My veins bust on the backs of my legs & the insides of my arms. it leaves enormous bruises. why does this happen? i'm healthy, 28 years old, not heavy

Capillary fragility: If you just had this in your legs, we would say you probably have venous hypertension and/ or venous insufficiency. This can be diagnosed at a vein center, with a venous doppler ultrasound exam: look up phlebologist in your area www.Phlebology.Org when you have in both, some people just have capillary fragility and there isn't much to do about this and not dangerous.

Low platelets: You need to be checked for bleeding tendency like low platelets including idiopathic thrombocytopenic purpura . Also friable blood vessels from vitamin c deficiency and vasculitis