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Boils and abscesses: causes, treatment, and warning signs

Clinical review pending

How boils differ from other skin abscesses, how to care for a small boil, when treatment is needed, and why these infections can return.

A hand holds an open blank book with three colored windows.

A painful, pus-filled lump on the skin may be a boil: an infection around a hair follicle that develops into a small abscess. Small boils can drain and heal on their own. Larger or deeper collections of pus often need a clinician to open them. Fever, spreading redness, or a lump that is not improving are reasons to have it examined. Squeezing it or cutting it open yourself can make the infection worse.

Boil or abscess: what is the difference?

A boil starts with an infection of a single hair follicle. Pus collects through the dermis, the deeper layer of skin, and into the fatty tissue beneath it, forming a small abscess. A skin abscess is the broader term for a contained collection of pus within the skin. It often feels like a tender, reddened lump with a center that gives slightly under pressure. A boil is therefore one type of abscess. Skin and soft tissue infection guideline

People often use the two words interchangeably. But several other skin problems can look similar, and the right treatment depends on what is actually causing the lump.

Boils

Bacteria can settle around a hair follicle and cause inflammation. When the infection extends deeper, a boil develops. In folliculitis, the inflammation stays nearer the surface, with pus limited to the epidermis. The starting point and the bacteria can be the same; the difference is how deeply the inflammation reaches. The medical word for a boil is a furuncle. Guideline

Skin abscesses

A skin abscess contains pus in the dermis and deeper skin tissues. A painful, tender, red lump with a yielding center is typical. Clinicians call this softness or movement fluctuance: it suggests there is liquid pus beneath the surface. Inflamed tissue without an abscess does not have this pus-filled cavity. Abscesses can also form elsewhere, including around a tooth, inside an organ, or in deeper soft tissue. Those conditions need their own assessment. Guideline

Carbuncles, cysts, and cellulitis

Superficial folliculitis can progress into a deeper boil. When several infected hair follicles join together, they form a carbuncle. The infection then involves the surrounding skin and deeper fatty tissue, and pus may drain through several openings. Carbuncles often occur on the back of the neck, back, and thighs, where the skin is thicker. Carbuncles

Cellulitis looks different. This infection spreads through the skin and tissue underneath it, producing an expanding area of redness rather than a distinct pocket of pus. It is unrelated to cosmetic cellulite. A cyst, meanwhile, is a tissue-lined sac that may remain uninfected and unnoticed for years. Once inflamed, it can resemble a boil. Keratin escaping through a ruptured cyst wall can itself trigger inflammation, even without a bacterial infection. Review of cellulitis

The size comparisons below are only illustrations. Size alone cannot reliably distinguish these conditions.

Skin problem Depth Typical size Cause Common locations Does it drain on its own? Usual treatment
Boil From a hair follicle into the fat beneath the skin Pea to grape Bacterial infection of one hair follicle Face, neck, armpits, buttocks, thighs Often, once a head develops Warmth and cleanliness; large boils may need incision and drainage
Skin abscess Dermis and deeper skin tissues Grape to golf ball or larger Bacteria contained within a pocket of pus Anywhere on the body, within skin or deeper tissues Sometimes, but not reliably Clinician-performed incision and drainage
Carbuncle Several connected hair follicles extending into deep tissue beneath the skin Larger than a single boil Two or more adjacent boils joining together Back of the neck, back, thighs Partly, through several pus-draining channels Clinician-performed incision and drainage
Epidermoid cyst A tissue-lined sac within the skin Pea to walnut Trapped keratin, initially without infection Face, neck, trunk, back Not normally, unless it ruptures or becomes infected Often left alone if symptom-free; acute inflammation may need drainage, with complete removal usually delayed until it settles
Cellulitis Deep dermis and tissue beneath the skin An expanding area rather than a lump Bacteria spreading through tissue Most often the legs, but possible anywhere No; there is no pocket of pus to drain Antibiotics rather than drainage

Sources and further reading: Guideline, carbuncles, cellulitis review, cellulitis guide, epidermoid cysts.

What causes boils and abscesses?

An infection often begins at a small break in the skin: a cut, an area irritated by shaving, or a patch rubbed raw by clothing. Bacteria enter, and the immune system tries to contain them within a pocket of pus. Staphylococcus aureus, usually shortened to S. aureus, is frequently involved. Reviews describe it as the most common cause of skin infections across age groups and regions worldwide. The severity of an infection also depends on the bacterium’s disease-causing characteristics, known as virulence factors. The number of bacteria alone does not explain how severe an infection will become. S. aureus review, S. aureus and skin infections

Containing the infection helps limit its spread, but it also makes treatment harder. A pus-filled cavity has a poor blood supply, limiting the access of immune cells and antibiotics. For carbuncles, abscesses, and large boils, the guideline therefore recommends opening the area and allowing pus to drain. This procedure is called incision and drainage. Guideline

Which bacteria are involved?

