What it is
This common skin infection occurs when one of two types of bacteria (streptococci or staphylococci) enters baby's system through a break in the skin (e.g., a bug bite, a little scrape, a fingernail scratch, or a chickenpox blister). There are two forms of impetigo: bullous (with fluid-filled blisters that burst and leave a thin yellow-brown crust) and nonbullous (with thick yellow-crusted scabs and a lot of surrounding redness). Impetigo can cover thighs, buttocks, and lower abdomen and spread to other parts of the body as well.
What you can do about it
Impetigo thrives in the moist diaper area, so try to keep your baby's tush as clean and dry as possible (see Diaper Rash for tips on how). Keep baby's nails clean and clipped too, and when scrapes and cuts do happen, clean them with soapy water and a dab of Neosporin or Bacitracin. If your baby does get infected, you can help prevent the infection from spreading (and coming back) by gently washing the affected areas. Topical antibiotic ointments (like Bactroban) work well for mild cases, but oral antibiotics are faster and more reliable for severe or stubborn cases.
When to call the doctor
You might need a doctor to help confirm the diagnosis. Also, if the rash spreads or doesn't seem to be getting better, it's time to make the call.