Wrack

It begins with a roughening of the skin across the shoulders, rarely even noticed at first. The skin thickens, but does not change color, so visually there is little to see unless you are very close. There is no discomfort.
In typical cases, the process is gradual, but the area of the body affected continues to increase, with the skin of the upper arms and then the tops of the hands becoming affected. Oddly, the symptoms rarely move to the undersides of the arms or the palms of the hands. It acts almost like a cape, covering the upper portions of skin. 
Less common, but not unusual is the 'collar' effect, where the disease encircles the neck like a collar, even climbing to the base of the chin. It can happen as part of the more common symptoms, or be confined only to the neck in rare cases.

Causes

Medical technology in this time and place are not sufficient to pinpoint the cause, although there are many theories.

Treatment

Vigorous scrubbing of the affected areas seem to have limited effect, the skin thus removed is not replaced by normal skin. Oil, or creams, or ointments can soften, temporarily, the afflicted areas, but they do not provide a cure. Herbal treatments are likewise ineffective in the long view.

Prognosis

The Wrack is not life-threatening, but can impact the quality of life.  Some never recover. Others gradually find their condition improving and in some the disease disappears completely.  No pattern has yet been discovered that would identify the reasons behind the varied responses.

Epidemiology

Cause: Unknown
Carrier: Unknown
Cure: Unknown
The Wrack appears most often in the summertime.  It is most common near the sea and in river settlements.

Cultural Reception

Some find the condition to be very offensive and will avoid contact with any afflicted. Many in a society find it perfectly reasonable to jeer or bully those with symptoms. To some of the most ignorant, it is considered a curse and in a few instances has resulted in the victims being banished or killed.

Type

Bacterial

Rarity

Uncommon