Redcap is a neurological disorder that purely effects Fae, and is caused by out-of-control magic within the affected person's body damaging their brain and nervous system due to their magical potential far outstripping their ability to control it. As such, it is most common in Wild Mages and other denominations with high amounts of magical potential, and is also common within Fae who have become addicted to Spore due to its effect of exponentially increasing their magical ability.
The most common symptom, and the one that gives the disease its name, is an obsession with blood to the point of fetishisation. Sufferers will often bathe in the blood of animals or dead people, which over time will stain all the hair on their body the colour of congealed blood, hence the name. Reasons for this being a universal symptom of the disorder are currently being researched. Other symptoms include violent behaviour, psychosis, extreme paranoia, loss of rational thought, the rapid disintegration of the sufferer's personal moral compass and extreme impulsiveness.
Sadly, the disease is very difficult to cure, and is usually fatal as eventually the excess flow of magic will cause the nervous system to shut down completely, leading to encroaching paralysis and ultimately death.