If an antibiotic is needed, the choice depends partly on the bacteria responsible. In a study of adults attending US emergency departments with pus-producing skin infections, S. aureus was identified in 76% of cases. Methicillin-resistant S. aureus, or MRSA, accounted for 59% of all cases. US emergency department study

Later randomized trials found MRSA in 45.3% of drained uncomplicated abscesses and 49.4% of smaller abscesses. These percentages describe the particular groups studied. They are not universal estimates for every skin abscess or every community. Uncomplicated abscess trial, smaller abscess trial

Who is more likely to develop them?

Boils are common, but their frequency varies across populations. A study in UK primary care recorded 512 first consultations for a boil or abscess per 100,000 person-years among women and 387 among men. People aged 16 to 34 were most likely to consult a clinician about one. A person-year combines the number of people observed with how long each was followed. UK cohort study

Observational studies have linked several characteristics with higher rates of infection or recurrence. A relative risk compares one group’s risk with another’s; it does not tell you how many people will develop the condition overall.

  • Obesity, diabetes, and smoking were each associated with a relative risk of 1.3 for recurrence. Study
  • For people younger than 30, the relative risk was 1.2. Study
  • After antibiotic use during the preceding six months, it was 1.4. Study
  • Adults with obesity had about 1.7 times the rate of skin infections requiring medical contact compared with adults of normal weight: the hazard ratio was 1.76 for women and 1.74 for men. Swedish cohort study
  • People with diabetes had higher infection rates in all 19 categories studied, including cellulitis. Diabetes and infection cohort study

These associations do not establish cause on their own. Nor can any one characteristic predict whether a particular person will develop a boil.

What do boils and abscesses look and feel like?

A boil begins as a warm, red lump that hurts when touched and grows over several days. As pus builds up, its center becomes softer and yields under pressure. A yellowish-white head often appears. Pressure and throbbing may be especially noticeable just before this happens. Guideline

Several openings or channels releasing pus suggest a carbuncle. In contrast, a broad area of redness that keeps expanding without a soft center suggests cellulitis. Redness, warmth, tenderness, and swelling increase as the infection spreads through tissue. Carbuncles, cellulitis

How a boil develops over several days

A boil can start as superficial folliculitis and occasionally develop into a carbuncle. The speed varies. The sequence below describes one possible course rather than a fixed timetable. How carbuncles develop

  1. A tender, red bump develops at a hair follicle irritated by shaving, friction, or another source of irritation.
  2. Over several days it grows larger and firmer, while the surrounding skin becomes red.
  3. Pus collects in the center and the tissue softens. A visible head sometimes forms.
  4. The boil drains on its own or is drained by a clinician.
  5. The cavity closes, tenderness eases, and the redness eventually fades.

If the lump keeps growing instead of settling, have it examined.

Are boils and abscesses contagious?

The bacteria involved can pass from one person to another, including within a household or through shared workout equipment and razors. Transmission does not necessarily lead to a boil. In a study of staphylococcal skin infections, S. aureus was detected in 40% of the people who originally had an infection and 50% of their household contacts. This is called colonization: bacteria are present, but they are not necessarily causing an active infection. Household colonization study

The bacteria can live in the throat and groin as well as the nose. In that study, swabbing only the nose would have missed 48% of the people who were colonized. Study

Surfaces can also carry bacteria. MRSA can survive on towels, razors, and furniture for hours to weeks and enter skin through cuts or scrapes. CDC: preventing MRSA

In one trial, people received either an antibiotic or placebo after an abscess was drained. Among participants who followed the treatment protocol and completed the required follow-up, new infections in household members were reported in 1.7% of the antibiotic group and 4.1% of the placebo group, measured 7 to 14 days after treatment ended. The finding is consistent with household spread, but it is not, by itself, a reason to take an antibiotic. Randomized trial

Caring for a small boil at home

Do not pick or squeeze a boil: doing so can spread the infection into nearby tissue. MRSA infections can also affect the bloodstream. That is a possible serious complication, not an inevitable consequence of squeezing a lump. CDC: MRSA basics, dermatologist guidance

For a small boil, warmth and cleanliness can help it come to a head and drain. Home care has limits, though. A large or deep boil, a boil on the face, or a lesion that is not improving needs medical assessment.

