Skin Infections

How skin infections happen

Intact skin is a strong barrier. Infection usually follows a break in that barrier, such as a cut, bite, burn, eczema, cracked heels or athlete's foot between the toes. Some germs (such as herpes viruses and scabies mites) spread by direct skin contact. Warmth, moisture and friction encourage fungi and yeast.

Bacterial skin infections

Most are caused by Staphylococcus aureus or group A Streptococcus.

If you are trying to decide whether a particular cut or patch is infected, see skin infection signs.

Viral skin infections

• Warts: rough growths caused by human papillomavirus (HPV). Common on hands and soles. Many go away within 2 years. Salicylic acid or freezing helps.
• Molluscum contagiosum: small, pearly bumps with a central dimple, common in children. Clears within 6 to 18 months.
• Cold sores (herpes simplex): tingling then clustered blisters on the lip. Antiviral medicine shortens outbreaks if started early.
• Shingles: a painful band of blisters on one side of the body from reactivated chickenpox virus. Antivirals within 72 hours help. A vaccine is recommended for adults 50 and older.
• Chickenpox, hand-foot-and-mouth disease and measles: body-wide rashes from viral infections.

Fungal skin infections

• Ringworm (tinea corporis): red, scaly, itchy ring with a clearer center. No worm is involved.
• Athlete's foot: itching, peeling and cracking between toes.
• Jock itch: red, itchy rash in the groin and inner thighs, usually sparing the scrotum.
• Scalp ringworm (tinea capitis): scaly patches and hair loss in children. Needs oral antifungals.
• Yeast (candida) infections: bright red, moist rash in skin folds with small satellite spots, common under breasts, in the groin and in diaper areas.
• Tinea versicolor: light or dark patches on the chest and back.
• Nail fungus: thick, discolored, crumbly nails.

Most skin fungal infections respond to over-the-counter terbinafine, clotrimazole or miconazole creams used for 1 to 4 weeks, and for a week after the rash clears.

Parasitic infestations

• Scabies: tiny mites burrow into the skin, causing intense itching worse at night and small bumps and lines between the fingers, on the wrists, waist and genitals. All close contacts must be treated at the same time with permethrin cream or oral ivermectin.
• Lice: head, body or pubic lice cause itching and visible nits.

Risk factors

• Diabetes, obesity and poor circulation
• Weakened immunity (chemotherapy, HIV, steroids, transplant medicines)
• Eczema and other skin conditions that break the barrier
• Swelling of the legs or lymphedema
• Crowded living, shared equipment, contact sports
• Hot, humid climates and occlusive footwear
• Older age and very young age

Diagnosis

Most skin infections are diagnosed by their appearance and history. Tests are used when the cause is unclear or treatment has not worked:

• Bacterial swab and culture of pus, especially to detect MRSA
• Skin scraping examined under a microscope with potassium hydroxide (KOH) for fungi or scabies mites
• Fungal culture of skin, hair or nail
• Viral swab (PCR) for herpes and shingles
• Wood's lamp (ultraviolet light) for some fungal and bacterial infections
• Blood tests and imaging for severe or deep infections

Treatment overview

• Bacterial: drainage of pus collections, topical antibiotics for limited impetigo, oral antibiotics for cellulitis and widespread infection, intravenous antibiotics in the hospital for severe cases.
• Viral: most are self-limiting. Antivirals (acyclovir, valacyclovir) for herpes and shingles. Wart treatments destroy infected tissue.
• Fungal: topical antifungals for most; oral antifungals for scalp, nail and extensive infections.
• Parasitic: permethrin, ivermectin, and washing bedding and clothes in hot water.

Do not use steroid creams on an unknown rash, as they can make fungal infections spread (tinea incognito).

Prevention

• Clean cuts promptly and keep them covered until healed.
• Keep skin moisturized to prevent cracks, and treat eczema and athlete's foot.
• Dry skin folds and between toes well. Wear breathable footwear and change socks daily.
• Do not share towels, razors, nail clippers or sports gear.
• Wear sandals in communal showers and pool areas.
• Keep vaccines up to date, including chickenpox, shingles and tetanus.
• Check feet daily if you have diabetes.

Frequently asked questions

What are the four types of skin infections?

Skin infections are grouped by cause: bacterial (cellulitis, impetigo, boils), viral (warts, cold sores, shingles, molluscum), fungal (ringworm, athlete's foot, yeast infections) and parasitic (scabies, lice). Each type is treated with a different kind of medicine.

How do I know if a skin infection is bacterial or fungal?

Bacterial infections are usually red, hot, swollen and painful, may ooze pus and can spread over hours to days. Fungal infections are typically itchy, scaly and spread slowly over weeks, often in rings or in warm, moist folds. A skin scraping can confirm a fungal cause.

What is the most common skin infection?

Fungal infections such as athlete's foot are among the most common skin infections overall. Among bacterial infections, cellulitis and infected boils are the most common reasons people see a doctor. In children, impetigo is very common.

Are skin infections contagious?

Many are. Impetigo, MRSA, ringworm, athlete's foot, warts, molluscum, cold sores, chickenpox, scabies and lice spread by skin contact or shared items. Cellulitis is not usually spread person to person. Handwashing and not sharing personal items reduce spread.

When does a skin infection need antibiotics?

Antibiotics are needed for spreading bacterial infections such as cellulitis, impetigo covering more than a small area, infected bites and wounds with spreading redness, and abscesses with surrounding cellulitis or fever. Small boils often need only drainage. Viral and fungal infections do not respond to antibiotics.