Why did they become popular recently? Pain causes the release of endorphins, overall making you feel good. A similar concept as a runners high, except achievable watching TV on the couch.
Their original spread was likely for the same reason as most other spices, it could be used as a preservative by masking the taste of semi-rotten food.
Small amounts can cause a good amount of pain for those who aren't used to it. I remember putting crushed red pepper on a piece of pizza as a child and finding it unbearably hot.
Their original spread was likely for the same reason as most other spices, it could be used as a preservative by masking the taste of semi-rotten food.