Warm compresses, step by step

The American Academy of Dermatology recommends the following timing for warm compresses. The cloth should feel comfortably warm, not hot enough to burn the skin.

  1. Wash your hands thoroughly before touching the area.
  2. Hold a clean, warm, damp cloth against the lump for about 10 to 15 minutes, three or four times a day. AAD: warm compresses
  3. Between compresses, cover the area with a clean, dry dressing. CDC
  4. If pus leaks out, change the dressing and wash your hands again immediately afterward.
  5. Wash the cloth and any towels or bedding that have touched the area. Do not share towels, washcloths, or razors. CDC: prevention

What to avoid

Do not squeeze, pierce, cut, or attempt to drain the boil yourself. Keep a draining lesion covered. Wash your hands before and after touching it, and clean any fabrics that have come into contact with the area.

Do not share towels, washcloths, or razors. Avoid shared baths and hot tubs while the skin is open.

When a boil or abscess needs medical treatment

For a carbuncle, an established abscess, or a large boil, drainage is the central treatment. Tablets cannot replace it. A clinician can assess whether the area needs to be opened and when. Guideline

This table is a guide, not a validated decision rule. Size and location alone do not determine treatment.

Situation When home care may be reasonable When to seek an examination
Size Small, roughly pea-sized, with a head developing Several centimeters across or continuing to grow; there is no fixed cutoff. An established abscess needs assessment for drainage
Location A small, improving boil on an arm, leg, or the trunk, without other warning signs A boil on the face needs early assessment. Near the spine or in the groin, deep pain, spreading inflammation, or an unclear cause also call for examination
Fever or feeling ill No symptoms affecting the whole body Any fever associated with the skin lesion
Duration Improving from day to day No improvement within 48 hours, or still present after two weeks
Recurrence within a year A single lesion Repeated episodes; 10% of affected people in one study had another boil or abscess within 12 months
Diabetes or weakened immunity Home care alone cannot be recommended as a blanket approach Seek medical assessment; substantially reduced immune defenses change how the infection is evaluated

Sources: Guideline, CDC: MRSA, recurrence study, NHS: boils and warning signs.

Incision and drainage

After numbing the area with a local anesthetic, the clinician opens the lesion and allows the pus to drain. A curette or surgical clamp can be used to release the internal partitions that divide the cavity into smaller pockets. A sample of pus is often sent to a laboratory to identify the bacteria. Carbuncles

The cavity was often routinely filled with dressing material afterward, a practice called packing. That routine is increasingly questioned. In a small randomized trial involving simple skin abscesses smaller than 5 cm, packing did not significantly reduce the need for another intervention at 48 hours, but it caused higher pain scores. Packing trial

The exact procedure depends on the treating clinician and the care setting. Draining an abscess is an established emergency medicine procedure that belongs in trained hands. Emergency department abscess care

When antibiotics are used

Whether to add an antibiotic after drainage depends on the expected benefit and potential harms. Important considerations include signs of an infection affecting the whole body, severely impaired immune defenses, multiple abscesses, very young or advanced age, and inadequate improvement after drainage alone. Guideline

In a trial of uncomplicated abscesses, cure after drainage occurred in 80.5% of those receiving trimethoprim-sulfamethoxazole and 73.6% receiving placebo. These were results from the modified intention-to-treat population, assessed 7 to 14 days after a seven-day treatment course. Randomized trial

Another trial studied abscesses no larger than 5 cm. At follow-up, 7 to 10 days after a 10-day treatment course ended, 83.1% of the clindamycin group and 81.7% of the trimethoprim-sulfamethoxazole group were cured, compared with 68.9% of the placebo group. Adverse events were more common with clindamycin. Smaller abscess trial

Most drained abscesses in these trials healed even without an antibiotic. Adding one improved the chance of cure to a limited extent and could reduce further infections or spread to others. Those benefits have to be weighed against possible side effects.

Warning signs: when to seek medical help

The following symptoms or circumstances call for a medical assessment of what to do next:

  • Fever, chills, or feeling generally unwell. Contact a healthcare professional. CDC
  • Redness spreading outward from the lump. This may indicate cellulitis, meaning the infection is no longer limited to a pocket of pus. Review
  • A boil on the face. A lesion near the spine or in the groin also needs examination if there is deep pain, spreading inflammation, or uncertainty about its cause. NHS
  • A larger lump or one that keeps growing, particularly if it is several centimeters across. This is not a rigid diagnostic cutoff.
  • No improvement within about 48 hours, or a lesion that is still present after two weeks.
  • Diabetes, medication that suppresses immunity, or another condition that substantially weakens immune defenses. Guideline
  • Severe pain that seems out of proportion to the size of the lesion.

