Hello i am 16 year-old male i have mark near chest

Patient: Hello . i am 16 year-old male . i have a weird mark between mu left side of my chest and my neck . it is not a birthmark because i got it at the age of 5 after going to the beach . what is it ?

Doctor: Hi.Thanks for your query.Note the history of weird mark between the left side of chest and my neck, got it at the age of 5 when you visited the beach.This must be a reaction to something in the sea or in sea-water, may be like some sea creature bite or touch that has got fixed into the skin as FDR.Consult a Dermatologist, tell Him the details and send me pictures.I hope this way the diagnosis will be definite.