I do know that some of my friends have terrible allergies and have them coughing up small traces of blood. Usually their throat is very irratated because of allergies and the dry air.
if you think it's because of dry air and allergies, i suggest having a humidifier on and see if the helps. drink lots of fluids to keep your throat moist. if it becomes a sore throat do not drink extremely cold or extremely hot/warm liquids as it could irritate it some more.
if all else fails, see a doc
