Dr. Lauren Livelo 07 Jun 2022

The human skin is normally colonized by some bacteria, fungi, and viruses, which are usually harmless and nontoxic. However, in some cases, these organisms can become pathogenic when there is a breach in the skin barrier and can cause bacterial infections. Bacteria can invade by entering through small breaks in the skin or in the hair follicles. These infections can range from mild to life-threatening conditions; therefore, it is best to consult a physician when a bacterial infection is suspected.

There is a wide variety of bacterial infections diagnosed worldwide. This article will focus on the most common bacterial infections affecting the skin and the underlying soft tissues.


Impetigo can present in two clinical forms: the non-bullous and the bullous type. Impetigo is a common superficial bacterial infection that is usually characterized by the presence of vesicles (fluid-filled small blisters) and/or pustules (pus-filled lesions) that rupture and form honey-colored crusted papules and plaques. This is typical for the non-bullous type of impetigo. Bullous impetigo, on the other hand, initially presents as vesicles and bullae (larger blisters) that rupture and combine to form plaques with honey-colored crusts. Sometimes, there can be accompanying systemic symptoms such as fever, swollen lymph nodes, or body weakness.

Impetigo is typically caused by the bacteria Staphylococcus aureus and Streptococcus pyogenes (Group A beta-hemolytic streptococci/ GABHS), and is spread by direct contact. It is usually found on the face or extremities, but it can affect any part of the body. It is most common in young children, but the adult population can also be affected. Risk factors include:

  • Immunosuppression
  • Having other skin conditions such as atopic dermatitis or contact dermatitis
  • Poor hygiene
  • Trauma to the skin such as insect bites, wounds, burns, lacerations
  • Warm and humid weather
  • Congested and crowded environment

Bacterial Folliculitis

Folliculitis refers to inflammation that begins within the hair follicle, and is caused by a bacterial infection (usually Staphylococcus aureus). It can affect anyone at any age. It presents as small, dome-shaped pustules with redness and some swelling that occur at the opening of a hair follicle. These lesions can be painful and may scar upon healing. The armpits, extremities, and buttocks are the common areas affected, but it can appear on any of the hair-bearing areas of the body such as the head, neck, and trunk. Systemic symptoms are usually absent.

“Hot tub folliculitis” is caused by Pseudomonas aeruginosa. One can be affected after having contact with contaminated water in a hot tub, waterslide, or whirlpool. Mild fever and body weakness may occur.

Furuncles And Carbuncles

Furuncles and carbuncles are deeper infections of the hair follicles. Furuncles, or more commonly called as boils, initially appear as deep-seated red, hard, and tender nodules that develop around a hair follicle. It eventually increases in size and becomes fluctuant and painful. There can be one or several furuncles (Furunculosis) which typically arise in hair-bearing areas such as the neck, face, armpits, and buttocks.

When furuncles coalesce, they form a carbuncle, defined as a collection of infected hair follicles that form deep, swollen, red, and painful masses that can be accompanied by systemic symptoms such as fever and body weakness.


Cellulitis is a common bacterial infection affecting the deep dermis and subcutaneous tissue characterized by signs of inflammation, such as redness, swelling, heat, and pain. Bacteria such as Streptococcus pyogenes and Staphylococcus aureus are common etiologic agents. Epidemiologic and systemic risk factors include the following:

  • Immunodeficiency
  • Having HIV, diabetes, kidney disease, liver disease, connective tissue disease, or malignancy
  • Having other dermatoses, fungal infections such as tinea pedis, venous disease, lymphedema
  • Iatrogenic causes like IV-line placement or surgical site interventions
  • Trauma wounds
  • Obesity
  • Pregnancy
  • Alcoholism

Cellulitis appears as ill-defined redness and swelling of the skin, and is usually warm to touch and painful. Cellulitis can affect all ages, but is more common in males than in females. The most common sites affected are the legs and digits. Other common sites include the face, hands, feet, trunk, neck, and buttocks. There can be blisters, erosions, ulcerations, or abscesses. Systemic symptoms include having fever, chills, and feeling sick or unwell.


Erysipelas is often mistaken for cellulitis as they share a lot of clinical features, however, instead of ill-defined borders, erysipelas presents with well-demarcated, clear, raised margins. Lesions present as red, edematous plaques that commonly affects the legs (in 76-90% of cases), face, and upper extremities.


Ecthyma initially begins as a small fluid-filled blister (vesicle) or pustule which eventually increases in size, forming a “punched-out” ulcer with yellowish-grayish crusts and purulent material. The margins can be violaceous and raised, with surrounding swelling or edema. Most common areas affected include the lower extremities, thighs, buttocks, and feet. Lymph nodes may or may not be swollen. Lesions of ecthyma often heal with scarring.


Erythrasma is a bacterial infection caused by the etiologic agent Corynebacterium minutissimum. This bacterium produces a red fluorescence that is visible when a Wood’s lamp is used to evaluate it. Lesions of erythrasma appear as well-defined reddish-brown patches with fine scales that usually occur on intertriginous areas (skin folds) such as web spaces of the feet, armpits, groin area, and inframammary areas. This is because intertriginous areas are usually warm and sweaty, providing an environment for C. minutissimum to proliferate, thus allowing erythrasma to develop.


Treatment varies depending on the type of bacterial infection. Most can be managed with topical and oral antibiotics, but it is best to consult with a physician to determine the best antibiotic of choice. Practicing good hygiene and proper handwashing can also help decrease the transmission of bacterial infections. Severe cases may need referrals to surgery or internal medicine, and is done on a case-by-case basis.

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About the Author:
Dr. Lauren Livelo is a board-certified dermatologist from the Philippines. She has a degree in Medicine from the University of the East Ramon Magsaysay Memorial Medical Center, and has completed her dermatology residency training in the Research Institute for Tropical Medicine. Aside from her private practice, she enjoys writing about skin care and diseases of the skin.


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