Ringworm
Ringworm is a fungal infection of the skin and/or nails. There are no worms, you'll be happy to know. It can be present anywhere on the skin, including the scalp, groin (jock itch), and toes (athlete's foot). It gets its name from the ringed rash it causes on the skin.
Ringworm is NOT a sign of bad hygiene, anyone can get it. The fungus can be transferred from person to person directly (e.g. wrestlers) or indirectly (from shared combs, clippers, shower floors, etc.). Pets can also be a source.
The rash is typically itchy and unsightly. It may start off looking like a pimple and progress to look like a pink coin on the skin. On the scalp it may show as a scaly, itchy rash with thinning of the hair in the involved area. Between the toes you may see redness and cracking. On the nails you may notice thickening and discoloration.
Ringworm on the skin usually responds to over-the-counter topical anti-fungal medications. However if it is the first time a child has such a rash, it may be a good idea to have it seen at the office as there are other rashes that can mimic ringworm. Ringworm on the scalp and nails usually require oral medications. Scalp ringworm may also benefit from certain shampoos (e.g. selenium sulfide) which your doctor or nurse practitioner can discuss with you.