This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Bier spots are a benign vascular anomaly characterized by white spots on the skin surrounded by a pale halo of erythema (redness). They are more common on the arms, the legs and the trunk. They are better observed when a tourniquet is placed around the affected arm or leg, and become less obvious when raising it. The spots are thought to be due to raised pressure constricting small veins (venous hypertension) and in most cases no cause is found (idiopathic). Bier spots usually affect healthy people, and may appear during pregnancy. But sometimes, they are part of a systemic disease such as cryoglobulinaemia, polycythaemia, scleroderma, aortic hypoplasia and coarctation, alopecia areata, Peutz-Jeghers syndrome, lichen planus, rapid heartbeat (tachycardia), lymphedema and excessive sweating of the hands (palmar hyperhidrosis). They are usually, self-limiting and except for counseling, require no treatment.
For more information, visit GARD.