They seem to be made out of
dandruff or built up dead skin cells, but I use a specialized
shampoo that keeps my scalp moisturized since I've had dandruff issues before. The bumps leak a clear fluid when I scratch them off, and, as expected of an open "wound", sting when in contact with anything external. There is no specific odor that is identifiable, and I have not been able to see one of the bumps via a photo to determine color.