Boils (also called furuncles) and carbuncles are types of skin infections that develop when bacteria invade hair follicles or the surrounding skin, leading to painful, pus‑filled bumps.
Boils
A boil starts as a tender, red bump on the skin and typically progresses to form a central “head” filled with pus. Over a boil’s progression, it may grow in size, become warm and painful, then rupture and drain. Many boils go away on their own with home remedies, but larger boils may require medical attention.
Carbuncles
A carbuncle is a cluster of interconnected boils forming a deeper, more diffuse infection. Carbuncles tend to be more serious, often draining or “weeping” at multiple spots, and they are also more likely to cause systemic symptoms (fever, fatigue) and scarring if untreated.
Both boils and carbuncles tend to emerge in areas with hair follicles, where friction, sweat, or minor skin injuries are more common — for example, the face, neck, armpits, thighs, buttocks, or the back of the neck.
Boils can arise for a variety of reasons and are sometimes described differently based on the contributing factors. For example, you may hear people refer to heat boils (see below) when conditions like high temperatures, sweating, or heat stress contribute to their development–although in many cases the underlying cause is still a bacterial infection.
What Causes Boils?
Understanding what causes boils requires looking at how bacteria, skin integrity, and host factors interact with one another. Here are some of the key mechanisms that may often lead to boils on the skin:
Bacterial infection (most often Staphylococcus aureus)
The primary culprit of boils is Staph aureus, a bacterium commonly found on the skin or in the nose of healthy people. When it gains entry to deeper skin layers—through a hair follicle, minor cut, insect bite, or small abrasion—it can trigger an infection that leads to pus formation.
In recurrent or severe cases, lab cultures may be needed to identify antibiotic‑resistant strains, like MRSA (Methicillin-resistant Staphylococcus aureus).
Skin trauma, friction, and sweating
Minor skin breaks and trauma like scratches, insect bites, and shaving nicks can open a route for bacteria to infect the body. Friction and heat, especially in warm, moist environments, can also irritate skin and contribute to follicular stress, making it easier for bacteria to invade (hence the idea of “heat boils”). Wearing clothing that is too tight, chronic sweating, and poor hygiene may exacerbate the risk.
Host risk factors and comorbidities
Underlying conditions or behaviors may make some people more susceptible to boils and carbuncles than others. Here is a quick summary of some of these factors:
- Weakened immunity due to diabetes, HIV, chronic illness, or immunosuppressive therapies.
- Skin disorders such as eczema and acne that damage the skin barrier, making a bacterial infection easier.
- Close contact or sharing with someone who has a boil or carbuncle. Like many other contagious infections, Staph can spread via skin contact or shared personal items like towels or razors.
- Obesity, poor hygiene, or living conditions that increase sweating or reduce air flow to skin.
- Recurrent infection history. Some individuals experience repeated boils in the same area, possibly reflecting a local bacterial reservoir or host susceptibility.
Although the conditions leading to boils may vary, the outcomes are the same. Boils arise when bacteria gain access to a follicle or skin breach and multiply there, evoking a host inflammatory response that leads to pus formation.
Boils vs. Cysts: How to Tell the Difference
Because boils and cysts, as lumps under the skin, can sometimes look superficially similar, it’s useful to know how to distinguish them. Let’s consider how furuncles differ from cysts in each of the following characteristics:
Underlying Cause
- Boil: Bacterial infection of a hair follicle.
- Cyst: A closed sac or capsule filled with keratin, fluid, or other materials (noninfectious or sometimes secondarily infected).
Growth
- Boil: Onset is rapid; a boil may appear over days, become painful, and develop a pus-filled head, before eventually draining.
- Cyst: Growth is often slower; cysts may persist for weeks to months without sudden changes.
Pain Level
- Boil: Generally painful. Boils are tender, red, and warm, often swelling.
- Cyst: Usually less tender unless infected or inflamed.
Appearance
- Boil: Red bump with central “head” that may have surrounding redness.
- Cyst: Well-circumscribed, smooth, mobile lump. Many cysts have more of a white or flesh-colored appearance. Cysts are often not red unless inflamed or infected.
Drainage
- Boil: Tends to rupture and drain pus, with possible relief after drainage.
- Cyst: Without intervention, cysts often remain intact; can be aspirated or excised by a physician.
Recurrence Pattern
- Boil: May recur in similar locations, especially as the bacteria continues to colonize.
- Cyst: Cysts also can recur depending on origin (e.g. epidermoid cysts).
Treatment Focus
- Boil: Warm compresses (at home). A dermatologist can intervene with incision & drainage, or antibiotics when needed.
- Cyst: Surgical removal or excision (if bothersome), sometimes corticosteroid injection if inflamed.
