Hi Welcome to HCM. From your symptoms there seem to be a couple of reasons which could have caused your rash. As you mentioned the possibility of sunburn cannot be ruled out. It may burn or get dark and peel off later. Inspite of the sunblock it is possible. Also keep in mind that any other allergic reaction can be aggravated by sun exposure. So even without prior skin allergies, its possible that a batch of bad seafood can trigger a reaction. But itching would be more prominent. Its safe to say that its easily treatable. Apply a mometasone cream twice a day over the area for three days and taper it down to once daily for a few more days upto a week. If you experience burning or itching during the day, apply a soothing calamine lotion. Since you don t have any symptoms or itching you may not need antihistamines. In case you do, take a levocetrizine or fexofenadine tablet. Keep a check on spread of the rash or other symptoms. Hope this helps.