Hi Welcome to Healthcare Magic.
The condition you have which is exactly the same which you have mentioned - Livedo
Reticularis which is characterized by mottled reticulated / Network like lines that appears as purplish discoloration of the skin due to diminished/obstruction in the blood supply of small blood vessels in skin. This condition is aggravated by cold exposure and most commonly appears on legs as re more prone for cold injury
, but can occur on upper limb or trunk.
Justin it most commonly a normal phenomenon in general population without any noticeable cause but can be intravascular obstruction or vessel wall disease.
As you are adolescent boy of 15 years, we take it granted that you do not have any other disease or health problem. So, you should not be worried about the problem. You can reduce it by preventing excessive exposure to cold.
Hope to have good cold season..
Dr Sanjay K Kanodia