Diagnosis is made by identifying clinical features and ruling out conditions that mimic impetigo. Images of impetigo and its differential diagnoses can be found at www.dermnetnz.org.

• Non-bullous impetigo (also known as impetigo contagiosa or crusted impetigo) is the most common form.
• Lesions begin as vesicles or pustules, but these are rarely visible as they rapidly burst and evolve into gold-crusted plaques, typically 2 cm in diameter (these have been described as resembling glued-on cornflakes).
• The area around the mouth and nose is most commonly affected, although other areas of the face and the extremities may also be involved. Satellite lesions may occur due to autoinoculation.
• Non-bullous impetigo is usually asymptomatic, although there may be some itching. Systemic symptoms (such as fever) are uncommon unless the infection is widespread.
• Bullous impetigo commonly affects neonates, although older children and adults can also be affected.
• Bullous impetigo presents with flaccid, fluid-filled vesicles and blisters (bullae), that are usually at least 1–2 cm in diameter. These easily burst leaving raw skin, and eventually form thin, flat, brown-to-golden crusts.
• The face is less commonly affected than with non-bullous impetigo; instead bullous impetigo tends to involve the axillae, neck folds, and nappy area. Lesions are often multiple and spread rapidly.
• Unlike non-bullous impetigo, lesions tend to be painful. Systemic symptoms (weakness, fever, and diarrhoea) are more common, and there may be regional lymphadenopathy.
• Skin swabs are not necessary to diagnose impetigo. Take a swab (for bacterial identification and sensitivity) if the infection is:
• Very extensive or severe.
• Recurrent (consider nasal swab for staphylococcal carriage).
• Suspected as being a community outbreak.
• Suspected as being caused by meticillin-resistant Staphylococcus aureus (MRSA), for instance if the person has been in contact with a person who has been diagnosed with MRSA.