My son has a bruising behind one knee and in the crease of his forarm. Irregular in shape? We have eczema in my family.

Bruises. If you know that these bruises are caused by trauma like vigorous rubbing, then there should be no concern. If there has been no known injury and bruises (ecchymoses) appear elsewhere, a blood or clotting abnormality may be present and a physician should be consulted.