We have had two boas with different skin problems.
The first had an all over dryness to his scales, inspite of correct humidity and soaking. His turned out to be a vitamin deficiency, which was corrected by injecting his rats with a vitamin supplement.
The second snake had several patches, about the size of a dime, that the scales were rough, appeared to be almost white, and were dry. He was like that for several months. We tried a couple different things on different patches and the treatment that cured it was clortrimazol cream, which is for athletes foot. After he shed you couldn't tell anything had been wrong. It is still a mystery how he got a fungus, if that is what it was.
I would still recommend you consult a vet, but if you are sure it isn't a burn, then it very well could be a fungus.
Kathy