Scalp microbiome: how it influences hair loss and alopecia

The scalp microbiome has become one of the most studied factors in modern dermatology and trichology. Its impact on hair loss , androgenetic alopecia , seborrheic dermatitis , and hair follicle health is much greater than previously thought.

Understanding how the hair microbiota works allows us to prevent inflammation, modulate pathologies, and improve hair quality.

What is the scalp microbiota and why does it affect hair growth?

The scalp microbiota is the collection of bacteria, fungi, and microorganisms that live on the skin and within the hair follicle.

The microbiome , for its part, refers to the genes and metabolites of these microorganisms.

A balanced microbiota protects the scalp, while dysbiosis can trigger:

• chronic inflammation

• hair loss

• seborrheic dermatitis

• folliculitis

• acceleration of androgenetic alopecia

  
  

That's why studying the hair microbiome has become essential in modern hair medicine.

Surface microbiome vs. follicular microbiome: two ecosystems that control hair health

Surface microbiome of the scalp

The outermost layer is dominated by aerobic flora such as:

• Cutibacterium acnes

• Staphylococcus epidermidis

• Malassezia globosa and Malassezia restricta

  
  

This microbiome regulates pH, sebum, the skin barrier, and the immune response.

An imbalance promotes seborrheic dermatitis , dandruff, and increased hair loss.

Hair follicle microbiome

Deeper, more stable, and with anaerobic flora. It directly influences the hair cycle , perifollicular inflammation, and pathologies such as:

• scarring alopecias

• folliculitis decalvans

• androgenetic alopecia (modulated by chronic inflammation)

  
  

The link between follicular microbiome and subclinical inflammation that accelerates follicle miniaturization is currently being investigated here.

How scalp dysbiosis causes hair loss

1. Seborrheic dermatitis and dandruff

Malassezia overgrowth is one of the most frequent imbalances.

• increased inflammation

• produces irritating metabolites

• weakens the follicle

• reactive telogen effluvium

• worsens hair quality

  
  

2. Folliculitis and inflammatory outbreaks

An imbalance between Cutibacterium acnes , S. aureus , and S. epidermidis leads to:

• pustules

• scalp pain

• localized inflammatory drop

• risk of scarring alopecia if left untreated

  
  

3. Folliculitis decalvans: a scarring alopecia influenced by the microbiome

The latest scientific evidence shows that interaction with Staphylococcus aureus triggers:

• aggressive neutrophilic phase

• follicular destruction

• chronic lymphocytic phase

• irreversible hair loss

4. Microbiome and androgenetic alopecia (AGA)

Although AGA is genetic and hormonal, it is now known that dysbiosis can accelerate miniaturization .

Key factors:

• Malassezia increases perifollicular inflammation

• Cutibacterium acnes produces proinflammatory porphyrins

• Dense biofilms impede follicular oxygenation

• Chronic inflammation → apoptosis and blockage of Wnt pathways

  
  

The gut microbiome and its relationship to hair loss

Intestinal dysbiosis can alter:

• systemic immunity

• widespread inflammation

• hormonal metabolism

• resistance to treatments

How to improve the scalp microbiome

1. Proper hair hygiene

Contrary to the myth, many patients who wash their hair once a week develop dense biofilms and dysbiosis.

General recommendation: frequent washing adapted to the type of sebum

2. Maintain acidic pH

A pH between 4.5–5.5 promotes microbial balance and protects the hair shaft.

3. Reduce damage to the cuticle

Heat, dyes, and UV light alter the hair structure and the microenvironment of the hair shaft microbiome.

4. Ingredients with growing evidence

• antioxidants

• bacterial ferments

• mild anti-Malassezia actives

• topical prebiotics

• sebum-regulating shampoos

Conclusion: The microbiome is key to hair health and hair loss treatment

The scalp microbiome directly influences inflammation, hair loss, hair follicle quality, and the progression of various types of alopecia. Optimizing it is not only a scientific strategy but also an effective tool for improving treatments and aesthetic outcomes.

There is no hair health without a balanced microbiome.

Microbioma y salud capilar