In short, boils tend to behave in a way that is infectious and dynamic, while cysts tend to be static, noninfectious structures unless complications arise.
Of course, at-home examination cannot determine for sure what a skin lesion is. If you aren’t sure whether you are dealing with a boil or a cyst, it is best to get a medical professional to look at your skin lesion. In clinical practice, your dermatologist may evaluate the lesion, considering its history, palpation, imaging, and possibly drainage or biopsy, to decide whether it’s a boil, cyst, or another type of lesion entirely. A dermatologist may also be able to use lab cultures to test the infection for antibiotic sensitivity and MRSA, if that is a concern.
What Is a Stye?
A stye (or hordeolum) is, in essence, a boil-like infection of the oil glands (or eyelid follicles) at the base of an eyelash or within the eyelid. It is a localized, tender, red bump on the eyelid margin.
What to know about styes:
- Causes: Styes often stem from a bacterial infection—most commonly Staph species—of the eyelid’s sebaceous glands or eyelash follicles.
- Symptoms: Pain, swelling, tenderness localized to the eyelid; sometimes tearing, grit sensation in the eye, mild eyelid crusting.
- Treatment / self‑care:
- Use warm compresses to help soften and promote drainage. Hold a warm, damp washcloth on your eyelid for 10-15 minutes, several times per day.
- Gently cleanse your eyelid margin. Diluted baby shampoo solution is good for this.
- Avoid squeezing or poking the stye, or touching your eyes with anything that is not clean.
- Avoid eye makeup and contact lenses until healing is complete.
- When to see a doctor:
- If the stye persists beyond 7–10 days; this goes for most boils as well.
- If the stye becomes more painful, larger, or involves the entire eyelid.
- If there is vision impairment, spreading redness, or systemic symptoms (fever) accompanying the stye.
- In many cases, medical drainage and/or antibiotic therapy may be needed if the style does not respond to home remedies.
Because a stye is anatomically analogous to a boil, with the only difference being that it is restricted to the eyelid/oil gland region, it’s useful to view it in the same broader context of skin or follicular infections.
When Should I See a Dermatologist for Boils?
Most small boils heal with home care like warm compresses within a week or two. But in certain situations, it is recommended to consult a dermatologist or medical provider as the underlying bacterial infection can increase in severity and the boils may worsen.
Seek dermatologic evaluation if:
- The boil is on or near the face, nose, or around the eyes; these areas carry higher risk.
- The boil is characterized by marked pain that worsens rapidly, spreading redness, or signs of cellulitis (infection in the skin around the boil).
- The boil is accompanied by fever, chills, or feeling generally unwell; this may indicate systemic infection.
- Lesions are persistent, deep, or large and do not drain or heal within 7–14 days.
- Boils continue to recur in the same area or arise frequently across multiple sites; this may suggest deeper or chronic infection, staph carriage, or underlying conditions.
- You have an immunocompromised status or comorbidities (e.g. diabetes, cancer, HIV) where infection risks are greater.
- There is concern that the boil may be an antibiotic resistant strain (MRSA). Your dermatologist can order lab cultures to guide treatment as needed.
- Scarring or cosmetic concerns, as well as diagnostic uncertainty. A dermatologist can ensure proper excision, drainage, or biopsy if needed.
Possible medical treatment options:
There are several treatment options and steps a dermatologist may take to target the underlying infection causing your boils, depending on the severity and condition of the infection as well as your needs as a patient.
- Incision and drainage: When performed under sterile conditions, this is often an effective means to remove pus and relieve pressure.
- Antibiotic therapy: This treatment may either be systemic (targeting the whole body) or topical. Administration may vary, especially if there is surrounding cellulitis, systemic symptoms, or incomplete drainage. Your dermatologist will explain your options and recommend the best treatment method.
- Lab cultures: Your dermatologist may take a pus sample and analyze it to identify causative bacteria and antibiotic sensitivities.
- Follow‑up care: This is essential to monitor healing, prevent recurrence, and manage complications like scarring and spread.
At Vujevich Dermatology Associates, we offer comprehensive medical dermatology care. If you have persistent, recurrent, or complicated boils or carbuncles, our dermatologists can provide expert care including: evaluation and diagnosis, safe and sterile incision and drainage, or personalized antibiotic or adjunctive therapy as needed. We also are prepared to offer guidance on hygiene and staph decolonization, as well as advice to help you prevent future skin infections. We also encourage ongoing follow-up to monitor healing and address any scarring or complications as a result of the boils or carbuncles.
Your skin health is our priority, and we’re equipped to help manage boils, carbuncles, and other dermatologic conditions with medically sound, patient-centered care. Call us at 412-429-2570 or visit our contact page to book your appointment in the greater Pittsburgh, PA area. You can also follow us on Facebook and Instagram to see what’s new in the world of dermatology.