An underlying blood disorder may be revealed by the appearance of red spots or blotches on the skin.

Medically termed purpura, the condition is common in older people, in whom it is usually a harmless consequence of the skin's aging, said Dr. Alec Goldenberg, a specialist in blood disorders at New York University Medical Center.In younger people, purpura is much rarer and is sometimes a warning sign of a blood disorder.

"Purpura is a catchall term for bleeding into the skin," Goldenberg said. "It generally appears as red spots or small patches."

Purpura is caused either by ruptures in the tiny blood vessels that lie underneath the skin, or, more seriously, by thrombocytopenia, an abnormal shortage of platelets, the blood cells essential to the clotting process.

"Thrombocytopenia can occur as a result of the body's forming antibodies to its own platelets," Goldenberg said.

Purpura can also be a symptom of certain infections, an allergic reaction to medications or leukemia.

The most common type of purpura, which affects older people, is generally harmless. "It is thought that as the skin ages, it becomes thinner and more brittle," Goldenberg explained. "Pressure can cause tiny blood vessels to rupture and leak blood into the skin."

The blotches, which may be as large as 5 centimeters (2 inches) across, may appear anywhere on the body but are generally on the legs or the backs of the hands.

More spots are likely to develop with age because the loss of protective skin tissue is irreversible and usually untreatable.

A medical history and physical examination can often rule out an underlying blood disorder. "A person's age, and where and how fast the purpura develops, are important clues to platelet problems," the physician said.

Blood tests for platelet counts and coagulation factors may be performed if a blood disorder is suspected.

"In older people, the rapid appearance of new purpura areas calls for evaluation," he added.

Symptoms of an underlying blood disorder include prolonged bleeding from cuts, nose bleeds, easy bruising, sores of the lip, mouth or throat and a general feeling of weakness.

Age-related purpura requires no treatment. Platelet-related purpura is treated by addressing the specific cause. If there is an immune problem, steroids may be prescribed as a countermeasure. If a drug reaction is suspected, the medication may be stopped or altered.