused by overgrowth of Malassezia yeast on the skin’s surface.
  • Secondary bacterial overgrowth of Propionibacteria and Staphylococci may worsen inflammation.
  • Topical antifungal treatments reduce Malassezia overgrowth and improve seborrheic dermatitis symptoms.
  • With treatment and prevention strategies, seborrheic dermatitis can be well-controlled in most cases.

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