In short
Bacterial skin infections occur when harmful bacteria enter your body through breaks in the skin, and while many are mild and easily treated, some can become serious or even life-threatening if not properly managed.
What are bacterial skin infections?
Bacterial skin infections are illnesses or conditions caused by bacteria that invade your skin and the tissues beneath it. Your skin normally provides a remarkably good barrier against these infections. Although many bacteria come in contact with or live on your skin, they are normally unable to establish an infection. However, when bacteria enter the body through cuts, open wounds, or other breaks in the skin, they can cause infections that range from mild to serious.
When bacterial skin infections do occur, they can range in size from a tiny spot to affecting large areas of your body. They can also vary in seriousness, from harmless conditions to life-threatening situations.
What causes bacterial skin infections?
Many types of bacteria can infect the skin, but the most common ones are Staphylococcus (often called "staph") and Streptococcus (often called "strep"). These bacteria are responsible for most bacterial skin infections.
Certain bacteria commonly live on the skin of many people without causing any harm. However, these bacteria can cause skin infections if they enter the body through cuts, open wounds, or other breaks in the skin. Bacterial skin infections develop when bacteria enter through hair follicles (tiny pouches of skin that hold the roots of your hair) or through small breaks in the skin that result from scrapes, punctures, surgery, burns, sunburn, animal or insect bites, wounds, and pre-existing skin conditions.
About 25% to 30% of healthy people carry Staphylococcus aureus bacteria on their skin or in their nose without any infection occurring. This is called colonization. A special concern is Methicillin-resistant Staphylococcus aureus, also known as MRSA, which is resistant to many commonly used antibiotics. MRSA has become a common cause of bacterial skin infections in the United States.
Who is at higher risk?
Some people are at particular risk of developing bacterial skin infections. You are more likely to get an infection if you:
- Have diabetes, which can lead to poor blood flow, especially to the hands and feet, and a high level of sugar in your blood that decreases your ability to fight infection
- Are hospitalized or living in a nursing home
- Are older in age
- Have human immunodeficiency virus (HIV), AIDS, or other immune disorders, or hepatitis
- Are undergoing chemotherapy or treatment with other medications that suppress your immune system
Skin that is inflamed or damaged is more likely to become infected. In fact, any break in the skin makes a person more susceptible to infection. Children, people with poor hygiene, those who have close contact with infected individuals, and people with chronic skin conditions like eczema (a condition that makes skin dry, itchy, and inflamed) also have increased risk.
Common types of bacterial skin infections
Bacterial skin infections can be classified into different types based on how serious they are and which parts of the skin they affect.
Impetigo
Impetigo is a common bacterial skin infection caused by Group A Streptococcus (GAS) or Staphylococcus. It is most common in children and is very contagious. Symptoms usually begin 1 to 3 days after infection. Sores begin as small red spots, usually on the face, especially around the nose and mouth, but can appear anywhere on the body. The sores are often itchy but usually not painful.
The sores develop into blisters that break open and ooze fluid. This fluid contains infectious bacteria that can infect others if they have contact with it. After a few days, the ruptured blisters form a flat, thick, honey-colored (yellowish-brown) crust that eventually disappears, leaving red marks that heal without scarring.
Cellulitis
Cellulitis is a deep infection of the skin and the tissues beneath it. It is a painful, red infection of the skin that has poorly defined borders and is usually caused by Streptococcus or Staphylococcus bacteria. The infection commonly occurs near breaks in the skin, such as surgical wounds, trauma, or other skin problems, but it can also appear in skin that looks normal.
Common symptoms include redness or swelling of the skin, tenderness, warm skin, pain, and sometimes bruising, blisters, fever, headache, chills, or weakness. There may also be red streaks from the original site of the infection. Cellulitis commonly occurs on the legs and digits, followed by the face, feet, hands, torso, neck, and buttocks.
Folliculitis
Folliculitis is an inflammation of the hair follicles. When the infection is bacterial rather than mechanical in nature, it is most commonly caused by Staphylococcus. It looks like little pimples on a base of red, inflamed hair follicles. These bumps may ooze pus and can be itchy, painful, red, or swollen.
