Greyscale

"Stone Men? Good luck stopping the spread of Greyscale with prayer. You'd have better luck dancing away the plague."

- Tyrion Lannister

Greyscale is a dreaded and usually fatal disease that can leave flesh stiff and dead, and the skin cracked and flaking, and stone-like to the touch. Those that manage to survive a bout with the illness will be immune from ever contracting it again, but the flesh damaged by the ravages of the disease will never heal, and they will be scarred for life.

Princess Shireen Baratheon caught greyscale as an infant and survived, but the ordeal left half of her face disfigured by the disease.

People afflicted by the disease are often called "Stone Men", due to how it makes their skin hard and dead. Stone Men are often pushed out from society, living in a colony established in ruins of Old Valyria.

Season 5
Gilly asks Shireen Baratheon what the disease is called that scarred half of her face, and Shireen explains that it is called "greyscale" and that she caught it as a baby but was cured before it could kill her. Gilly explains that she didn't know what its name was, but that two of her sisters had it and they both died. They were quarantined off from the other girls, but by the end their skin was completely covered in it, and they were no longer coherent but were acting like animals. At that point Craster dragged them out into the woods by a rope (so he wouldn't directly touch them), where he apparently mercy-killed and possibly burned them.

While in Volantis, Tyrion Lannister sees a Red Priestess of the Lord of Light giving a sermon to slaves in the street. She says that the Lord of Light hears the prayers of all men, king or slave, even the Stone Men in their misery. Tyrion quips to Varys that prayer isn't any more useful in curing greyscale than is trying to dance away the plague.

Stannis Baratheon explains to his daughter Shireen how she contracted greyscale as an infant, from an infected doll that he bought from a passing merchant ship from Dorne. By the time they burned the doll it was too late, and everyone said she would either die from the disease, or worse, live just long enough to become aware of the world before it was taken away from her. He was told that the best thing to do was to send her off across the Narrow Sea to live out her few years among the Stone Men in the ruins of Valyria. Stannis, however, refused to accept defeat, and instead brought every maester, healer, and apothecary he could find from both sides of the Narrow Sea to try everything they could to save her. Near-miraculously, the combination of their efforts actually managed to cure her, though the damage it had already done to her face was permanent..

As Jorah Mormont and Tyrion Lannister head to Meereen sailing through Valyria, they are ambushed by the stone men. Jorah manages to fight them off, but Tyrion is pulled underwater. When Tyrion wakes up, he finds himself on the shore, saved by Jorah. Unbeknownst to Tyrion, Jorah has been infected with the disease, having been touched on the wrist by one of the stone men.

Behind the scenes
According to Kerry Ingram (who plays Shireen), originally it took about three hours to apply the full Greyscale scarring makeup to the left side of her face, and about another two and a half hours to take it off. By Season 5, the makeup team managed to get the application time down to two hours.

In the books
In the A Song of Ice and Fire novels, greyscale generally affects children, especially in cold damp climates. The disease is encountered across both Westeros and Essos, even in the isolated lands Beyond the Wall. As it spreads, it leaves the flesh cracked and flaking, and hard to the touch like stone. The affected hardened areas of skin also turn mottled grey and black, though the TV series omitted this detail with Shireen.

Greyscale is considered a death sentence if contracted as an adult, though children have a slightly better chance of surviving it - though only in the sense that a handful of children have occasionally been cured of the disease. The symptoms can be stayed by limes, mustard poultices, and hot baths, though this is just delaying the inevitable. Greyscale kills very slowly, leaving its victims to suffer as their flesh deteriorates. Adults infected with greyscale can live a year or two, sometimes five, and it is not unknown for a few to live another ten years, but it always kills them in the end. In its very final stages, the disease turns inward, causing the flesh of muscles and organs to harden and die just like the skin in the outer tissue layers. It is also believed that cutting off any infected appendages can prevent it spreading throughout the body, though this treatment isn't always effective. Affected patches of flesh lose sensation: if someone is worried that they have caught the disease from an infected person, an early test before full symptoms appear is to prick the fingers and extremities with a knife on a daily basis. If that person can no longer feel the knife, it means they have greyscale.

Very rarely, children infected with greyscale can fight off the infection, though they are still left disfigured. It is feared that the disease still lies dormant in such children, though maesters insist that they are not infectious (i.e. Shireen's father Stannis, Davos, and the rest of their household do not fear that they can catch greyscale from her, but this is still a common superstition about people who survived greyscale). The wildlings still consider people who survive greyscale "unclean", and will euthanize any child that shows the symptoms. The wildlings call the disease the "grey death".

There is no one, confirmed cure for children affected with greyscale - it is just that healers who try a variety of methods sometimes end up succeeding. In the TV series, Stannis explains that he brought in every maester, healer, and apothecary on both sides of the Narrow Sea to try to cure Shireen, and the combination of their efforts ended up succeeding - which is apparently also what Stannis did in the novels. None of them know what they specifically did that cured Shireen, or if it was a combination of different methods: basically, in desperation they "threw everything in the shelf" at the disease, and somehow this managed to cure her.

A large area around the ruins of Chroyane, north of Volantis, in the Essos is even used as a large-scale colony for "Stone men", the name for those infected with greyscale. There are also vague rumors of men living in the shattered remains of the Valyrian Peninsula, in the ruins of Oros, Tyria, and Old Valyria itself - who might, similarly, be stone men pushed to live on the abandoned fringes of civilization - but these rumors are unconfirmed in the novels.

Greyscale has no direct real-life equivalent. It is somewhat similar to leprosy in that it tends to disfigure those infected with it, and in how society fears people with greyscale as "unclean". Unlike leprosy, some people occasionally manage to fight off greyscale, though their disfigurements never heal. In this respect, greyscale is loosely also similar to smallpox: people who contracted smallpox could recover from it, but they might be left with permanent and severe scarring.

While Shireen Baratheon was introduced in Season 3, no direct explanation was provided for the cause of her disfigurement in on-screen dialogue - meaning that it wasn't entirely confirmed that the disease was also called "Greyscale" in the TV continuity. It was only first mentioned by name in the updated HBO Viewer's Guide for Season 4, confirming the name. It was finally identified by name in Season 5 episode 2 "The House of Black and White" when Shireen and Gilly discuss it. Gilly said she didn't know what the disease was called north of the Wall, though that is probably due to her limited contact with other wildlings outside of Craster's Keep. There was no mention in the novels that two of her sisters died from greyscale, though this easily could have happened.