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Pathology of Folliculitis  

Dr Sampurna Roy MD          





Folliculitis is an inflammatory process distributed around hair follicles and involving follicular opening or adjacent perifollicular skin. 

Patients with depressed immune system, diabetes mellitus and obesity have a greater risk of contracting folliculitis.

Common sites for folliculitis are scalp, face, thigh, legs and buttock.


I  Infectious-  

Superficial- (usually suppurative)- Bacteria, fungus, syphilis, virus.

Deep- (usually granulomatous)- Fungi or bacteria

II Non infectious-

Superficial- (usually suppurative)-  Acne vulgaris, rosacea, follicular mucinosis, steroid induced.

Deep- (usually granulomatous)-  Acne vulgaris- conglobata & keloidal forms and perforating form.

Deep- (scarring) folliculitides- Folliculitis decalvans ; Folliculitis keloidalis nuchae.

Spongiotic- Fox fordyce disease, atopic dermatitis, pruritic folliculitis of pregnancy.

III Perifolliculitis-

Predominantly lymphocytic- Lichen planopilaris, pityriasis rubra pilaris.

Predominantly granulomatous-  Rosacea,  dermatitis perioralis.


Infectious Folliculitis  (Infectious Disease Online)

Histopathological patterns in cutaneous infection

The most common cause of folliculitis is infection by bacteria, staphylococcus aureus.

Other infective folliculitis include Pseudomonas folliculitis (hot-tub folliculitis).

This is characterised by dense collection of polymorphs in pilar canal and prominent perifollicular lymphocytic infiltration.

Gram (-) folliculitis caused by Klebsiella or Enterobacter (usually around nose), Pityrosporum folliculitis, tinea capitis and tinea barbae causing folliculitis (fungal infection caused by candidial species and dermatophytes).

Eosinophilic pustular folliculitis is usually seen in HIV positive patients.

Herpetic folliculitis caused by Herpes simplex virus may produce vesicles and pustules in the beard area of men.  


Folliculitis in a case of dermatophyte infection   


Further reading:

Infectious folliculitis and dermatophytosis.

Pseudomonas folliculitis in Arabian baths.

Malassezia folliculitis in an infant.

Microbiology of folliculitis: a histological study of 39 cases.

Histopathological study of cutaneous manifestations in HIV and AIDS patients.

Successful treatment of recalcitrant folliculitis barbae and pseudofolliculitis barbae with photodynamic therapy.

Necrotizing herpes folliculitis. Report of one case.   


Rosacea:  Visit: Pathology of Rosacea

Syn: Acne Rosacea 

Affects mainly center and sides of the face.

Grade I-   Erythematous telangiectatic

Grade II-  Papular /papulopustular

Grade III- Nodular/plaque

There is sebaceous hyperplasia & periadnexal inflammation.

In some cases granulomatous infiltrate is present.

Intact or fragmented Demodex is sometimes present.


Microscopic images of Rosacea


Acne Vulgaris:

Occurs mostly during adolescence.

Usual sites are face and upper half of trunk.

The lesion presents as :

Grade I   Comedones-

Black heads (open follicles) 

White heads (closed follicles)

Grade II  Papulopustules-

Grade III Nodulocystic (conglobata)-

The ruptured pilosebaceous unit is surrounded by neutrophils.

There is foreign body (granulomatous) reaction to the follicular contents.

If collection of polymorphs is small and superficial a pustule results.

If the collection is large and deep a nodule forms.

Further reading

Pathophysiology of acne. What is confirmed? .

Skin microbiota: overview and role in the skin diseases acne vulgaris and rosacea.

Sonography of acne vulgaris.

Association of HSD17B3 and HSD3B1 polymorphisms with acne vulgaris in Southwestern Han Chinese.






Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)

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