Koreans use it when they feel hot or have a high body temperature and need to explain their condition.
Yes. "열이 나요 (yeori nayo)" is polite and natural. You can also say "열이 나 (yeori na)" casually.
You can say "I have a fever" — 열이 납니다 (yeori namnida).
열이 나요 means "I have a fever." Literally "fever comes out." 열 (yeol) = fever/heat, 이 (i) = subject marker, 나다 → 나요 (nada → nayo) = to come out → polite form. Common at hospital, pharmacy, or telling family/friends. Helps others understand your condition.
1. At hospital/pharmacy: Explain symptom.
2. Telling friends/family: Feeling sick.
3. Travel emergency: Need medicine.
I have a fever. Since yesterday.
I have a fever. I want to see a doctor. (Formal)
I have a fever. My body hurts so much. (Casual)
I have a slight fever. Do you have medicine?
• 열이 심해요 (yeori simhaeyo) - My fever is severe
• 열이 있어요 (yeori isseoyo) - I have a fever (alternative)
• 감기 걸렸어요 (gamgi geollyeosseoyo) - I caught a cold