Vascular lesions may appear as: Birthmarks are made of extra blood vessels in the skin. They are typically not inherited, but other relatives may have them as well. They are often subtle and noncancerous tumors of the cells that line blood vessels. They tend to have a pinkish-red discoloration and quickly grow. Birthmarks or growth composed of blood vessels can cause functional or cosmetic concerns. Small, raised red bumps with a smooth surface easily bleed because of the high number of blood vessels. They can develop after an injury.