Furuncles and carbuncles
A furuncle, commonly called a boil, is a painful, firm, or fluid-filled bump that starts from an infected hair follicle. A carbuncle is a network of furuncles connected by channels under the skin. These deeper infections usually require incision and drainage by a doctor.
Erysipelas
Erysipelas is a skin infection most often caused by beta-hemolytic streptococci. This condition often affects the face or legs. Many people have a fever or flu-like symptoms. It appears as a shiny, red, raised rash with small blisters and enlarged and sore lymph nodes (small organs that help fight infection).
Other bacterial skin infections
Other types include erythrasma, a bacterial infection of the top layers of skin more common in the tropics, which mainly affects adults who are obese or have diabetes. Paronychia is an infection around a fingernail or toenail that can be caused by a break in the skin. Staphylococcal scalded skin syndrome is a serious infection that causes peeling skin over large parts of the body.
Signs and symptoms
While many bacterial skin infections are mild and easily treatable, some can become very serious and even life threatening. Symptoms may include redness, swelling, pain, or pus.
Most skin infections cause erythema (redness), edema (swelling), and other signs of inflammation. Buildup of pus in pockets (called furuncles) or fluid in blisters may form. Alternatively, infections may appear as scaling areas with no obvious inflammation.
Some symptoms that are common to many bacterial skin infections include rashes, swelling, redness, pain, pus, and itching. The specific symptoms depend on the type of infection you have.
How are these infections diagnosed?
To diagnose a bacterial skin infection, your healthcare provider will ask about your symptoms and perform a physical examination of the affected area.
In most cases, your healthcare provider will not conduct any tests. Clinical examination and staining or culturing of a sample of pus or discharge are often adequate for diagnosis. However, if you have a severe case, your healthcare provider may recommend tests to make sure the infection has not spread to other parts of your body.
These tests may include a blood test to confirm whether the infection has spread to your blood, a skin test to identify the type of bacteria responsible for your infection, or a bacterial culture using a sample from your skin. Your provider may take the sample by swabbing or scraping your skin or removing a small piece of skin (called a biopsy).
Treatment options
An antibiotic ointment is used if a minor skin infection develops. Antibiotics also need to be taken by mouth or given by injection if a large area of skin is infected.
If antibiotics are required, a medication that is active against gram-positive organisms such as penicillinase-resistant penicillins, cephalosporins (a class of antibiotics), macrolides (another class of antibiotics), or fluoroquinolones (a type of antibiotic for adults only) should be chosen.
Antibiotics should be maintained for at least three days after the resolution of acute inflammation. In more serious cases, you may need intravenous antibiotics delivered directly into a vein through a needle.
Abscesses (pockets of pus) should be cut open by a doctor and allowed to drain, and any dead tissue must be surgically removed.
Additional helpful treatments may include warm compresses, keeping the area clean, applying dressings as instructed, elevating the affected arm or leg if applicable, rest, and pain medicine as needed.
How to prevent bacterial skin infections
Preventing bacterial skin infections involves keeping the skin undamaged and clean. When the skin is cut or scraped, the injury should be washed with soap and water and covered with a sterile bandage.
Good hygiene practices are important. This includes washing your hands regularly with soap and warm water, cleaning and trimming your fingernails and toenails, regularly showering and thoroughly drying your skin after, wearing clean clothes, and keeping small wounds clean.
You should avoid sharing personal items such as towels, razors, cell phones, or athletic equipment that could spread bacteria. Group A Streptococcus (GAS) or "strep" can be transmitted through direct person-to-person contact with someone who has the infection, or picked up indirectly through contact with contaminated items.
If you have a bacterial skin infection, you should not practice or compete in sports until your medical provider clears you to return, especially for contagious infections like impetigo.
Doctors recommend that people do not use antibiotic ointments (prescription or nonprescription) on uninfected minor wounds because of the risk of developing an allergy to the antibiotic.
