Bacterial Skin Infection

How bacterial skin infections develop

Healthy skin is a strong barrier. Bacteria such as staph live harmlessly on the skin or in the nose of about a third of people. Infection happens when they enter through:

• cuts, scrapes, burns, surgical wounds and insect bites
• cracks from eczema, dry skin or athlete's foot
• hair follicles irritated by shaving or friction
• injection sites

The depth of the infection determines the type and severity.

Types of bacterial skin infection

MRSA

MRSA (methicillin-resistant Staphylococcus aureus) is staph resistant to many common antibiotics. Community MRSA often causes painful abscesses, sometimes mistaken for spider bites. It spreads by skin contact and shared items, and is common in sports teams, prisons, military barracks and households.

Symptoms

• redness, warmth and swelling
• pain or tenderness
• pus, crusting or drainage
• fever, chills and feeling unwell in deeper infections
• swollen tender lymph nodes nearby
• red streaks spreading from the area (lymphangitis)

On darker skin, redness may look purple, brown or darker than the surrounding skin and can be harder to see. Warmth, swelling and pain are useful clues.

Risk factors

• breaks in the skin, eczema and athlete's foot
• diabetes
• obesity
• leg swelling or lymphedema, and previous cellulitis
• poor circulation
• weak immune system (chemotherapy, steroids, HIV)
• injection drug use
• crowded living conditions and contact sports
• poor hygiene or shared towels and razors

Diagnosis

Most bacterial skin infections are diagnosed by examination. A doctor may:

• swab pus from an abscess or wound to identify the bacteria and test antibiotic sensitivity, especially if MRSA is possible
• check blood sugar, especially in recurrent infections
• order blood tests and blood cultures in people who are very unwell
• use ultrasound to find a hidden abscess
• use CT or MRI, or urgent surgery, if necrotizing infection is suspected

Conditions that can mimic cellulitis include venous stasis dermatitis (usually both legs), contact dermatitis, gout and blood clots.

Treatment

Minor infections

• Clean the area with soap and water daily and keep it covered.
• Mild impetigo: antibiotic or antiseptic cream for a few days.
• Folliculitis: warm compresses, antibacterial wash; stop shaving the area for a while.
• Small boils: warm compresses several times a day to help them drain. Do not squeeze.

Abscesses

The main treatment is incision and drainage by a clinician. Antibiotics are added for larger abscesses, surrounding cellulitis, fever or high-risk patients.

Cellulitis and erysipelas

Oral antibiotics targeting strep (and staph where needed), usually for 5 to 10 days. Raise the affected limb and mark the edge of redness to track response. Improvement typically begins within 48 hours, though redness can take longer to fade. Severe cases need IV antibiotics in hospital.

Necrotizing infections

Emergency surgery to remove dead tissue, plus IV antibiotics and intensive care.

Pain relief

Acetaminophen (paracetamol) or ibuprofen, following the label dose.

Complications

• spread to deeper tissues, bone or joints
• sepsis
• recurrent cellulitis and lymphedema
• scarring
• post-streptococcal glomerulonephritis after strep impetigo (rare)

Prevention

• Clean and cover wounds promptly.
• Treat athlete's foot and keep skin moisturized if it cracks.
• Do not share towels, razors or sports gear; shower after contact sports.
• Control blood sugar in diabetes.
• Manage leg swelling with elevation and compression if advised.
• For recurrent staph infections, a doctor may recommend antiseptic body washes and a nasal antibiotic ointment for the whole household.

Frequently asked questions

What are the most common bacterial skin infections?

The most common are impetigo, folliculitis, boils and abscesses, cellulitis, erysipelas and infected wounds. Most are caused by staph or strep bacteria entering through broken skin. Mild infections are treated with wound care or creams; deeper ones need oral antibiotics or drainage.

How do I know if a skin infection is bacterial?

Bacterial skin infections are usually red, warm, swollen and tender, often with pus or honey-colored crusts, and may cause fever. Fungal infections tend to be itchy and scaly, and viral ones often cause blisters. A doctor can confirm the cause with an examination or swab.

Are bacterial skin infections contagious?

Some are. Impetigo and MRSA spread easily by skin contact and shared items such as towels and razors. Cellulitis itself is not usually contagious. Keep infected areas covered, wash hands often and avoid sharing personal items until healed.

When does a skin infection need antibiotics?

Antibiotics are needed for cellulitis, erysipelas, widespread impetigo, larger abscesses with surrounding redness, infections with fever, and infections in people with diabetes or weak immunity. Small boils and mild folliculitis often heal with warm compresses and hygiene.

What does MRSA look like on the skin?

MRSA often appears as a red, swollen, painful bump that may look like a pimple or spider bite and quickly fills with pus. It may be warm to the touch and come with fever. A swab of the pus confirms MRSA, and drainage is the main treatment.