When certain part of my body heated up, red ring shaped rashes will pop out. are they ringworm? they will get bigger and itchy.

Hives: These sound like hives. There are many reasons to have hives including allergies however some people get them when they heat it up because a substance called histamine is released under the skin that causes these rashes. If it continues you should be seen by a doctor.

Explanation : Unlikely. Ringworms rash stable. Description of your rash look like vascular changes due to heat. Sunny dermatitis pretty itchy. Avoid long exposition to sun and heat. Use a lot of moisturizer. Be well.