Impetigo

Impetigo has one feature almost nothing else has: a thick, stuck-on, honey-coloured crust. If you can see that, impetigo is very likely.

What it looks and feels like

Where it shows up

• Around the nose and mouth — by far the most common place, especially in children.
• Hands, arms and legs — often starting on a scratch, a bite or a graze.
• The nappy area, armpits and neck folds — the usual sites for the blistering form in babies.
• Anywhere the skin was already broken — on top of eczema, a cold sore, a shaving cut or chickenpox spots. Impetigo landing on eczema is very common and is often mistaken for the eczema simply getting worse.

How it looks on different skin tones

On light skin the sores usually have a red rim. On brown and Black skin, that rim is more often brown, purple or grey, and it can be hard to see at all — but the golden crust looks the same on every skin tone, so that is the feature to go by. After it heals, the skin can be left lighter or darker for weeks to months. That is pigment change, not scarring, and it fades. Ordinary impetigo does not scar.

A few other things crust and weep. If yours does not fit the description above, see Lookalikes near the bottom of this page.

Impetigo is caused by bacteria, usually Staphylococcus aureus and sometimes Streptococcus pyogenes — the same strep that causes strep throat. Both live harmlessly on plenty of people's skin and in the nose. Impetigo happens when they get past the surface and start growing.

They need a way in, and that is usually something small: a scratch, an insect bite, a cold sore, a shaving nick, a runny nose that has rubbed the skin raw, or a patch of eczema. That is why it clusters in children, who have more scrapes and touch each other more, and why it is more common in warm, humid weather when skin stays damp. It spreads by direct contact with the sores or with anything that touched them — hands, towels, bedding, clothing, toys, sports equipment. Some people carry staph in their nose without knowing, which is one reason impetigo can keep coming back in the same person or the same household even after each round is treated properly. None of this reflects poor hygiene. It is an ordinary infection that spreads well among people who are in close contact.

Home care alone does not cure impetigo — it needs an antibiotic. What you do at home decides how fast it clears and whether it spreads to everyone else in the house.

Impetigo needs a prescription, so a visit — to a family doctor, a walk-in clinic or a dermatologist — is the normal path rather than the exception. Go sooner rather than later if:

• There are more than a few sores, or new ones keep appearing.
• The skin around the sores is getting red, warm, swollen or painful, or there is a fever. That suggests the infection is going deeper.
• The sores have not improved after three days of the prescribed treatment.
• It keeps coming back, in you or in someone else in the house.
• The sores are deep, punched-out and slow to heal rather than superficial and crusted.
• It is on a newborn, or on someone with a weakened immune system or poorly controlled diabetes.
• It has landed on top of eczema and the eczema is now much worse.

What the visit gets you: the right antibiotic for the bacteria that are actually there, a swab if the first treatment has not worked, and a plan for stopping it coming back if this is the third round in six months. A dermatologist is also the person to sort out the eczema underneath, which is usually the reason it keeps happening.

This is the part that does the work. A topical antibiotic is enough for a few sores in one area; pills are used when there are many sores, several body sites, or it is spreading despite the ointment.

Most impetigo clears without any lasting effect. The problems below are uncommon, and worth knowing so you can spot them early rather than worry about them.

Several things crust, weep or blister. The distinctions below matter, because two of them are made worse by the exact treatment impetigo needs, and one is an emergency.

• Cold sores (herpes) — a tight cluster of small blisters in the same spot every time, usually on the lip border, with tingling or burning a day before they appear. More painful than impetigo, and they crust over amber rather than honey-gold. Antibiotics do nothing for them.
• Eczema herpeticum — the cold sore virus spreading across eczema skin. Clusters of small, uniform, punched-out sores spreading fast, often with fever and real pain. This is the one that needs same-day care and antiviral treatment, and it is easy to mistake for impetigo on eczema.
• Infected eczema — eczema that has become weepy and yellow-crusted. It genuinely overlaps with impetigo and often needs both an antibiotic and eczema treatment. Very itchy, and there was a rash there before the crusting.
• Ringworm — a round patch with a raised scaly edge and a clearer middle. Scaly rather than crusted and weeping, and it needs antifungal treatment, not antibiotics.
• Contact dermatitis — an itchy, sometimes blistering rash shaped like whatever touched the skin. It can weep, but there is no honey crust and it settles when the trigger stops.
• Chickenpox — spots at different stages all over the body at once, with fever and a much itchier feel. Impetigo stays in one area unless it has been spread by fingers.
• Scabies — intense itch, worst at night, between the fingers and at the wrists, usually shared with someone else in the household. Scratched scabies can then get impetigo on top of it.
• Insect bites — itchy bumps in a scattered or clustered pattern. Scratched bites are one of the most common starting points for impetigo, so both can be present at once.