Seek prompt advice for fever, spreading inflammation, a facial boil, or weakened immunity. Unusually severe pain or rapid deterioration needs immediate assessment. A slowly healing lesion without those warning signs still needs examination, but is not automatically an emergency.

How clinicians work out the cause

Boils and abscesses can usually be recognized by looking at and feeling the area. However, a physical examination does not always distinguish an abscess from cellulitis reliably. Ultrasound performed during the visit can help when the difference is unclear. Systematic review and meta-analysis

An analysis of 14 studies involving 2,656 patients evaluated this point-of-care ultrasound approach. Sensitivity was 94.6%, describing how well it identified an abscess when one was present. Specificity was 85.4%, describing how well it identified people who did not have an abscess. Ultrasound led to a change in management judged correct in 10.3% of cases and incorrect in 0.7%. For some patients, it helped avoid an unnecessary incision; for others, it identified a collection of pus where the skin had initially seemed simply inflamed. Meta-analysis

When a lesion is opened, a sample of pus is often sent to the laboratory. Growing bacteria from that sample, called a culture, helps identify the organism. It can show whether MRSA is involved and which antibiotic may be suitable if one is needed. Carbuncles

Why boils keep coming back

A boil or abscess can recur. In a UK study, 10% of people treated in primary care had another episode within 12 months. UK cohort study

US outpatient data found one-year recurrence rates of 16.4% to 19.0% for culture-confirmed staphylococcal skin infections. Among people without major underlying illnesses, a recurrence was usually followed by no further episode. About half of those second episodes occurred during the first three months. Retrospective database study

Persistent colonization with S. aureus is one possible contributor. Some people carry the bacteria on their skin and in their nose. Nasal carriage is associated with a higher risk of a later S. aureus infection. Nasal carriage review

For repeated infections, clinicians sometimes consider decolonization: treatment intended to remove the bacteria being carried. In a German village experiencing recurrent furunculosis, an outbreak ended after a rigorous program using antibiotic nasal ointment and antiseptic washes. Contact with an affected person was associated with more than six times the risk of furunculosis in that investigation: relative risk 6.8, with a 95% confidence interval of 3.2 to 14.3. This supports considering household contacts when infections keep returning. Outbreak investigation

Evidence for decolonization comes from particular patient groups and outbreak settings. It does not establish a benefit for everyone with a single boil. Whether it makes sense in an individual case should be discussed with a clinician; it is not a program to start on your own. Review

Which underlying conditions should be considered?

When boils recur, it can be worth investigating an underlying condition. One important distinction is hidradenitis suppurativa, also called acne inversa. Typical features include nodules, abscesses, tunnel-like tracts, and scars in the armpits, under the breasts, in the groin, or around the perineum. The pattern over time also matters: two or more recurrences within six months, or lesions persisting for at least three months, are described as part of the diagnostic assessment. Diagnosis and treatment review

A meta-analysis of 16 studies estimated a prevalence of 0.40% after adjusting for publication bias, with a 95% confidence interval of 0.26% to 0.63%. The studies came from Western Europe, Scandinavia, the US, and Australia, and estimates differed substantially by population and study method. The condition can remain unrecognized for years. Diagnosis review, prevalence meta-analysis

Blood glucose and body weight can also be relevant to an assessment. Diabetes and obesity are both associated with higher rates of skin infections. Diabetes and infection risk, obesity and infection risk

Metabolic problems do not always cause obvious symptoms. In US adults, estimates of undiagnosed diabetes as a proportion of all diabetes cases range from 9.5% to 17.8%. These numbers concern diabetes in the US population, not specifically people who have recurrent boils. Undiagnosed diabetes study

Reducing the risk of another boil

Hygiene measures help keep bacteria away from broken skin and reduce their spread:

  • Wash your hands regularly and shower or bathe after exercise.
  • Keep cuts and scrapes clean and covered until they close. CDC: preventing MRSA
  • Do not share towels, washcloths, razors, uniforms, or team clothing.
  • Place a towel or clothing between bare skin and shared equipment or surfaces.
  • Wash anything that comes into contact with a draining skin lesion.

