Hot sauces are measured these days in Scoville Units. The "Scoville Organoleptic Test" was developed in 1912 by Wilbur Scoville to measure the heat level of chili peppers. Pure ground chilies were mixed with sugar water, and a group of "testers" would taste the solution. The solution was diluted in equal increments until the “hotness” was no longer detected.
As an example, lets say you have a chile rated 3000 units. This means if you used 1 tablespoon of this chili, you would have to combine it with 3000 tablespoons of sugar water to dilute the concoction to where you no longer feel the heat!
Today, a lab test called High-Pressure Liquid Chromatography (HPLC) is used to determine the hotness of peppers and the capsaicin level or Scoville units of hot sauces. I guess it got too hot for human subjects to endure.
Many sauces reach ungodly heat ratings by extracting the oils from these various peppers that contain the capsasin instead of using the entire pepper. For these types of sauces, no more than a drop or two should be used on anything and are used more as an additive than a condiment. Anything with a heat rating over 500,000 should be used with caution. Make sure you read your sauce labels, most of them will tell you the Scoville Unit rating or at least how liberal you can be with the sauce.
Below is a table showing the heat rating for various peppers.