Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Impetigo and Ecthyma


Wingfield E. Rehmus

, MD, MPH, University of British Columbia

Reviewed/Revised Jun 2023
Topic Resources

Impetigo is a superficial skin infection that leads to the formation of scabby, yellow-crusted sores and, sometimes, small blisters filled with yellow fluid. It is caused by Staphylococcus aureus, Streptococcus pyogenes, or both. Ecthyma is a form of impetigo that causes sores deeper in the skin.

Impetigo is common. It affects mostly children. Impetigo can occur anywhere on the body but most commonly occurs on the face, arms, and legs.

One form of impetigo causes blisters (bullous impetigo) that vary in size and can last for days to weeks.

Impetigo often affects normal skin but may develop after an injury or a condition that causes a break in the skin, such as a fungal infection, sunburn, or an insect bite. Poor hygiene and a moist environment are also risk factors. Some people have staphylococci or streptococci bacteria living in their nose that does not cause infection. They are called nasal carriers. Carriers are people who have the bacteria but do not have any symptoms caused by the bacteria. Carriers can move the bacteria from their nose to other body parts with their hands, sometimes leading to recurring infections or to spreading infection to other people.

Impetigo is very contagious—both to other areas of the person’s own skin and to other people.

Symptoms of Impetigo and Ecthyma

Impetigo and ecthyma are itchy and slightly painful. The itching often leads to extensive scratching, particularly in children, which serves to spread the infection.

Impetigo typically causes clusters of tiny blisters that rupture and develop a honey-colored crust over the sores (ulcers).

Bullous impetigo is similar except that the sores typically enlarge rapidly to form larger blisters. The blisters may appear as a red patch before forming larger blisters. They then burst and expose raw skin, which becomes covered with honey-colored crust.

Examples of Impetigo

Ecthyma is a form of impetigo. It is characterized by small, shallow ulcers that have a punched-out appearance and sometimes contain pus. The crust that covers the ulcers is thicker than the crust caused by impetigo. It is brown-black in color. The area around the ulcers is typically purplish red and swollen.

Diagnosis of Impetigo and Ecthyma

  • A doctor's evaluation

Doctors base the diagnosis of impetigo and ecthyma on the appearance of the sores and blisters.

In people who have repeated infections, a swab of the nose is taken and sent to the laboratory to determine whether they are a nasal carrier of staphylococci or streptococci.

Treatment of Impetigo and Ecthyma

  • Antibiotic ointments or creams

  • Sometimes antibiotic pills

The infected area should be washed gently with soap and water several times a day to remove any crusts.

Small areas of impetigo are treated with antibiotic ointments or creams applied directly to the skin (topically). If large areas are affected or are not cured with topical antibiotics, an antibiotic taken by mouth may be needed.

Ecthyma is usually treated with antibiotics taken by mouth.

People who are nasal carriers may be treated with topical antibiotics applied to the nasal passages.

quiz link

Test your knowledge

Take a Quiz!