Calm offensive - tackling fungal infections

A conversation between a mother who has brought her young son into a pharmacy and the pharmacist, who sees them in the consultation area, goes like this:
“Can you help us with this?” the mother asks, opening up the boy’s shirt to reveal a disc shaped patch on his chest. It has an inflamed red border and is progressively paler towards the centre.
“How old is your son and how long has he had this?” asks the pharmacist.
“He’s six and it started a couple of weeks ago.”
“Does it itch?””
“Yes, he says it’s very itchy.”
“Have you seen your GP about this?”
“No. When I phoned for an appointment the receptionist said it didn’t sound urgent or serious and that I’d have to wait a fortnight for an appointment. She told me to put antispetic cream on it in the meantime. I have, but it hasn’t made much difference.”
“Do you have any pets at home?”
“No.”
“Has your son been anywhere special or different recently, that you can think of?”
The mother thinks for a moment. “Well, he went on a school trip to a petting farm about a week before the patch started appearing.”
“I think I know what it might be,” says the pharmacist. “I’ll give you something that should clear it up, but if there’s no improvement within a week or so you will have to take him to your doctor.”