Hi and welcome to HCM It seems to be an allergic rash. Did you just notice the rash or has it been there for a while? The possibilities are most commonly a bug or insect bite. Usually the action of rubbing off an insect when it bites, can cause a line like rash. Also note if you have any metallic or allergic object that has been in contact with your skin. Rule out causes like plants, outdoor activity, bed bugs, pets , any cosmetic application or procedure, food allergies,etc. An allergy should generally subside with an application of mild cortisone cream and antihistamine tablets. Note if any family members or contacts have similar complaints. If the rash spreads inspite of this, or you develop new symptoms, do consult a dermatologist to diagnose exactly and change the treatment as required. hope this helps you.