Phossy jaw was a disfiguring ailment caused by poor working conditions in the 19th century. The condition was most frequently caused by exposure to white phosphorus, hence the name, although other chemicals have been known to cause similar conditions. Because this condition was such a visible and obviously painful disease, it became a rallying point for advocates for workers' rights and better regulation of working conditions, ultimately leading to increased labor regulation and the formation of government agencies to enforce these regulations.
More formally, phossy jaw is known as phosphorus necrosis of the jaw. It was caused by prolonged exposure to white phosphorus fumes, which were particularly associated with the match matching trade in the 19th century. At the time, other forms of phosphorus had been discovered and proved equally effective, but white phosphorus was cheap and readily available, so match companies continued using it despite the obvious health risks.
As the patient was exposed to the fumes, phosphorus accumulated in the jawbone and brain. The first signs of phossy jaw were often painful swellings along the side of the jaw, but it would quickly develop into a condition of open abscesses as the phosphorus essentially ate the jawbone away. A foul smelling discharge accompanied the condition, making victims unwelcome in social situations both because of the hideous malformation of their jaws and the stench. As the condition progressed, the patient's jaw would start to glow in the dark, due to a chemical reaction between the phosphorus and the air.
The only cure for phossy jaw was surgical removal of the jawbone. In an era of dicey anesthetics and before antibiotics, this procedure could potentially be very dangerous, in addition to being permanently disfiguring. Given that the match industry often employed very young children, the issue became a major source of public comment as labor activists published pamphlets about it and introduced people to young victims of phossy jaw.
The publicization of the problems with white phosphorus ultimately led to a ban on the substance in many nations, along with a general increase in labor regulations which was designed to address poor working conditions. Phossy jaw is now extremely rare, although unfortunately some developing nations appear to be experiencing an increase in industrial illnesses as they struggle to modernize their economies and manufacturing systems without corresponding regulations.