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Pustule

What Is It, Causes, Diagnosis, Treatment, and More

Author:Maria Emfietzoglou, MD

Editors:Alyssa Haag,Emily Miao, PharmD,Kelsey LaFayette, DNP, RN

Illustrator:Jessica Reynolds, MS

Copyeditor:David G. Walker


What is a pustule?

A pustule refers to a pus-filled (i.e., circumscribed collection of white blood cells and serous fluid) cutaneous lesion that is up to one centimeter in diameter. Pustules are common in adolescents and are typically manifestations of underlying disorders, such as acne and folliculitis. They can appear isolated or in groups and may be localized in a single area or widespread throughout the body. While pustules can occur anywhere, they are more common on the face, chest, and back. 

Image of a hand with multiple clusters of pustules across the posterior aspect.

Is a pustule an infection?

A pustule is often indicative of an underlying infection; however, pustules may also be sterile and develop from various other non-infectious skin conditions, such as rosacea and psoriasis. In an infection, inflammatory cells, such as white blood cells, multiply and attempt  to fight the infection, ultimately resulting in the development of pustular lesions that contain dead microorganisms and inflammatory cells. 

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What causes pustules?

One of the most common causes of pustules are bacterial infections, typically due to Gram positive bacteria, such as Staphylococcus aureus or Streptococcus pyogenes. Examples of such infections include impetigo, which is a superficial, highly contagious infection typically affecting young children between the ages of two and five years old; folliculitis, which is a superficial infection of the hair follicles; furuncles, which are deeper infections of the hair follicles and surrounding tissue; and carbuncles, which are groups of two or more furuncles. Several viral infections can also lead to pustules, including chickenpox, a highly contagious infectious disease caused by Varicella Zoster virus, or VZV, and smallpox, a very contagious and potentially fatal disease caused by Variola virus. Fungal infections, such as dermatophyte infections (also known as tinea) as well as thrush (an oral infection due to Candida albicans) can also cause pustules. Additionally, pustules can develop in parasitic skin infections, such as scabies, which is an infestation of mites called Sarcoptes scabiei that cause intense itching. 

Pustules can also develop from non-infectious diseases. These include acne, a common skin condition in adolescents and young adults in which pores of the skin become blocked by ingrown hairs, oil, bacteria, or dead skin cells. Other non-infectious causes include drug eruption; rosacea, a chronic condition characterized by facial blushing or flushing in response to external stimuli, such as sun, heat, alcohol, spicy foods, and stress; and psoriasis, which is a chronic autoimmune disease typically characterized by well-circumscribed, erythematous patches covered with silvery scales.

What does a pustule look like?

Pustules are small lesions on the skin filled with pus. They are easily identified upon physical examination as red bumps with white or yellowish centers. If severe, they may be accompanied by additional signs and symptoms surrounding the lesion, such as pain, tenderness, swelling, soreness, and warmth. In some cases, fever as well as redness and pruritus around the lesion may also be seen.  

How are pustules diagnosed?

Diagnosis of pustules begins with careful physical examination and a thorough medical history. Certain aspects of the medical history can offer valuable information to guide the diagnosis, including the individual’s age, family history, list of medications, and presence of comorbidities. Physical examination typically involves assessing the size, shape, depth, location, distribution, and duration of the pustular lesions. Dermoscopy can be performed to examine skin lesions under a magnifying glass. If an infection is suspected, further diagnostic tests may be required to identify the causative microorganism, which may include microbial cultures for bacterial infections and a potassium hydroxide preparation for diagnosis of fungal infections. Finally, if pustules are medically reviewed but the diagnosis is still uncertain, a biopsy of the lesion can be performed.

How are pustules treated?

Management of pustules depends on the severity of the lesions and the underlying cause. In most cases, the lesions resolve on their own in a few days. There are various measures that may be recommended to reduce symptoms, speed up healing, and prevent further infection or scarring. These include regular washing with water and soap; avoiding irritants, like cosmetics; and avoidance of touching or popping the pustules. 

Individuals with pustules secondary to infection may benefit from antibiotics in the form of cream, lotion, gel or pills, or antifungal agents. Other treatment options include cortisone cream or dapsone gel. For acne, topical medications, such as benzoyl peroxide, salicylic acid, and retinoids, are commonly used. For rosacea, treatment also focuses on avoiding triggers and reducing the inflammation with topical metronidazole. Treatment for psoriasis depends on the severity and can include moisturizers and emollients; topical or systemic immunosuppressive therapies; ultraviolet (UV) phototherapy; and systemic medications, like antimetabolites, systemic retinoids, or biologic agents to help clear psoriatic plaques and minimize itchiness. 

What are the most important facts to know about pustules?

A pustule refers to a small, pus-filled cutaneous lesion that can develop anywhere on the body but is more common on the face, chest, and back. Pustules often result from infectious diseases due to bacteria, viruses, fungi, or parasites. However, they can also develop in other non-infectious skin conditions, such as acne, rosacea, and psoriasis. Diagnosis of pustules begins with physical examination and medical history, but further diagnostic tests, such as microbial cultures or biopsy, may be required. In most cases, pustules may not need to be treated at all; however, there are home remedies that can be used to speed up the healing. If pustules persist, individuals may benefit from medical advice and treatment with topical or oral agents.

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Related links

Skin lesions
Skin and soft tissue infections: Clinical practice

Resources for research and reference

Goldstein, B. G., & Goldstein, A. O. (2020). Approach to the patient with pustular skin lesions. In UpToDate. Retrieved February 25, 2022, from https://www.uptodate.com/contents/approach-to-the-patient-with-pustular-skin-lesions

Ogden, E. & Schofield, J. (2013). Benign Skin Lesions. Medicine, 41(7): 406–408. DOI: 10.1016/j.mpmed.2013.05.001

Valdez, M. A., Isamah, N., & Northway, R. M. (2015). Dermatologic Manifestations of Systemic Diseases. Primary Care: Clinics in Office Practice, 42(4): 607–630. DOI: 10.1016/S0095-4543(15)00107-4

Wolff, K., Goldsmith, L., Katz, S., Gilchrest, B., Paller, AS., & Leffell, D. (2011). Fitzpatrick's Dermatology in General Medicine (8th ed.). New York: McGraw-Hill.