Researchers from Pennsylvania State University have found that people who like spicy foods, don't necessarily have a high tolerance but rather have a specific type of personality. Researchers found that a love of chilli is associated with sensation seeking and reward. It was suggested that chilli lovers get desensitised to chilli burn over time, but there was no conclusive evidence.
100 volunteers were given liquid samples of capsaicin (the compound that gives chilli its burn) and asked to swirl in in their mouth of three seconds before spitting it out. They were then asked to rate the burning sensation and, in a separate questionnaire, rate their liking of various foods.
The article was very short and didn't follow through on how exactly the study got sensation and reward from the study. I was interested in this study initially because I love to eat spicy foods, and the study made sense. I haven't always liked spicy foods but now I love to try hotter and hotter foods. I would be interested in finding a follow up study that had more reliable results.