These infections often develop where hair, clothing, or equipment rubs against the skin. The neck, thighs, armpits, and buttocks are common locations.

Weight, blood glucose, and smoking may also be relevant to a longer-term assessment. In the UK cohort, obesity, diabetes, and smoking were each associated with a relative risk of 1.3 for another boil. These are observed associations. They neither assign personal blame for an infection nor establish how much changing one of these factors would reduce the chance of recurrence. UK cohort study

How long do boils and abscesses take to heal?

According to the American Academy of Dermatology, most boils heal on their own within one to three weeks; warmth can help them drain. After a clinician drains an abscess, improvement usually begins within a few days, though the course can vary. These are not guaranteed healing deadlines. AAD: healing and care

In a trial of abscesses no larger than 5 cm, most participants had healed at follow-up, 7 to 10 days after a 10-day treatment course. This included 68.9% of those who received only placebo after drainage. The result cannot predict exactly how long an individual abscess will take to heal. Smaller abscess trial

Have the area examined if it has not begun improving within 48 hours of care, or if it remains after two weeks. CDC: MRSA, NHS: the two-week threshold

Frequently asked questions

What is the difference between a boil and an abscess?

A skin abscess is a contained pocket of pus in the skin. A boil is a particular type: it starts with an infected hair follicle, and the pus collection extends through the dermis into the fat underneath. Both can appear as tender, red lumps with a yielding center. Abscesses can be larger and deeper and can also develop outside the skin. Every boil is an abscess, but not every abscess starts at a hair follicle. Guideline

What causes boils and abscesses?

Bacteria enter through a break in the skin barrier, and the immune system tries to contain them within a pocket of pus. Staphylococcus aureus, described as the most common cause of skin infections worldwide, is frequently involved. In a study of adults attending US emergency departments with pus-producing skin infections, S. aureus was detected in 76% of cases, while MRSA accounted for 59% of all cases. Those percentages describe the group studied. S. aureus review, US emergency department study

Are boils contagious?

The bacteria responsible can spread, including within a household or through shared equipment. Not every transmission causes an infection. One study detected S. aureus in 40% of the people who originally had an infection and 50% of their household contacts. Carrying bacteria is not the same as being ill. MRSA can survive on towels, razors, and furniture for hours to weeks and enter the skin through cuts or scrapes. Household study, CDC: prevention

Should you pierce or squeeze a boil?

No. Picking or squeezing can spread bacteria into nearby tissue. Warm compresses may help a small boil drain on its own. Keep the area covered with a clean, dry dressing between applications. Larger or deeper lesions need medical care. The guideline recommends clinician-performed incision and drainage for carbuncles, abscesses, and large boils. CDC: MRSA, guideline

How long does a boil take to heal?

The American Academy of Dermatology says most boils heal on their own within one to three weeks; warmth can help them drain. A drained abscess usually begins improving within a few days. These are typical patterns, not fixed deadlines. AAD

In a trial involving abscesses no larger than 5 cm, 68.9% of participants given placebo after drainage were cured at follow-up. If there is no improvement within 48 hours or the lesion remains after two weeks, have it examined. Trial, CDC

Do boils and abscesses need antibiotics?

Most drained abscesses heal without antibiotics. Adding one can modestly improve the chance of cure: one trial of uncomplicated abscesses found cure rates of 80.5% with an antibiotic and 73.6% with placebo after drainage. A clinician weighs that benefit against potential harms. Relevant factors include signs that an infection is affecting the whole body, severely weakened immunity, multiple abscesses, very young or advanced age, and insufficient improvement after drainage alone. Trial, guideline

When should a boil be examined?

Fever or no improvement within 48 hours calls for medical assessment. A facial boil or an enlarging lump should also be examined. For a lesion near the spine or in the groin, deep pain, spreading inflammation, and an unclear cause matter, rather than location alone. An expanding area of redness without a soft center can suggest cellulitis. If you have diabetes or substantially weakened immunity, seek advice early. CDC, cellulitis review, guideline

Why do boils keep returning?

Carrying S. aureus is one possible contributor. People who carry it in their nose have a higher risk of a subsequent infection. In a UK primary care study, 10% of affected people had another boil or abscess within 12 months. US outpatient data found one-year recurrence rates of 16.4% to 19.0% for culture-confirmed staphylococcal skin infections. Recurrent lesions in the armpits or groin can also suggest hidradenitis suppurativa and are worth discussing with a clinician. UK cohort study, US database study, nasal carriage, hidradenitis suppurativa

Sources