When the capillary walls widen and narrow too quickly they can cause the vessel walls to tear and the blood to leak out. Broken capillaries have a number of causes which include environmental and genetic factors, skin type, and even natural aging. The primary causes are aging and sun damage that cause the skin to become thinner and lose collagen. As collagen is a protein in the body that helps the skin stay firm and elastic, its loss makes the capillaries more vulnerable. Other reasons for broken capillaries include inflammatory conditions, excess pressure on the skin, extreme weather conditions and genetic predisposition. Broken capillaries are harmless and generally cause no pain or discomfort.