Schnauzer back or flea dirt?

Question
Hello Dr. Gotthelf,

I have a 7 year old Schnauzer.  About 3 days ago, I noticed on his back, above the tail, some crusty bumps that were beginning to mat up.  I combed out the mats gently, but some of the scabs did loosen from the skin, revealing kind of a wet skin underneath.  So I waited a couple of days, then last night I gave him a bath with Sebolux shampoo, and let it sit for about 8 minutes before I rinsed him.  Most of the crusty bumps did come off.  However, he did have a thumb-size lump that pussy blood came out of.  I figured one of the crusty bumps must have gotten infected.  To be safe, I took him to the vet today, and they were very busy, so the vet that he normally sees was busy and we had to see the new vet in with him.  I told her in detail what had transpired, and what I had done so far.  She said that the lump was probably an infected hair folicle and that he had "flea dirt".  She asked if he had been itching lately.  I said no, and I haven't seen any fleas on him.  He is treated with Frontline in the summer months but not now (we live in Illinois).  He is an inside dog, has regular groomings and I comb him out in between groomings.  Since Schnauzers' hair is so short, I think it would be easier to see fleas on them than other dogs.  But actually what I think she took as "flea dirt" was the remaining crusty skin from the "Schnauzer back syndrome" they are prone to.  I combed some of this material off his back and wet it, and it didn't turn red which would indicate dried flea fecal matter.  It actually floated, which would indicate skin cells.  Does it sound like she may have made a mistake?  She did prescribe an antibiotic for the infected lump, but also told me to give him a Frontline treatment.  When I got him home I looked him over throughly and I can't find any fleas.  What is your advice please?

Answer
If the "flea dirt" did not turn red, then it is probably oily secretions from the skin glands common to Schnauzers (comedones).  I like to use regular rubbing alcohol on these to dissolve some of the wax and oils and to dry the skin surface. If there is a cystic structure that is infected, the treatment from the vet will most likely help.