Rashes are common conditions with a variety of causes. Most rashes are not dangerous but rather a mere nuisance. Life-threatening skin rashes are rare, but when they do occur, you must seek immediate medical help.
Five potentially life-threatening disorders that have skin rash as the primary symptom are:
Acrocyanosis is blueness of the extremities (the hands and feet). Acrocyanosis is typically symmetrical. It is marked by a mottled blue or red discoloration of the skin on the fingers and wrists and the toes and ankles. Profuse sweating and coldness of the fingers and toes may also occur.
Acrocyanosis is caused by narrowing (constriction) of small arterioles (tiny arteries) toward the end of the arms and legs.
Rashes have blisters on top of them. Blisters that accompany a serious rash usually have the following features:
Blisters involve the thin outer layer of the skin that covers large parts of the body. This may mean several small blisters about 1 cm across or a few very large blisters several centimeters wide. Blisters are tense (full of fluid) at first, and then may become loose before breaking open. When they do rupture, the skin underneath is moist and usually painful. The underlying skin surface then dries up and crusts over.
Pressing on a tense blister or scratching the skin next to a blister will extend the blister and make it larger. This is a common feature of these skin disorders.
Blisters can involve any or all of the mucous membranes just listed. Blisters in these areas may not be noticeable because they rupture easily, especially in the mouth. Blisters on the mucous membranes that rupture may be very painful. When they occur in the mouth, pain makes it hard to eat or even drink.