Red tide, caused by toxic algal blooms, commonly affects coastal areas including Bataan, Cavite, Cebu, Guimaras, Iloilo, Masbate, Negros Occidental, Palawan, Pangasinan, Samar, Surigao del Norte, and Zambales. Exposure can cause nausea, vomiting, diarrhea, breathing difficulties, and skin irritation. Avoid affected waters and seek medical attention if exposed.