Blood vessels that do not burst i have had one on the bottom of my foot for about 1 month. its very painful, but sometimes it reduces in size and reappears. is this a sign for a more serious problem

It : It sounds like you may be dealing with a varicose vein, although uncommon in the soles (bottom) of the feet, they can present in this area. There are some treatment options, including sclerotherapy (injecting the vein with a salt solution) or pain management with anti-inflammatory medications like advil or ibuprofen. Your primary care provider will refer you to a podiatrist and possibly a vascular surgeon for evaluation and treatment. Good luck.

Multiple reasons: Veins return blood back to the heart and can carry a large volume of blood. Depending on many factors including levels of hydration, genetics, outside temperature and even physical activity, the size of the veins will vary. Another important function of the veins is to help control body temperature and this too will affect vein size. Also with aging, veins enlarge as tissue volume decreases.