The spiciness of peppers is call pepper pungency. Pepper pungency is based on the Scoville Heat Scale whereas the mildest pepper, bell peppers, have 0 Scoville Heat Units (SHU) and the current Guinness Book of World Records record holder for the spiciest pepper is the Carolina Reaper has a max SHU of 2,200,000. We consider medium peppers as having less than 25,000 - 100,000 SHU. These peppers are quite spicy and may be too spicy for some people. As you consume hotter peppers your tolerance to capsaicin, the chemical that makes peppers spicy will build over time. In that case, what you once considered as very hot may now fall into this category. For someone who considers jalapeno peppers very spicy, medium heat pepper may be too spicy for them.