Thanks for posting at HealthCareMagic. Your son seems to have developed allergic reaction to something he is exposed to in the swimming pool, a phenomenon commonly referred to as swimmer s itch. It is basically a contact dermatitis and staying away from the stimulus for sometime should help in relieving the situation. Some steroid ointment like hydrocortisone for a short duration along with antiallergic medication like levocetirizine should help. Hope that helps. Feel free to revert back in case of further queries if any.