Gram-negative folliculitis

Author: Dr Amanda Oakley Dermatologist, Hamilton, New Zealand, 1999. Reviewed and updated by Vanessa Ngan, Staff Writer; Copy Editor: Clare Morrison, April 2014.

What is Gram-negative folliculitis?

Gram-negative folliculitis is an acne-like disorder caused by a bacterial infection. Gram-negative bacteria include Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Klebsiella and Proteus species.

The term "Gram negative" refers to the staining pattern of the organisms in the laboratory. Certain bacteria do not take up a stain known as "Gram".

Gram-negative folliculitis may result from long-term treatment of acne with tetracycline or topical antibiotics.

Other skin conditions due to Gram-negative bacteria include:

What does Gram-negative folliculitis look like?

Gram-negative folliculitis is a pustular rash resembling acne. It is often mistaken as a worsening of acne as it usually occurs in patients with existing acne.

In about 80% of patients, Gram-negative folliculitis causes superficial pustules with relatively few papules and comedones. These lesions are usually caused by Klebsiella, Escherichia and Serratia species.

In about 20% of patients with Gram-negative folliculitis, lesions are deep, nodular and cyst-like. These are caused by Proteus species, which are able to invade deeply into the skin and create pus-filled abscesses and cysts.

Gram-negative folliculitis lesions are usually found around the area of the upper lip under the nose, to the chin and cheeks.

How is the diagnosis of Gram-negative folliculitis made?

Poor response of a pustular rash to usual anti-acne antibiotics may give rise to suspicion that an unusual organism may be present. The diagnosis of Gram-negative folliculitis is made by microscopy / cytology. The bacteria appear red or pink with Gram stain.

Bacterial culture identifies which species is responsible for the infection. The bacteria are tested for antibiotic sensitivity, as this differs among them.

What is the treatment for Gram-negative folliculitis?

Gram-negative folliculitis usually clears promptly with:

Spa-pool folliculitis usually clears within a few days without treatment.

Related information

Email Newsletter

Would you like to receive our dermatology updates by email?


Submit your images

We're seeking high-quality photos of skin diseases.  


Machine diagnosis

Watch DermNet's proposal to create a 'Skin Disease Image Recognition Tool' - winner of the 2017 'Clinicians' Challenge Active Award' by the NZ Ministry of Health and HiNZ.

Subscribe to our mailing list

* indicates required
DermNet NZ Newsletter